Riitta Hari

YNIMG Journal 2020 Journal Article

Brain activity reflects the predictability of word sequences in listened continuous speech

• Miika Koskinen
• Mikko Kurimo
• Joachim Gross
• Aapo Hyvärinen
• Riitta Hari

Natural speech builds on contextual relations that can prompt predictions of upcoming utterances. To study the neural underpinnings of such predictive processing we asked 10 healthy adults to listen to a 1-h-long audiobook while their magnetoencephalographic (MEG) brain activity was recorded. We correlated the MEG signals with acoustic speech envelope, as well as with estimates of Bayesian word probability with and without the contextual word sequence (N-gram and Unigram, respectively), with a focus on time-lags. The MEG signals of auditory and sensorimotor cortices were strongly coupled to the speech envelope at the rates of syllables (4-8 ​Hz) and of prosody and intonation (0.5-2 ​Hz). The probability structure of word sequences, independently of the acoustical features, affected the ≤ 2-Hz signals extensively in auditory and rolandic regions, in precuneus, occipital cortices, and lateral and medial frontal regions. Fine-grained temporal progression patterns occurred across brain regions 100-1000 ​ms after word onsets. Although the acoustic effects were observed in both hemispheres, the contextual influences were statistically significantly lateralized to the left hemisphere. These results serve as a brain signature of the predictability of word sequences in listened continuous speech, confirming and extending previous results to demonstrate that deeply-learned knowledge and recent contextual information are employed dynamically and in a left-hemisphere-dominant manner in predicting the forthcoming words in natural speech.

YNIMG Journal 2018 Journal Article

Consistency and similarity of MEG- and fMRI-signal time courses during movie viewing

• Kaisu Lankinen
• Jukka Saari
• Yevhen Hlushchuk
• Pia Tikka
• Lauri Parkkonen
• Riitta Hari
• Miika Koskinen

Movie viewing allows human perception and cognition to be studied in complex, real-life-like situations in a brain-imaging laboratory. Previous studies with functional magnetic resonance imaging (fMRI) and with magneto- and electroencephalography (MEG and EEG) have demonstrated consistent temporal dynamics of brain activity across movie viewers. However, little is known about the similarities and differences of fMRI and MEG or EEG dynamics during such naturalistic situations. We thus compared MEG and fMRI responses to the same 15-min black-and-white movie in the same eight subjects who watched the movie twice during both MEG and fMRI recordings. We analyzed intra- and intersubject voxel-wise correlations within each imaging modality as well as the correlation of the MEG envelopes and fMRI signals. The fMRI signals showed voxel-wise within- and between-subjects correlations up to r = 0. 66 and r = 0. 37, respectively, whereas these correlations were clearly weaker for the envelopes of band-pass filtered (7 frequency bands below 100 Hz) MEG signals (within-subjects correlation r < 0. 14 and between-subjects r < 0. 05). Direct MEG–fMRI voxel-wise correlations were unreliable. Notably, applying a spatial-filtering approach to the MEG data uncovered consistent canonical variates that showed considerably stronger (up to r = 0. 25) between-subjects correlations than the univariate voxel-wise analysis. Furthermore, the envelopes of the time courses of these variates up to about 10 Hz showed association with fMRI signals in a general linear model. Similarities between envelopes of MEG canonical variates and fMRI voxel time-courses were seen mostly in occipital, but also in temporal and frontal brain regions, whereas intra- and intersubject correlations for MEG and fMRI separately were strongest only in the occipital areas. In contrast to the conventional univariate analysis, the spatial-filtering approach was able to uncover associations between the MEG envelopes and fMRI time courses, shedding light on the similarities of hemodynamic and electromagnetic brain activities during movie viewing.

YNIMG Journal 2016 Journal Article

Neural signatures of hand kinematics in leaders vs. followers: A dual-MEG study

• Guangyu Zhou
• Mathieu Bourguignon
• Lauri Parkkonen
• Riitta Hari

During joint actions, people typically adjust their own actions according to the ongoing actions of the partner, which implies that the interaction modulates the behavior of both participants. However, the neural substrates of such mutual adaptation are still poorly understood. Here, we set out to identify the kinematics-related brain activity of leaders and followers performing hand actions. Sixteen participants as 8 pairs performed continuous, repetitive right-hand opening and closing actions with ~3-s cycles in a leader–follower task. Subjects played each role for 5min. Magnetoencephalographic (MEG) brain signals were recorded simultaneously from both partners with a dual-MEG setup, and hand kinematics was monitored with accelerometers. Modulation index, a cross-frequency coupling measure, was computed between the hand acceleration and the MEG signals in the alpha (7–13Hz) and beta (13–25Hz) bands. Regardless of the participants' role, the strongest alpha and beta modulations occurred bilaterally in the sensorimotor cortices. In the occipital region, beta modulation was stronger in followers than leaders; these oscillations originated, according to beamformer source reconstructions, in early visual cortices. Despite differences in the modulation indices, alpha and beta power did not differ between the conditions. Our results indicate that the beta modulation in the early visual cortices depends on the subject's role as a follower or leader in a joint hand-action task. This finding could reflect the different strategies employed by leaders and followers in integrating kinematics-related visual information to control their own actions.

YNIMG Journal 2016 Journal Article

Social touch modulates endogenous μ-opioid system activity in humans

• Lauri Nummenmaa
• Lauri Tuominen
• Robin Dunbar
• Jussi Hirvonen
• Sandra Manninen
• Eveliina Arponen
• Anna Machin
• Riitta Hari

In non-human primates, opioid-receptor blockade increases social grooming, and the endogenous opioid system has therefore been hypothesized to support maintenance of long-term relationships in humans as well. Here we tested whether social touch modulates opioidergic activation in humans using in vivo positron emission tomography (PET). Eighteen male participants underwent two PET scans with [11C]carfentanil, a ligand specific to μ-opioid receptors (MOR). During the social touch scan, the participants lay in the scanner while their partners caressed their bodies in a non-sexual fashion. In the baseline scan, participants lay alone in the scanner. Social touch triggered pleasurable sensations and increased MOR availability in the thalamus, striatum, and frontal, cingulate, and insular cortices. Modulation of activity of the opioid system by social touching might provide a neurochemical mechanism reinforcing social bonds between humans.

YNIMG Journal 2015 Journal Article

Cortical kinematic processing of executed and observed goal-directed hand actions

• Brice Marty
• Mathieu Bourguignon
• Veikko Jousmäki
• Vincent Wens
• Marc Op de Beeck
• Patrick Van Bogaert
• Serge Goldman
• Riitta Hari

Motor information conveyed by viewing the kinematics of an agent's action helps to predict how the action will unfold. Still, how observed movement kinematics is processed in the brain remains to be clarified. Here, we used magnetoencephalography (MEG) to determine at which frequency and where in the brain, the neural activity is coupled with the kinematics of executed and observed motor actions. Whole-scalp MEG signals were recorded from 11 right-handed healthy adults while they were executing (Self) or observing (Other) similar goal-directed hand actions performed by an actor placed in front of them. Actions consisted of pinching with the right hand green foam-made pieces mixed in a heap with pieces of other colors placed on a table, and put them in a plastic pot on the right side of the heap. Subjects' and actor's forefinger movements were monitored with an accelerometer. The coherence between movement acceleration and MEG signals was computed at the sensor level. Then, cortical sources coherent with movement acceleration were identified with Dynamic Imaging of Coherent Sources. Statistically significant sensor-level coherence peaked at the movement frequency (F0) and its first harmonic (F1) in both movement conditions. Apart from visual cortices, statistically significant local maxima of coherence were observed in the right posterior superior temporal gyrus (F0), bilateral superior parietal lobule (F0 or F1) and primary sensorimotor cortex (F0 or F1) in both movement conditions. These results suggest that observing others' actions engages the viewer's brain in a similar kinematic-related manner as during own action execution. These findings bring new insights into how human brain activity covaries with essential features of observed movements of others.

YNIMG Journal 2015 Journal Article

Corticokinematic coherence mainly reflects movement-induced proprioceptive feedback

• Mathieu Bourguignon
• Harri Piitulainen
• Xavier De Tiège
• Veikko Jousmäki
• Riitta Hari

Corticokinematic coherence (CKC) reflects coupling between magnetoencephalographic (MEG) signals and hand kinematics, mainly occurring at hand movement frequency (F0) and its first harmonic (F1). Since CKC can be obtained for both active and passive movements, it has been suggested to mainly reflect proprioceptive feedback to the primary sensorimotor (SM1) cortex. However, the directionality of the brain–kinematics coupling has not been previously assessed and was thus quantified in the present study by means of renormalized partial directed coherence (rPDC). MEG data were obtained from 15 subjects who performed right index-finger movements and whose finger was, in another session, passively moved, with or without tactile input. Four additional subjects underwent the same task with slowly varying movement pace, spanning the 1–5Hz frequency range. The coupling between SM1 activity recorded with MEG and finger kinematics was assessed with coherence and rPDC. In all conditions, the afferent rPDC spectrum, which resembled the coherence spectrum, displayed higher values than the efferent rPDC spectrum. The afferent rPDC was 37% higher when tactile input was present, and it was at highest at F1 of the passive conditions; the efferent rPDC level did not differ between conditions. The apparent latency for the afferent input, estimated within the framework of the rPDC analysis, was 50–100ms. The higher directional coupling between hand kinematics and SM1 activity in afferent than efferent direction strongly supports the view that CKC mainly reflects movement-related somatosensory proprioceptive afferent input to the contralateral SM1 cortex.

YNIMG Journal 2015 Journal Article

MEG-compatible pneumatic stimulator to elicit passive finger and toe movements

• Harri Piitulainen
• Mathieu Bourguignon
• Riitta Hari
• Veikko Jousmäki

Magnetoencephalographic (MEG) signals recorded from the primary sensorimotor (SM1) cortex are coherent with kinematics of both active and passive finger movements. The coherence mainly reflects movement-related proprioceptive afference to the cortex. Here we describe a novel MEG-compatible stimulator to generate computer-controlled passive finger and toe movements that can be used as stimuli in functional brain-imaging experiments. The movements are produced by pneumatic artificial muscle (PAM), elastic actuator that shortens with increasing air pressure. To test the applicability of the stimulator to functional brain-imaging, 4-min trains of passive repetitive 5-mm flexion-extension movements of the right and left index finger and the right hallux were produced at 3Hz while the subject's brain activity was measured with whole-scalp MEG and finger or toe kinematics with an accelerometer. In all ten subjects studied, statistically significant coherence (up to 0. 78) occurred between the accelerometer and MEG signals at the movement frequency or its first harmonic. Sources of coherent activity were in the contralateral hand or foot SM1 cortices. Movement-evoked fields elicited with intermittent movements of the right index finger (once every 3. 2–4. 0s; mean±SD peak response latency 88±25ms) were co-located with the respective coherent sources. We further moved the right index finger at 3, 6, and 12Hz (movement ranges 5, 3, and 2mm, respectively), and analyzed the first 1, 2, and 4-min epochs of data. One minute of data was sufficient to locate the left hand area of the SM1 cortex at all movement frequencies. Sound-induced spurious coherence was reliably ruled out in a control experiment. Our novel movement stimulator thus provides a robust and reliable tool to track proprioceptive afference to the cortex and to locate the SM1 cortex.

YNIMG Journal 2015 Journal Article

Towards brain-activity-controlled information retrieval: Decoding image relevance from MEG signals

• Jukka-Pekka Kauppi
• Melih Kandemir
• Veli-Matti Saarinen
• Lotta Hirvenkari
• Lauri Parkkonen
• Arto Klami
• Riitta Hari
• Samuel Kaski

We hypothesize that brain activity can be used to control future information retrieval systems. To this end, we conducted a feasibility study on predicting the relevance of visual objects from brain activity. We analyze both magnetoencephalographic (MEG) and gaze signals from nine subjects who were viewing image collages, a subset of which was relevant to a predetermined task. We report three findings: i) the relevance of an image a subject looks at can be decoded from MEG signals with performance significantly better than chance, ii) fusion of gaze-based and MEG-based classifiers significantly improves the prediction performance compared to using either signal alone, and iii) non-linear classification of the MEG signals using Gaussian process classifiers outperforms linear classification. These findings break new ground for building brain-activity-based interactive image retrieval systems, as well as for systems utilizing feedback both from brain activity and eye movements.

YNIMG Journal 2014 Journal Article

Emotional speech synchronizes brains across listeners and engages large-scale dynamic brain networks

• Lauri Nummenmaa
• Heini Saarimäki
• Enrico Glerean
• Athanasios Gotsopoulos
• Iiro P. Jääskeläinen
• Riitta Hari
• Mikko Sams

Speech provides a powerful means for sharing emotions. Here we implement novel intersubject phase synchronization and whole-brain dynamic connectivity measures to show that networks of brain areas become synchronized across participants who are listening to emotional episodes in spoken narratives. Twenty participants' hemodynamic brain activity was measured with functional magnetic resonance imaging (fMRI) while they listened to 45-s narratives describing unpleasant, neutral, and pleasant events spoken in neutral voice. After scanning, participants listened to the narratives again and rated continuously their feelings of pleasantness–unpleasantness (valence) and of arousal–calmness. Instantaneous intersubject phase synchronization (ISPS) measures were computed to derive both multi-subject voxel-wise similarity measures of hemodynamic activity and inter-area functional dynamic connectivity (seed-based phase synchronization, SBPS). Valence and arousal time series were subsequently used to predict the ISPS and SBPS time series. High arousal was associated with increased ISPS in the auditory cortices and in Broca's area, and negative valence was associated with enhanced ISPS in the thalamus, anterior cingulate, lateral prefrontal, and orbitofrontal cortices. Negative valence affected functional connectivity of fronto-parietal, limbic (insula, cingulum) and fronto-opercular circuitries, and positive arousal affected the connectivity of the striatum, amygdala, thalamus, cerebellum, and dorsal frontal cortex. Positive valence and negative arousal had markedly smaller effects. We propose that high arousal synchronizes the listeners' sound-processing and speech-comprehension networks, whereas negative valence synchronizes circuitries supporting emotional and self-referential processing.

YNIMG Journal 2014 Journal Article

Spatial variability of functional brain networks in early-blind and sighted subjects

• Robert Boldt
• Mika Seppä
• Sanna Malinen
• Pia Tikka
• Riitta Hari
• Synnöve Carlson

To further the understanding how the human brain adapts to early-onset blindness, we searched in early-blind and normally-sighted subjects for functional brain networks showing the most and least spatial variabilities across subjects. We hypothesized that the functional networks compensating for early-onset blindness undergo cortical reorganization. To determine whether reorganization of functional networks affects spatial variability, we used functional magnetic resonance imaging to compare brain networks, derived by independent component analysis, of 7 early-blind and 7 sighted subjects while they rested or listened to an audio drama. In both conditions, the blind compared with sighted subjects showed more spatial variability in a bilateral parietal network (comprising the inferior parietal and angular gyri and precuneus) and in a bilateral auditory network (comprising the superior temporal gyri). In contrast, a vision-related left-hemisphere-lateralized occipital network (comprising the superior, middle and inferior occipital gyri, fusiform and lingual gyri, and the calcarine sulcus) was less variable in blind than sighted subjects. Another visual network and a tactile network were spatially more variable in the blind than sighted subjects in one condition. We contemplate whether our results on inter-subject spatial variability of brain networks are related to experience-dependent brain plasticity, and we suggest that auditory and parietal networks undergo a stronger experience-dependent reorganization in the early-blind than sighted subjects while the opposite is true for the vision-related occipital network.

YNIMG Journal 2014 Journal Article

Synchronous brain activity across individuals underlies shared psychological perspectives

• Juha M. Lahnakoski
• Enrico Glerean
• Iiro P. Jääskeläinen
• Jukka Hyönä
• Riitta Hari
• Mikko Sams
• Lauri Nummenmaa

For successful communication, we need to understand the external world consistently with others. This task requires sufficiently similar cognitive schemas or psychological perspectives that act as filters to guide the selection, interpretation and storage of sensory information, perceptual objects and events. Here we show that when individuals adopt a similar psychological perspective during natural viewing, their brain activity becomes synchronized in specific brain regions. We measured brain activity with functional magnetic resonance imaging (fMRI) from 33 healthy participants who viewed a 10-min movie twice, assuming once a ‘social’ (detective) and once a ‘non-social’ (interior decorator) perspective to the movie events. Pearson's correlation coefficient was used to derive multisubject voxelwise similarity measures (inter-subject correlations; ISCs) of functional MRI data. We used k-nearest-neighbor and support vector machine classifiers as well as a Mantel test on the ISC matrices to reveal brain areas wherein ISC predicted the participants' current perspective. ISC was stronger in several brain regions—most robustly in the parahippocampal gyrus, posterior parietal cortex and lateral occipital cortex—when the participants viewed the movie with similar rather than different perspectives. Synchronization was not explained by differences in visual sampling of the movies, as estimated by eye gaze. We propose that synchronous brain activity across individuals adopting similar psychological perspectives could be an important neural mechanism supporting shared understanding of the environment.

YNIMG Journal 2013 Journal Article

Coherence between magnetoencephalography and hand-action-related acceleration, force, pressure, and electromyogram

• Harri Piitulainen
• Mathieu Bourguignon
• Xavier De Tiège
• Riitta Hari
• Veikko Jousmäki

Hand velocity and acceleration are coherent with magnetoencephalographic (MEG) signals recorded from the contralateral primary sensorimotor (SM1) cortex. To learn more of this interaction, we compared the coupling of MEG signals with four hand-action-related peripheral signals: acceleration, pressure, force, and electromyogram (EMG). Fifteen subjects performed self-paced repetitive hand-action tasks for 3. 5min at a rate of about 3Hz. Either acceleration, pressure or force signal was acquired with MEG and EMG signals during (1) flexions–extensions of right-hand fingers, with thumb touching the other fingers (acceleration; free), (2) dynamic index–thumb pinches against an elastic rubber ball attached to a pressure sensor (pressure and acceleration; squeeze), and (3) brief fixed-finger-position index–thumb pinches against a rigid load cell (force; fixed-pinch). Significant coherence occurred between MEG and all the four peripheral measures at the fundamental frequency of the hand action (F0) and its first harmonic (F1). In all tasks, the cortical sources contributing to the cross-correlograms were located at the contralateral hand SM1 cortex, with average inter-source distance (mean±SEM) of 9. 5±0. 3mm. The coherence was stronger with respect to pressure (0. 40±0. 03 in squeeze) and force (0. 38±0. 04 in fixed-pinch) than acceleration (0. 24±0. 03 in free) and EMG (0. 25±0. 02 in free, and 0. 29±0. 04 in fixed-pinch). The results imply that the SM1 cortex is strongly coherent at F0 and F1 with hand-action-related pressure and force, in addition to the previously demonstrated EMG, velocity, and acceleration. All these measures, especially force and pressure, are potential tools for functional mapping of the SM1 cortex.

YNIMG Journal 2013 Journal Article

Decoding magnetoencephalographic rhythmic activity using spectrospatial information

• Jukka-Pekka Kauppi
• Lauri Parkkonen
• Riitta Hari
• Aapo Hyvärinen

We propose a new data-driven decoding method called Spectral Linear Discriminant Analysis (Spectral LDA) for the analysis of magnetoencephalography (MEG). The method allows investigation of changes in rhythmic neural activity as a result of different stimuli and tasks. The introduced classification model only assumes that each “brain state” can be characterized as a combination of neural sources, each of which shows rhythmic activity at one or several frequency bands. Furthermore, the model allows the oscillation frequencies to be different for each such state. We present decoding results from 9 subjects in a four-category classification problem defined by an experiment involving randomly alternating epochs of auditory, visual and tactile stimuli interspersed with rest periods. The performance of Spectral LDA was very competitive compared with four alternative classifiers based on different assumptions concerning the organization of rhythmic brain activity. In addition, the spectral and spatial patterns extracted automatically on the basis of trained classifiers showed that Spectral LDA offers a novel and interesting way of analyzing spectrospatial oscillatory neural activity across the brain. All the presented classification methods and visualization tools are freely available as a Matlab toolbox.

YNIMG Journal 2013 Journal Article

Primary motor cortex and cerebellum are coupled with the kinematics of observed hand movements

• Mathieu Bourguignon
• Xavier De Tiège
• Marc Op de Beeck
• Patrick Van Bogaert
• Serge Goldman
• Veikko Jousmäki
• Riitta Hari

To find out in which detail the kinematics of observed movements is represented in the viewer's brain, we searched for brain areas displaying coherent magnetoencephalographic (MEG) activity with observed repetitive hand movements. Whole-scalp MEG signals were recorded from 10 right-handed young adults who observed repetitive 3-Hz right-hand flexion–extension movements performed by the experimenter. The coherence between the subject's MEG signals and the experimenter's index-finger acceleration was computed to index the level of actor–observer coupling. The underlying cortical activity was identified with Dynamic Imaging of Coherent Sources. In all subjects, coherence spectra showed statistically significant peaks at movement frequency (F0) and its first harmonic (F1), strongest at visual areas. At F0, additional significant local coherence maxima, clearly distinct from the coherent visual areas, occurred in the primary motor (M1) cortices of both hemispheres and in the cerebellum (posterior vermis and hemispheres). Our results highlight the time-sensitive involvement of the M1 cortices and cerebellum in the kinematic representation of observed repetitive, non-goal directed motor actions.

YNIMG Journal 2012 Journal Article

Magnetoencephalography: From SQUIDs to neuroscience

• Riitta Hari
• Riitta Salmelin

Magnetoencephalography (MEG), with its direct view to the cortex through the magnetically transparent skull, has developed from its conception in physics laboratories to a powerful tool of basic and clinical neuroscience. MEG provides millisecond time resolution and allows real-time tracking of brain activation sequences during sensory processing, motor planning and action, cognition, language perception and production, social interaction, and various brain disorders. Current-day neuromagnetometers house hundreds of SQUIDs, superconducting quantum interference devices, to pick up signals generated by concerted action of cortical neurons. Complementary MEG measures of neuronal involvement include evoked responses, modulation of cortical rhythms, properties of the on-going neural activity, and interareal connectivity. Future MEG breakthroughs in understanding brain dynamics are expected through advanced signal analysis and combined use of MEG with hemodynamic imaging (fMRI). Methodological development progresses most efficiently when linked with insightful neuroscientific questions.

YNIMG Journal 2011 Journal Article

Functional motor-cortex mapping using corticokinematic coherence

• Mathieu Bourguignon
• Xavier De Tiège
• Marc Op de Beeck
• Benoît Pirotte
• Patrick Van Bogaert
• Serge Goldman
• Riitta Hari
• Veikko Jousmäki

We present a novel method, corticokinematic coherence (CKC), for functional mapping of the motor cortex by computing coherence between cortical magnetoencephalographic (MEG) signals and the kinematics of voluntary movements. Ten subjects performed self-paced flexion–extensions of the right-hand fingers at about 3Hz, with a three-axis accelerometer attached to the index finger. Cross-correlogram and coherence spectra were computed between 306 MEG channels and the accelerometer signals. In all subjects, accelerometer and coherence spectra showed peaks around 3–5Hz and 6–10Hz, corresponding to the movement frequencies. The coherence was statistically significant (P <0. 05) in all subjects, with sources at the hand area of the primary motor cortex contralateral to the movement. CKC appears to be a promising and robust method for reliable and convenient functional mapping of the human motor cortex.

YNIMG Journal 2010 Journal Article

Independent component analysis of short-time Fourier transforms for spontaneous EEG/MEG analysis

• Aapo Hyvärinen
• Pavan Ramkumar
• Lauri Parkkonen
• Riitta Hari

Analysis of spontaneous EEG/MEG needs unsupervised learning methods. While independent component analysis (ICA) has been successfully applied on spontaneous fMRI, it seems to be too sensitive to technical artifacts in EEG/MEG. We propose to apply ICA on short-time Fourier transforms of EEG/MEG signals, in order to find more “interesting” sources than with time-domain ICA, and to more meaningfully sort the obtained components. The method is especially useful for finding sources of rhythmic activity. Furthermore, we propose to use a complex mixing matrix to model sources which are spatially extended and have different phases in different EEG/MEG channels. Simulations with artificial data and experiments on resting-state MEG demonstrate the utility of the method.

YNIMG Journal 2009 Journal Article

Competing with peers: Mentalizing-related brain activity reflects what is at stake

• Marja-Liisa Halko
• Yevhen Hlushchuk
• Riitta Hari
• Martin Schürmann

Competition imposes constraints for humans who make decisions. Concomitantly, people do not only maximize their personal profit but they also try to punish unfair conspecifics. In bargaining games, subjects typically accept equal-share offers but reject unduly small offers; competition affects this balance. Here we used functional magnetic resonance imaging (fMRI) to study adjustment to competition in a bargaining game where subjects competed against another person for a share of the stake. For medium-sized, but not for minimum offers, competition increased the likelihood of acceptance and thus shifted behavior towards maximizing personal profits, emphasizing the importance of financial incentives. Specifically for medium-sized offers, competition was associated with increased brain activation bilaterally in the temporo-parietal junction, a region associated with mentalizing. In the right inferior frontal region, competition-related brain activation was strongest in subjects whose high acceptance rates in the standard ultimatum game hinted at a profit-oriented approach. The results suggest a network of brain areas supporting decision making under competition, with incentive-dependent mentalizing engaged when the competitor's behavior is difficult to predict and when the stake is attractive enough to justify the effort.

YNIMG Journal 2009 Journal Article

Dependencies between stimuli and spatially independent fMRI sources: Towards brain correlates of natural stimuli

• Jarkko Ylipaavalniemi
• Eerika Savia
• Sanna Malinen
• Riitta Hari
• Ricardo Vigário
• Samuel Kaski

Natural stimuli are increasingly used in functional magnetic resonance imaging (fMRI) studies to imitate real-life situations. Consequently, challenges are created for novel analysis methods, including new machine-learning tools. With natural stimuli it is no longer feasible to assume single features of the experimental design alone to account for the brain activity. Instead, relevant combinations of rich enough stimulus features could explain the more complex activation patterns. We propose a novel two-step approach, where independent component analysis is first used to identify spatially independent brain processes, which we refer to as functional patterns. As the second step, temporal dependencies between stimuli and functional patterns are detected using canonical correlation analysis. Our proposed method looks for combinations of stimulus features and the corresponding combinations of functional patterns. This two-step approach was used to analyze measurements from an fMRI study during multi-modal stimulation. The detected complex activation patterns were explained as resulting from interactions of multiple brain processes. Our approach seems promising for analysis of data from studies with natural stimuli.

YNIMG Journal 2007 Journal Article

Face recognition and cortical responses: Effect of stimulus duration

• Topi Tanskanen
• Risto Näsänen
• Helena Ojanpää
• Riitta Hari

To clarify the relationship between face perception and cortical activation, we manipulated the face recognition performance of 9 subjects by varying the duration (DUR) of stimuli while cortical neuromagnetic responses were recorded. A face image replaced a continuous pixel-noise mask for 17–200 ms, and the subject reported which of the pre-learned faces had been presented. Two cortical responses were clearly stronger to intact than phase-scrambled faces: the temporo-occipital response peaking at 140–200 ms (M170) and a more widely distributed response peaking at 200–500 ms (M300). For the shortest DURs (17–33 ms), face recognition was at chance level and the cortical responses negligible. For DURs of 50–83 ms, the proportion of recognized faces as well as the strength of cortical responses increased steeply. Recognition performance saturated at DURs of around 100 ms, whereas cortical responses continued to increase until the longest DUR of 200 ms. Amplitudes of both M170 and M300 were thus tightly correlated with recognition performance (r =0. 98), but comparison of the increment rates as a function of DUR showed the recognition performance to have an even closer similarity to M170 than to M300. In single-trial analysis the variability of response strengths increased in a direct proportion to response amplitude, demonstrating the averaged responses to be composed of graded rather than of all-or-nothing-type single responses.

YNIMG Journal 2007 Journal Article

Towards natural stimulation in fMRI—Issues of data analysis

• Sanna Malinen
• Yevhen Hlushchuk
• Riitta Hari

In search for suitable tools to study brain activation in natural environments, where the stimuli are multimodal, poorly predictable and irregularly varying, we collected functional magnetic resonance imaging data from 6 subjects during a continuous 8-min stimulus sequence that comprised auditory (speech or tone pips), visual (video clips dominated by faces, hands, or buildings), and tactile finger stimuli in blocks of 6–33 s. Results obtained by independent component analysis (ICA) and general-linear-model-based analysis (GLM) were compared. ICA separated in the superior temporal gyrus one independent component (IC) that reacted to all auditory stimuli and in the superior temporal sulcus another IC responding only to speech. Several distinct and rather symmetric vision-sensitive ICs were found in the posterior brain. An IC in the V5/MT region reacted to videos depicting faces or hands, whereas ICs in the V1/V2 region reacted to all video clips, including buildings. The corresponding GLM-derived activations in the auditory and early visual cortices comprised sub-areas of the ICA-revealed activations. ICA separated a prominent IC in the primary somatosensory cortex whereas the GLM-based analysis failed to show any touch-related activation. “Intrinsic” components, unrelated to the stimuli but spatially consistent across subjects, were discerned as well. The individual time courses were highly consistent in sensory projection cortices and more variable elsewhere. The ability to differentiate functionally meaningful composites of activated brain areas and to straightforwardly reveal their temporal dynamics renders ICA a sensitive tool to study brain responses to complex natural stimuli.

YNIMG Journal 2006 Journal Article

Quantification of mechanical vibration during diffusion tensor imaging at 3 T

• Jaana Hiltunen
• Riitta Hari
• Veikko Jousmäki
• Kiti Müller
• Raimo Sepponen
• Raimo Joensuu

Subjects sense clear mechanical vibrations during diffusion tensor imaging (DTI). These vibrations, likely resulting from diffusion-sensitizing gradients, have been assumed to be of the same strength and phase in all parts of the magnetic resonance imaging (MRI) scanner so that they could be ignored. However, our measurements, carried out from several parts of the MRI scanner and its surroundings using an optical laser-based interferometer, demonstrate an uneven distribution of mechanical vibrations within the scanner. The measurements were performed during DT scanning at 3 T, with various diffusion-weighting parameters, by positioning a phantom in the head coil and/or a human subject on the patient bed. The vibration-related movement was caused by the diffusion-sensitizing gradients and was maximally 0. 5 mm with typical settings used in brain imaging. The compensation for eddy currents, done with gradients in our DTI sequence, increased the vibration level by a factor of 1. 5 or more with diffusion-weighting parameter b = 1000 s/mm2 and by a factor of 3 or more with b = 3000 s/mm2. Mechanical vibrations stayed at an acceptable level with b ≤ 1000 s/mm2, resulting in additional signal losses of 5–17%. Vibration levels might be reduced by adjusting imaging parameters, by modifying the gradient waveforms in the DTI sequence, and by redesigning the mechanics of patient bed to effectively dampen the movements.

YNIMG Journal 2006 Journal Article

Touch activates human auditory cortex

• Martin Schürmann
• Gina Caetano
• Yevhen Hlushchuk
• Veikko Jousmäki
• Riitta Hari

Vibrotactile stimuli can facilitate hearing, both in hearing-impaired and in normally hearing people. Accordingly, the sounds of hands exploring a surface contribute to the explorer's haptic percepts. As a possible brain basis of such phenomena, functional brain imaging has identified activations specific to audiotactile interaction in secondary somatosensory cortex, auditory belt area, and posterior parietal cortex, depending on the quality and relative salience of the stimuli. We studied 13 subjects with non-invasive functional magnetic resonance imaging (fMRI) to search for auditory brain areas that would be activated by touch. Vibration bursts of 200 Hz were delivered to the subjects' fingers and palm and tactile pressure pulses to their fingertips. Noise bursts served to identify auditory cortex. Vibrotactile–auditory co-activation, addressed with minimal smoothing to obtain a conservative estimate, was found in an 85-mm3 region in the posterior auditory belt area. This co-activation could be related to facilitated hearing at the behavioral level, reflecting the analysis of sound-like temporal patterns in vibration. However, even tactile pulses (without any vibration) activated parts of the posterior auditory belt area, which therefore might subserve processing of audiotactile events that arise during dynamic contact between hands and environment.

YNIMG Journal 2005 Journal Article

Common cortical network for first and second pain

• Nina Forss
• Tuukka T. Raij
• Mika Seppä
• Riitta Hari

We measured, with whole-scalp magnetoencephalography, evoked fields from 10 healthy subjects to 1-ms thulium-laser stimuli that selectively activated nociceptive nerve fibers. The stimuli were delivered to the dorsum of the subject's left hand. The earliest cortical responses peaked at 165 ± 7 ms, agreeing with the conduction velocity of Aδ-fibers. To stimulate unmyelinated C-fibers, we modified the method of Bragard et al. [Bragard, D. , Chen, A. C. , Plaghki, L. , 1996. Direct isolation of ultra-late (C-fibre) evoked brain potentials by CO2 laser stimulation of tiny cutaneous surface areas in man. Neurosci. Lett. 209, 81–84], by decreasing the total energy of the laser beam and by restricting the size of the stimulated skin area to 0. 2–0. 3 mm2. The earliest cortical responses to these stimuli peaked at 811 ± 14 ms. Bilateral activation of the SII cortices was detected in all 10 subjects to Aδ and in 8 subjects to C stimuli, emphasizing the importance of the SII cortex in processing of pain. Additional activation was observed in the posterior parietal cortex (PPC), probably related to sensorimotor coordination targeted to produce precise motor acts that reduce or prevent the pain; the PPC activation may have been accentuated by the required continuous evaluation of the perceived pain. In contrast to some earlier studies, we did not observe activation of the primary somatosensory cortex (SI). Additional activations to both types of stimuli were detected in the cingulate cortex (three subjects) and in the bilateral insular cortex (two subjects). These results implicate that the nociceptive inputs mediated by the Aδ- and C-fibers are processed in a common cortical network in different time windows. Reliable temporospatial characterization of cortical responses to first and second pain offers a unique tool for basic and clinical neuroscience to study the two distinctive pain fiber systems at cortical level.

YNIMG Journal 2005 Journal Article

Oscillatory motor cortex–muscle coupling during painful laser and nonpainful tactile stimulation

• Andrej Stancak
• Tuukka T. Raij
• Marjatta Pohja
• Nina Forss
• Riitta Hari

Noxious stimulation activates–in addition to the brain structures related to sensory, emotional, and cognitive components of pain–also the brain's motor system. Effect of noxious input on the primary motor (MI) cortex remains, however, poorly understood. To characterize this effect in more detail, we quantified the ongoing oscillatory communication between the MI cortex and hand muscles during selectively noxious laser stimulation. The subjects maintained an isometric contraction of finger muscles while receiving the laser stimuli to the dorsum of the hand. Tactile stimuli with well-known effects on the MI cortex reactivity served as control stimuli. Cortex–muscle coherence was computed between magnetoencephalographic (MEG) signals from the contralateral MI and electromyographic (EMG) signals from the hand muscles. Statistically significant coherence at ∼20 Hz was found in 6 out of 7 subjects. The coherence increased phasically after both types of stimuli but significantly later after laser than tactile stimuli (mean ± SEM peak latencies 1. 05 ± 0. 12 s vs. 0. 58 ± 0. 06 s; P < 0. 05), and the coherence increase lasted longer after laser than tactile stimuli (0. 87 ± 0. 09 s vs. 0. 50 ± 0. 06 s, P < 0. 05). The observed coherence increase could be related to stabilization of the motor-cortex control after sensory input. Our findings add to the clinically interesting evidence about the cortical pain–motor system interaction.

YNIMG Journal 2005 Journal Article

Reproducibility of cortex–muscle coherence

• Marjatta Pohja
• Stephan Salenius
• Riitta Hari

Cortex–muscle coherence is a frequency-analysis technique that has been increasingly applied in the investigation of movement disorders. To study the intra- and inter-session stability of the cortex–muscle coherence, we recorded from 12 healthy subjects magnetoencephalographic (MEG) and surface electromyographic (EMG) signals during unilateral isometric contractions of the left- and right-hand muscles. Two identical measurements were performed during one session, and the session was repeated once after about 1 year. In one experienced subject, the recordings were repeated seven times within 20 months. The MEG–EMG coherence exceeded the noise level in 10 out of 12 subjects. Both the frequency (correlation coefficient r = 0. 77–0. 93, P < 0. 01) and strength (r = 0. 78–0. 91, P < 0. 01) of coherence were well reproducible within each session for both left- and right-sided contractions. The inter-session reproducibility was high for the mean of cumulative coherence frequency (r = 0. 90–0. 95, P < 0. 01), but relatively low for coherence strength (r = 0. 43–0. 59, P > 0. 05). The results for one subject participating in 8 repeated sessions strongly supported the results of the whole group. Thus, intra-session reproducibility of both strength and frequency of the cortex–muscle coherence is good and studies comparing different conditions at the group level within one session are feasible. However, caution is needed when interpreting absolute levels or changes in the strength of coherence in single subjects between the sessions.

YNIMG Journal 2005 Journal Article

Viewing speech modulates activity in the left SI mouth cortex

• Riikka Möttönen
• Juha Järveläinen
• Mikko Sams
• Riitta Hari

The ability to internally simulate other persons' actions is important for social interaction. In monkeys, neurons in the premotor cortex are activated both when the monkey performs mouth or hand actions and when it views or listens to actions made by others. Neuronal circuits with similar “mirror-neuron” properties probably exist in the human Broca's area and primary motor cortex. Viewing other person's hand actions also modulates activity in the primary somatosensory cortex SI, suggesting that the SI cortex is related to the human mirror-neuron system. To study the selectivity of the SI activation during action viewing, we stimulated the lower lip (with tactile pulses) and the median nerves (with electric pulses) in eight subjects to activate their SI mouth and hand cortices while the subjects either rested, listened to other person's speech, viewed her articulatory gestures, or executed mouth movements. The 55-ms SI responses to lip stimuli were enhanced by 16% (P < 0. 01) in the left hemisphere during speech viewing whereas listening to speech did not modulate these responses. The 35-ms responses to median-nerve stimulation remained stable during speech viewing and listening. Own mouth movements suppressed responses to lip stimuli bilaterally by 74% (P < 0. 001), without any effect on responses to median-nerve stimuli. Our findings show that viewing another person's articulatory gestures activates the left SI cortex in a somatotopic manner. The results provide further evidence for the view that SI is involved in “mirroring” of other persons' actions.

YNIMG Journal 2005 Journal Article

Yearning to yawn: the neural basis of contagious yawning

• Martin Schürmann
• Maike D. Hesse
• Klaas E. Stephan
• Miiamaaria Saarela
• Karl Zilles
• Riitta Hari
• Gereon R. Fink

Yawning is contagious: Watching another person yawn may trigger us to do the same. Here we studied brain activation with functional magnetic resonance imaging (fMRI) while subjects watched videotaped yawns. Significant increases in the blood oxygen level dependent (BOLD) signal, specific to yawn viewing as contrasted to viewing non-nameable mouth movements, were observed in the right posterior superior temporal sulcus (STS) and bilaterally in the anterior STS, in agreement with the high affinity of STS to social cues. However, no additional yawn-specific activation was observed in Broca's area, the core region of the human mirror-neuron system (MNS) that matches action observation and execution. Thus, activation associated with viewing another person yawn seems to circumvent the essential parts of the MNS, in line with the nature of contagious yawns as automatically released behavioural acts—rather than truly imitated motor patterns that would require detailed action understanding. The subjects' self-reported tendency to yawn covaried negatively with activation of the left periamygdalar region, suggesting a connection between yawn contagiousness and amygdalar activation.

YNIMG Journal 2004 Journal Article

Activation of the human primary motor cortex during observation of tool use

• Juha Järveläinen
• Martin Schürmann
• Riitta Hari

Tool use is a characteristic human trait, requiring motor skills that are largely learned by imitation. A neural system that supports imitation and action understanding by directly matching observed actions and their motor counterparts has been found in the human premotor and motor cortices. To test whether this “mirror-neuron system” (MNS) would be activated by observation of tool use, we recorded neuromagnetic oscillatory activity from the primary motor cortex of 10 healthy subjects while they observed the experimenter to use chopsticks in a goal-directed and non-goal-directed manner. The left and right median nerves were stimulated alternatingly, and the poststimulus rebounds of the ∼20-Hz motor-cortex rhythms were quantified. Compared with the rest condition, the level of the ∼20-Hz rhythm was suppressed during observation of both types of tool use, indicating activation of the primary motor cortex. The suppression was on average 15–17% stronger during observation of goal-directed than non-goal-directed tool use, and this difference correlated positively with the frequency of subjects' chopstick use during the last year. These results support the view that the motor-cortex activation is related to the observer's ability to understand and imitate motor acts.

YNIMG Journal 2004 Journal Article

Cortical activation during a spatiotemporal tactile comparison task

• Jussi Numminen
• Martin Schürmann
• Jaana Hiltunen
• Raimo Joensuu
• Veikko Jousmäki
• Seppo K Koskinen
• Riitta Salmelin
• Riitta Hari

Tactile sensory memory is needed to infer shape or motion from the spatiotemporal pattern of sensory input during manual exploration. Here we applied triplets of pressure pulses to the fingertips of subjects who were asked to respond when successive triplets were the same (COMPARE task) or when a particular stimulus was included in a triplet (CONTROL task). Stimulus sequences (30 s) alternated with rest blocks (30 s) and functional magnetic resonance images (fMRIs) were acquired in a 1. 5-T scanner. During the COMPARE task, we found enhanced activation in inferior parietal cortex, supplementary motor area (SMA), and right dorsolateral prefrontal cortex (DLPFC). Activation of DLPFC is likely to be related to the attempt to memorize the stimulus sequences and activations of SMA and inferior parietal cortex to the analysis of temporospatial tactile patterns and, more generally, to guidance of haptic exploration. In addition, task-specific activation was seen in anterior cingulate gyrus, possibly related to the high mental effort required by the comparison task. Our rhythmic tactile stimulus as such, without any task-specific enhancement, activated also left cerebellum and (mainly left) putamen, supporting the idea that these structures are related to perception of temporal order of tactile stimuli.

YNIMG Journal 2004 Journal Article

Distal-to-proximal representation of volar index finger in human area 3b

• Yevhen Hlushchuk
• Nina Forss
• Riitta Hari

In area 3b of the monkey primary somatosensory cortex SI, the proximal phalanges of the fingers are represented close to the surface and the fingertips in the depth of the central sulcus. To study whether a similar arrangement might exist in humans, we applied tactile stimuli to the distal and proximal phalanges of the index finger in 11 healthy adults. Cortical somatosensory evoked fields were recorded with a whole-scalp neuromagnetometer. The sources of the responses were situated in the posterior wall of the central sulcus, statistically significantly more superior to proximal than distal stimuli, with a mean difference of 3. 1 mm. Thus the distal-to-proximal representation of the index finger shows a similar order in human and monkey SI cortex.

YNIMG Journal 2004 Journal Article

Modulation of motor-cortex oscillatory activity by painful Aδ- and C-fiber stimuli

• Tuukka T. Raij
• Nina Forss
• Andrej Stancák
• Riitta Hari

Spontaneous ∼20-Hz oscillations, arising predominantly from the primary motor cortex (MI), are readily observed by magnetoencephalography (MEG). Prior studies have indicated that the level of the ∼20-Hz rhythm reflects the functional state of the MI cortex: increased 20-Hz level is associated with increased inhibition and suppression of the rhythm with excitation of MI. Close interaction is suggested between pain and the motor system by the association of chronic pain with motor dysfunction and by the alleviation of pain by motor-cortex stimulation. We therefore explored the effect of noxious input on motor-cortex functions by recording MEG signals from nine healthy subjects during selective laser stimulation of Aδ- and C-fibers of the hand. The ∼20-Hz level was suppressed in the contralateral MI cortex in all nine subjects after painful Aδ- and C-fiber stimuli (P < 0. 001). The suppression started 180 ± 10 ms (mean ± SEM) after Aδ-fiber stimuli and 820 ± 30 ms after C-fiber stimuli, and peaked 160–170 ms later. Similar, but about 50% weaker, suppression of the ∼20-Hz oscillations occurred in seven out of nine subjects in the ipsilateral MI. These results suggest automatic, lateralized, excitation of the MI cortex by noxious Aδ- and C-fiber input.

YNIMG Journal 2003 Journal Article

Comparison of BOLD fMRI and MEG characteristics to vibrotactile stimulation

• Pasi I Tuunanen
• Martin Kavec
• Veikko Jousmäki
• Jussi-Pekka Usenius
• Riitta Hari
• Riitta Salmelin
• Risto A Kauppinen

The characteristics of blood oxygenation level-dependent (BOLD) fMRI and magnetoencephalographic (MEG) responses to vibrotactile stimuli in humans were studied and compared. The stimuli, presented with interstimulus intervals (ISIs) ranging from 1 to 5 s, yielded highly reproducible MEG responses, with current dipoles in the primary somatosensory (SI) cortex in all subjects. BOLD fMRI responses to similar stimuli showed substantial intrasubject variation in the activation sites around the SI cortex. BOLD responses were detected in all subjects in the secondary somatosensory (SII) cortices as well, with comparable BOLD response amplitudes to those in the SI cortex. Current dipoles, used to model the MEG signals, were stronger at longer ISIs than shorter ISIs. The BOLD response amplitudes did not show a similar dependence on ISI, but the activated brain area was larger when longer ISIs or longer stimuli were applied. Our results support the view that combined use of brain mapping methods provides complementary information and should be considered in functional brain examinations.

YNIMG Journal 2002 Journal Article

Comparison of Minimum Current Estimate and Dipole Modeling in the Analysis of Simulated Activity in the Human Visual Cortices

• Linda Stenbacka
• Simo Vanni
• Kimmo Uutela
• Riitta Hari

Magnetoencephalographic(MEG) data are typically interpreted using source models because of the nonunique inverse problem. Although single current dipoles, adequately representing local active areas, can be identified accurately, multiple and overlapping sources form a challenge for MEG modeling. We tested the performances of multidipole modeling and minimum current estimate (MCE) in the analysis of complicated source configurations. Simulated current sources were placed to physiologically meaningful areas of the human visual cortices. Ten volunteers from the laboratory staff analyzed four different simulations with both dipole modeling and MCE without prior information of the sources. In general, the same sources were found using both modeling methods. The subjects tended to report more false sources with MCE than with dipole model, in part due to their inexperience with the method. Dipole model was more accurate than MCE both in time and space for nonsimultaneous sources but both methods performed similarly when sources overlapped in time. For all source configurations, considerably smaller source amplitudes were reported with MCE than with dipole model.

YNIMG Journal 2002 Journal Article

Left-Hemisphere-Dominant SII Activation after Bilateral Median Nerve Stimulation

• Cristina Simões
• Flamine Alary
• Nina Forss
• Riitta Hari

We used bilateral median nerve stimuli to find out possible hemispheric dominance in the activation of the second somatosensory cortex, SII. Somatosensory evoked fields (SEFs) were recorded from 14 healthy adults (7 right-handed, 7 left-handed) with a 306-channel neuromagnetometer. Electrical stimuli were applied once every 3 s simultaneously either to the left and right median nerves at the wrists or to the palmar skin of both thumbs. Sources of SEFs were modeled with four current dipoles, located in the SI and SII cortices of both hemispheres. The SI activation strengths did not differ between the hemispheres, whereas the SII responses were significantly stronger in the left than in the right hemisphere. In right-handers, the left/right SII ratios were 1. 9 and 1. 8 for wrist and thumb stimuli, respectively. The corresponding values were 1. 5 and 1. 7 in left-handers. The results indicate handedness-independent functional specialization of the human SII cortices.

YNIMG Journal 2002 Journal Article

Mind's Ear in a Musician: Where and When in the Brain

• Martin Schürmann
• Tommi Raij
• Nobuya Fujiki
• Riitta Hari

The temporospatial pattern of brain activity during auditory imagery was studied using magnetoencephalography. Trained musicians were presented with visual notes and instructed to imagine the corresponding sounds. Brain activity specific to the auditory imagery task was observed, first as enhanced activity of left and right occipital areas (average onset 120–150 ms after the onset of the visual stimulus) and then spreading to the midline parietal cortex (precuneus) and to such extraoccipital areas that were not activated during the visual control condition (e. g. , the left temporal auditory association cortex and the left and right premotor cortices). The latest activations, with average onset latencies of 270–400 ms clearly separate from the earliest ones, occurred in the left sensorimotor cortex and the right inferotemporal visual association cortex. These data imply a complex temporospatial activation sequence of multiple cortical areas when musicians recall firmly established audiovisual associations.

YNIMG Journal 2002 Journal Article

Modulated Activation of the Human SI and SII Cortices during Observation of Hand Actions

• Sari Avikainen
• Nina Forss
• Riitta Hari

Neurons in area F5 of the monkey premotor cortex are activated during both execution and observation of hand actions. A similar “mirror-neuron system” seems to exist also in the human brain, including at least the superior temporal sulcus region, Broca's area, and the primary motor cortex. We recorded somatosensory evoked fields in response to median nerve stimulation from nine healthy subjects during (i) rest, (ii) manipulation of a small object, and (iii) observation of the same action to find out to what extent the somatosensory cortices display behavior similar to the human mirror-neuron system. SI signals were enhanced and SII signals suppressed during both manipulation and observation, except when the right manipulating hand was stimulated. Our results suggest that the SI and SII cortices contribute to the human mirror-neuron system, possibly providing information necessary for preserving the sense of self during action observation.

YNIMG Journal 2002 Journal Article

Visually Evoked Gamma Responses in the Human Brain Are Enhanced during Voluntary Hyperventilation

• Ole Jensen
• Riitta Hari
• Kai Kaila

Hypocapnia induced by hyperventilation (HV) has powerful effects on neuronal excitability and synaptic transmission. We have studied the effect of hyperventilation on the phase-locked oscillatory components of the evoked responses in the human brain. We recorded visually evoked magnetoencephalographic responses before, during, and after voluntary hyperventilation to pattern-reversal checkerboard stimuli. Gamma-band (30–45 Hz) responses phase-locked to the stimuli were generated in the occipital visual cortex. A wavelet-based time-frequency analysis revealed that the gamma responses increased during HV whereas their frequency did not change significantly. A recent in vitro study in the rat hippocampus demonstrated that the stability of spontaneous gamma activity increases during hypocapnia as a result of enhanced GABAergic transmission. To test if a similar mechanism could account for our findings, we performed simulations on a network of 100 Hodgkin–Huxley neurons connected by inhibitory synapses. We found that enhanced GABA A transmission, paired with enhanced excitability, can explain the increase in evoked gamma activity without changing the frequency.

YNIMG Journal 2001 Journal Article

Binaural interaction revealed using frequency-tagged amplitude-modulated tones

• Nobuya Fujiki
• Veikko Jousma'Nki
• Riitta Hari

YNIMG Journal 2001 Journal Article

Oscillatory Interaction between Human Motor Cortex and Trunk Muscles during Isometric Contraction

• Nobuki Murayama
• Yung-Yang Lin
• Stephan Salenius
• Riitta Hari

We investigated oscillatory interaction between magnetoencephalographic signals of the human motor cortex and surface electromyogram from the paraspinal (PS) and abdominal (ABD) muscles. The results were compared with data obtained during contraction of the first dorsal interosseus (FDI) and tibialis anterior (TA) muscles. Significant coherence at 15–35 Hz was observed for both PS and ABD muscles in all subjects but the coherence was weak compared with that for FDI and TA. The cortical sources for both the PS and the ABD coherences were located in the motor cortex between the source areas for the FDI and TA coherences, thereby agreeing with the classical trunk area of the motor homunculus previously determined by invasive studies. The sources were strictly contralateral for PS but bilateral for ABD contractions. Our results indicate that during isometric contractions descending motor commands are modulated by cortical oscillations for both limb and trunk muscles, although the modulation is weaker and may be bilateral for trunk muscles.

YNIMG Journal 2001 Journal Article

Sign language and mirror neuron system

• Nobuyuki Nishitani
• Riitta Hari

YNIMG Journal 2001 Journal Article

Sustained Activation of the Human SII Cortices by Stimulus Trains

• Nina Forss
• Livio Narici
• Riitta Hari

To compare the functional properties of neurons in the human primary (SI) and secondary (SII) cortices, we recorded somatosensory-evoked fields (SEFs) from seven healthy subjects to single electric stimuli and stimulus trains delivered to the median nerve at 8–12 Hz. The SI and SII cortices responded strikingly differently to stimulus trains: whereas SI followed each stimulus with a sharp transient response up to at least 12 Hz, the transient responses were much less prominent at SII, which mainly responded with a sustained field that returned to baselevel at 800–1000 ms. The different response patterns of SI and SII suggest that the inhibition, following the early excitatory responses, is weaker at SII than SI, or that inhibitory responses of these two areas differ in their relative timing.

YNIMG Journal 2000 Journal Article

Abnormal Reactivity of the ∼20-Hz Motor Cortex Rhythm in Unverricht Lundborg Type Progressive Myoclonus Epilepsy

• Teija Silén
• Nina Forss
• Ole Jensen
• Riitta Hari

The ∼20-Hz component of the human mu rhythm originates predominantly in the primary motor cortex. We monitored with a whole-scalp neuromagnetometer the reactivity of the ∼20-Hz rhythm as an index of the functional state of the primary motor cortex in seven patients suffering from Unverricht–Lundborg type (ULD) progressive myoclonus epilepsy (PME) and in seven healthy control subjects. In patients, the motor cortex rhythm was on average 5 Hz lower in frequency and its strength was double compared with controls. To study reactivity of the ∼20-Hz rhythm, left and right median nerves were stimulated alternately at wrists. In controls, these stimuli elicited a small transient decrease, followed by a strong increase (“rebound”) of the ∼20-Hz level. In contrast, the patients showed no significant rebounds of the rhythm. As the ∼20-Hz rebounds apparently reflect increased cortical inhibition, our results indicate that peripheral stimuli excite motor cortex for prolonged periods in patients with ULD.

YNIMG Journal 2000 Journal Article

Coupling of human cortical and spinal motoneuron activity studied by simultaneous magneto- and electroencephalographic recordings

• Stephan Salenius
• Riitta Hari

YNIMG Journal 2000 Journal Article

Differential Effects of Muscle Contraction from Various Body Parts on Neuromagnetic Somatosensory Responses

• Yung-Yang Lin
• Cristina Simões
• Nina Forss
• Riitta Hari

We studied eight healthy subjects with a whole-scalp 306-channel neuromagnetometer to explore the effect of motor activity from different body parts on somatosensory responses to left median nerve stimulation. The stimuli produced clear tactile sensation without any motor movement. In the rest condition, the subject had no task. During contraction conditions, the subject had to maintain submaximal isometric contraction in masseter, left deltoid, left thenar, or left tibialis muscles. Short-latency responses from the primary somatosensory cortex did not change during contraction. Responses from both the right (contralateral) and left second somatosensory cortices (SII) were significantly enhanced during contraction of the left thenar muscles. Responses from the left SII were significantly enhanced also during contraction of the left deltoid muscles, but they were decreased during contraction of the masseter and left tibialis anterior muscles. This study implies that SII activation is modulated by motor activity and that the effect depends on the topographical proximity of the stimulated and contracted body parts.

YNIMG Journal 2000 Journal Article

Presurgical localization of sensorimotor cortex: comparison of fMRI, MEG and intraoperative cortical mapping

• Antti Korvenoja
• Erika Kirveskari
• Hannu J. Aronen
• Sari Avikainen
• Antti Brander
• Nina Forss
• Riitta Hari
• Juha Huttunen

YNIMG Journal 1999 Journal Article

Ipsilateral Movement-Evoked Fields Reconsidered

• Riitta Hari
• Toshiaki Imada

The generation mechanism of movement-evoked fields (MEFs) is poorly known and the existence of ipsilateral MEFs is still in dispute. We recorded whole-scalp neuromagnetic activity from eight subjects who were pressing response keys alternately with the right 2nd and 4th digits, while keeping the left palm on the table containing the keys. Clear ipsilateral MEFs peaked 58 ± 2 ms after the key touch, with sources in the hand area of the right primary somatosensory cortex. The ipsilateral MEFs decreased to half size when the resting left hand was palm up on the table. However, very similar responses were obtained when another person operated the response keys and the subjects just kept their left palm on the table. No signals were elicited when the subjects only viewed these actions with no hand contact to the table. The results indicate that the MEFs receive a strong contribution from tactile input. In our experiment the ipsilateral sensorimotor activation was triggered by the movement-related vibrations transmitted to the resting hand.

YNIMG Journal 1998 Journal Article

ICA for the Extraction of Auditory Evoked Fields

• Jaakko Särelä
• Ricardo Vigário
• Veikko Jousmäki
• Riitta Hari
• Erkki Oja

NeurIPS Conference 1997 Conference Paper

Independent Component Analysis for Identification of Artifacts in Magnetoencephalographic Recordings

• Ricardo Vigário
• Veikko Jousmäki
• Matti Hämäläinen
• Riitta Hari
• Erkki Oja

We have studied the application of an independent component analysis (ICA) approach to the identification and possible removal of artifacts from a magnetoencephalographic (MEG) recording. This statistical tech(cid: 173) nique separates components according to the kurtosis of their amplitude distributions over time, thus distinguishing between strictly periodical signals, and regularly and irregularly occurring signals. Many artifacts belong to the last category. In order to assess the effectiveness of the method, controlled artifacts were produced, which included saccadic eye movements and blinks, increased muscular tension due to biting and the presence of a digital watch inside the magnetically shielded room. The results demonstrate the capability of the method to identify and clearly isolate the produced artifacts.

YNIMG Journal 1997 Journal Article

Involvement of Primary Motor Cortex in Motor Imagery: A Neuromagnetic Study

• Alfons Schnitzler
• Stephan Salenius
• Riitta Salmelin
• Veikko Jousmäki
• Riitta Hari

Functional brain imaging studies have indicated that several cortical and subcortical areas active during actual motor performance are also active during imagination or mental rehearsal of movements. Recent evidence shows that the primary motor cortex may also be involved in motor imagery. Using whole-scalp magnetoencephalography, we monitored spontaneous and evoked activity of the somatomotor cortex after right median nerve stimuli in seven healthy right-handed subjects while they kinesthetically imagined or actually executed continuous finger movements. Manipulatory finger movements abolished the poststimulus 20-Hz activity of the motor cortex and markedly affected the somatosensory evoked response. Imagination of manipulatory finger movements attenuated the 20-Hz activity by 27% with respect to the rest level but had no effect on the somatosensory response. Slight constant stretching of the fingers suppressed the 20-Hz activity less than motor imagery. The smallest possible, kinesthetically just perceivable finger movements resulted in slightly stronger attenuation of 20-Hz activity than motor imagery did. The effects were observed in both hemispheres but predominantly contralateral to the performing hand. The attempt to execute manipulatory finger movements under experimentally induced ischemia causing paralysis of the hand also strongly suppressed 20-Hz activity but did not affect the somatosensory evoked response. The results indicate that the primary motor cortex is involved in motor imagery. Both imaginative and executive motor tasks appear to utilize the cortical circuitry generating the somatomotor 20-Hz signal.

YNIMG Journal 1997 Journal Article

Modulation of Human Cortical Rolandic Rhythms during Natural Sensorimotor Tasks

• Stephan Salenius
• Alfons Schnitzler
• Riitta Salmelin
• Veikko Jousmäki
• Riitta Hari

We studied modulation of cortical neuromagnetic rhythms in association with left and right median nerve stimulation, during rest, finger movements, and passive tactile hand stimulation, in seven healthy, right-handed adults. In the rest condition, the amplitude of the rhythmic sensorimotor activity decreased immediately after the median nerve stimuli and increased above the prestimulus level within 0. 4 s afterward, especially in the 7- to 25-Hz band. The rebound occurred 100–300 ms earlier for 20 (7–15)- than for 10 (15–25)-Hz activity. Suppressions and rebounds were strongest in the contralateral sensorimotor hand area for the 20-Hz, but not for the 10-Hz, activity. The maximum rebound was on average 22–34% stronger in the left than in the right hemisphere. Active exploration of objects abolished rebounds of both 10- and 20-Hz signals in the contralateral hemisphere and markedly diminished them ipsilaterally. Finger movements without touching an object and passive tactile stimulation produced a weaker effect. The sensorimotor rhythms thus show a characteristic suppression and subsequent rebound after electrical median nerve stimulation. The rebound is left-hemisphere dominant in right-handed subjects and its suppression reveals bilateral cortical activation during both motor tasks and passive tactile stimulation, especially for explorative finger movements.