Chantal E. Stern

YNIMG Journal 2022 Journal Article

Theta oscillations support active exploration in human spatial navigation

• Elizabeth R. Chrastil
• Caroline Rice
• Mathias Goncalves
• Kylie N. Moore
• Syanah C. Wynn
• Chantal E. Stern
• Erika Nyhus

Active navigation seems to yield better spatial knowledge than passive navigation, but it is unclear how active decision-making influences learning and memory. Here, we examined the contributions of theta oscillations to memory-related exploration while testing theories about how they contribute to active learning. Using electroencephalography (EEG), we tested individuals on a maze-learning task in which they made discrete decisions about where to explore at each choice point in the maze. Half the participants were free to make active decisions at each choice point, and the other half passively explored by selecting a marked choice (matched to active exploration) at each intersection. Critically, all decisions were made when stationary, decoupling the active decision-making process from movement and speed factors, which is another prominent potential role for theta oscillations. Participants were then tested on their knowledge of the maze by traveling from object A to object B within the maze. Results show an advantage for active decision-making during learning and indicate that the active group had greater theta power during choice points in exploration, particularly in midfrontal channels. These findings demonstrate that active exploration is associated with theta oscillations during human spatial navigation, and that these oscillations are not exclusively related to movement or speed. Results demonstrating increased theta oscillations in prefrontal regions suggest communication with the hippocampus and integration of new information into memory. We also found evidence for alpha oscillations during active navigation, suggesting a role for attention as well. This study finds support for a general mnemonic role for theta oscillations during navigational learning.

YNIMG Journal 2016 Journal Article

Entorhinal volume, aerobic fitness, and recognition memory in healthy young adults: A voxel-based morphometry study

• Andrew S. Whiteman
• Daniel E. Young
• Andrew E. Budson
• Chantal E. Stern
• Karin Schon

Converging evidence supports the hypothesis effects of aerobic exercise and environmental enrichment are beneficial for cognition, in particular for hippocampus-supported learning and memory. Recent work in humans suggests that exercise training induces changes in hippocampal volume, but it is not known if aerobic exercise and fitness also impact the entorhinal cortex. In animal models, aerobic exercise increases expression of growth factors, including brain derived neurotrophic factor (BDNF). This exercise-enhanced expression of growth hormones may boost synaptic plasticity, and neuronal survival and differentiation, potentially supporting function and structure in brain areas including but not limited to the hippocampus. Here, using voxel based morphometry and a standard graded treadmill test to determine cardio-respiratory fitness (Bruce protocol; ·VO2 max), we examined if entorhinal and hippocampal volumes were associated with cardio-respiratory fitness in healthy young adults (N =33). In addition, we examined if volumes were modulated by recognition memory performance and by serum BDNF, a putative marker of synaptic plasticity. Our results show a positive association between volume in right entorhinal cortex and cardio-respiratory fitness. In addition, average gray matter volume in the entorhinal cortex, bilaterally, was positively associated with memory performance. These data extend prior work on the cerebral effects of aerobic exercise and fitness to the entorhinal cortex in healthy young adults thus providing compelling evidence for a relationship between aerobic fitness and structure of the medial temporal lobe memory system.

YNICL Journal 2015 Journal Article

Altered intrinsic functional coupling between core neurocognitive networks in Parkinson's disease

• Deepti Putcha
• Robert S. Ross
• Alice Cronin-Golomb
• Amy C. Janes
• Chantal E. Stern

Parkinson's disease (PD) is largely attributed to disruptions in the nigrostriatal dopamine system. These neurodegenerative changes may also have a more global effect on intrinsic brain organization at the cortical level. Functional brain connectivity between neurocognitive systems related to cognitive processing is critical for effective neural communication, and is disrupted across neurological disorders. Three core neurocognitive networks have been established as playing a critical role in the pathophysiology of many neurological disorders: the default-mode network (DMN), the salience network (SN), and the central executive network (CEN). In healthy adults, DMN-CEN interactions are anti-correlated while SN-CEN interactions are strongly positively correlated even at rest, when individuals are not engaging in any task. These intrinsic between-network interactions at rest are necessary for efficient suppression of the DMN and activation of the CEN during a range of cognitive tasks. To identify whether these network interactions are disrupted in individuals with PD, we used resting state functional magnetic resonance imaging (rsfMRI) to compare between-network connectivity between 24 PD participants and 20 age-matched controls (MC). In comparison to the MC, individuals with PD showed significantly less SN-CEN coupling and greater DMN-CEN coupling during rest. Disease severity, an index of striatal dysfunction, was related to reduced functional coupling between the striatum and SN. These results demonstrate that individuals with PD have a dysfunctional pattern of interaction between core neurocognitive networks compared to what is found in healthy individuals, and that interaction between the SN and the striatum is even more profoundly disrupted in those with greater disease severity.

YNIMG Journal 2015 Journal Article

Functional connections between optic flow areas and navigationally responsive brain regions during goal-directed navigation

• Katherine R. Sherrill
• Elizabeth R. Chrastil
• Robert S. Ross
• Uğur M. Erdem
• Michael E. Hasselmo
• Chantal E. Stern

Recent computational models suggest that visual input from optic flow provides information about egocentric (navigator-centered) motion and influences firing patterns in spatially tuned cells during navigation. Computationally, self-motion cues can be extracted from optic flow during navigation. Despite the importance of optic flow to navigation, a functional link between brain regions sensitive to optic flow and brain regions important for navigation has not been established in either humans or animals. Here, we used a beta-series correlation methodology coupled with two fMRI tasks to establish this functional link during goal-directed navigation in humans. Functionally defined optic flow sensitive cortical areas V3A, V6, and hMT+ were used as seed regions. fMRI data was collected during a navigation task in which participants updated position and orientation based on self-motion cues to successfully navigate to an encoded goal location. The results demonstrate that goal-directed navigation requiring updating of position and orientation in the first person perspective involves a cooperative interaction between optic flow sensitive regions V3A, V6, and hMT+ and the hippocampus, retrosplenial cortex, posterior parietal cortex, and medial prefrontal cortex. These functional connections suggest a dynamic interaction between these systems to support goal-directed navigation.

YNIMG Journal 2014 Journal Article

Theta rhythm and the encoding and retrieval of space and time

• Michael E. Hasselmo
• Chantal E. Stern

Physiological data demonstrates theta frequency oscillations associated with memory function and spatial behavior. Modeling and data from animals provide a perspective on the functional role of theta rhythm, including correlations with behavioral performance and coding by timing of spikes relative to phase of oscillations. Data supports a theorized role of theta rhythm in setting the dynamics for encoding and retrieval within cortical circuits. Recent data also supports models showing how network and cellular theta rhythmicity allows neurons in the entorhinal cortex and hippocampus to code time and space as a possible substrate for encoding events in episodic memory. Here we discuss these models and relate them to current physiological and behavioral data.

YNIMG Journal 2012 Journal Article

Cooperative interactions between hippocampal and striatal systems support flexible navigation

• Thackery I. Brown
• Robert S. Ross
• Sean M. Tobyne
• Chantal E. Stern

Research in animals and humans has demonstrated that the hippocampus is critical for retrieving distinct representations of overlapping sequences of information. There is recent evidence that the caudate nucleus and orbitofrontal cortex are also involved in disambiguation of overlapping spatial representations. The hippocampus and caudate are functionally distinct regions, but both have anatomical links with the orbitofrontal cortex. The present study used an fMRI-based functional connectivity analysis in humans to examine the functional relationship between the hippocampus, caudate, and orbitofrontal cortex when participants use contextual information to navigate well-learned spatial routes which share common elements. Participants were trained outside the scanner to navigate virtual mazes from a first-person perspective. Overlapping condition mazes began and ended at distinct locations, but converged in the middle to share some hallways with another maze. Non-overlapping condition mazes did not share any hallways with any other maze. Successful navigation through the overlapping hallways required contextual information identifying the current navigational route to guide the appropriate response for a given trial. Results revealed greater functional connectivity between the hippocampus, caudate, and orbitofrontal cortex for overlapping mazes compared to non-overlapping mazes. The current findings suggest that the hippocampus and caudate interact with prefrontal structures cooperatively for successful contextually dependent navigation.

YNIMG Journal 2011 Journal Article

An fMRI investigation of the fronto-striatal learning system in women who exhibit eating disorder behaviors

• Kim A. Celone
• Heather Thompson-Brenner
• Robert S. Ross
• Elizabeth M. Pratt
• Chantal E. Stern

In the present study, we sought to examine whether the fronto-striatal learning system, which has been implicated in bulimia nervosa, would demonstrate altered BOLD activity during probabilistic category learning in women who met subthreshold criteria for bulimia nervosa (Sub-BN). Sub-BN, which falls within the clinical category of Eating Disorder Not Otherwise Specified (EDNOS), is comprised of individuals who demonstrate recurrent binge eating, efforts to minimize their caloric intake and caloric retention, and elevated levels of concern about shape, weight, and/or eating, but just fail to meet the diagnostic threshold for bulimia nervosa (BN). fMRI data were collected from eighteen women with subthreshold-BN (Sub-BN) and nineteen healthy control women group-matched for age, education and body mass index (MC) during the weather prediction task. Sub-BN participants demonstrated increased caudate nucleus and dorsolateral prefrontal cortex (DLPFC) activation during the learning of probabilistic categories. Though the two subject groups did not differ in behavioral performance, over the course of learning, Sub-BN participants showed a dynamic pattern of brain activity differences when compared to matched control participants. Regions implicated in episodic memory, including the medial temporal lobe (MTL), retrosplenial cortex, middle frontal gyrus, and anterior and posterior cingulate cortex showed decreased activity in the Sub-BN participants compared to MCs during early learning which was followed by increased involvement of the DLPFC during later learning. These findings demonstrate that women with Sub-BN demonstrate differences in fronto-striatal learning system activity, as well as a distinct functional pattern between fronto-striatal and MTL learning systems during the course of implicit probabilistic category learning.

YNIMG Journal 2008 Journal Article

Delayed match to object or place: An event-related fMRI study of short-term stimulus maintenance and the role of stimulus pre-exposure

• Karin Schon
• Sule Tinaz
• David C. Somers
• Chantal E. Stern

Recent delayed matching studies have demonstrated that maintaining trial-unique stimuli in working memory modulates activity in temporal lobe structures. In contrast, most previous studies that focused on the role of the prefrontal cortex (PFC) used familiar stimuli. We combined fMRI with a delayed-match-to-sample (DMS) task in humans that allowed us to manipulate stimulus pre-exposure (trial-unique vs. familiar objects) and stimulus domain (object vs. location). A visually guided saccade task was used to localize the frontal eye fields (FEF). We addressed two questions: First, we examined whether delay-period activity within PFC regions was more strongly engaged when stimuli were familiar (pre-exposed) than when they were not seen previously (trial-unique). Second, we examined the role of regions within the PFC in object vs. location working memory. Subjects were instructed to remember one stimulus domain while ignoring the other over an 8-s delay period. Object-specific delay-period activity was greatest in the posterior orbitofrontal cortex (OFC) bilaterally, and was stronger for familiar than trial-unique objects. In addition, consistent with previous findings, right posterior superior frontal sulcus, and the FEF were specifically active during the delay period of the location DMS task. These activations outside FEF were not related to saccadic eye movements. In contrast to previous reports, object-specific delay activity was more prominent in the posterior OFC than in the ventrolateral PFC, and was found to be greater for familiar than for trial-unique objects. These results suggest a critical role for the orbitofrontal cortex for maintaining object information in working memory.

YNIMG Journal 2007 Journal Article

Mental rotation and object categorization share a common network of prefrontal and dorsal and ventral regions of posterior cortex

• Haline E. Schendan
• Chantal E. Stern

The multiple-views-plus-transformation variant of object model verification theories predicts that parietal regions that are critical for mental rotation contribute to visual object cognition. Some neuroimaging studies have shown that the intraparietal sulcus region is critically involved in mental rotation. Other studies indicate that both ventral and dorsal posterior regions are object-sensitive and involved in object perception and categorization tasks. However, it is unknown whether dorsal object-sensitive areas overlap with regions recruited for object mental rotation. Functional magnetic resonance imaging was used to test this directly. Participants performed standard tasks of object categorization, mental rotation, and eye movements. Results provided clear support for the prediction, demonstrating overlap between dorsal object-sensitive regions in ventral–caudal intraparietal sulcus (vcIPS) and an adjacent dorsal occipital area and the regions that are activated during mental rotation but not during saccades. In addition, object mental rotation (but not saccades) activated object-sensitive areas in lateral dorsal occipitotemporal cortex (DOT), and both mental rotation and object categorization recruited ventrolateral prefrontal cortex areas implicated in attention, working memory, and cognitive control. These findings provide clear evidence that a prefrontal–posterior cortical system implicated in mental rotation, including the occipitoparietal regions critical for this spatial task, is recruited during visual object categorization. Altogether, the findings provide a key link in understanding the role of dorsal and ventral visual areas in spatial and object perception and cognition: Regions in occipitoparietal cortex, as well as DOT cortex, have a general role in visual object cognition, supporting not only mental rotation but also categorization.

YNIMG Journal 2000 Journal Article

Activity in Ventrolateral and Mid-Dorsolateral Prefrontal Cortex during Nonspatial Visual Working Memory Processing: Evidence from Functional Magnetic Resonance Imaging

• Chantal E. Stern
• Adrian M. Owen
• Irene Tracey
• Rodney B. Look
• Bruce R. Rosen
• Michael Petrides

Whole-brain functional magnetic resonance imaging was used to study five healthy human subjects while they performed two nonspatial visual working memory tasks and one control task. In the first memory task, the subjects were required to view a sequence of three pattern stimuli, randomly selected from a familiar set of four stimuli, and then identify which one of three simultaneously presented stimuli was the one that had not been presented in the previous array. In the other task, the subjects were required to observe an identical sequence of three randomly selected pattern stimuli and then to respond by selecting those same stimuli in the order presented. In comparison to a baseline control task, increases in signal intensity were observed, bilaterally, in the mid-dorsolateral frontal cortex and in the right ventrolateral frontal cortex in both memory tasks. When the two tasks were compared directly, however, the first memory task, which had the higher monitoring requirement, yielded significantly greater signal intensity changes in area 9/46 of the right mid-dorsolateral frontal cortex. These results provide further evidence for the precise functional contribution made by the mid-dorsolateral frontal cortex in visual working memory tasks and concur closely with findings in nonhuman primates.

YNIMG Journal 2000 Journal Article

Prefrontal and medial temporal lobe roles in long-term vs. short-term stimulus matching

• Seth J. Sherman
• Brenda A. Kirchhoff
• Michael E. Hasselmo
• Chantal E. Stern

YNIMG Journal 1998 Journal Article

Monitoring Selections from a Visual Array Activates the Mid-dorsolateral Frontal Cortex: Evidence from Functional MRI

• Chantal E. Stern
• Adrian M. Owen
• Rodney B. Look
• Irene Tracey
• Bruce R. Rosen
• Michael Petrides