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Tomás Ortiz

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4 papers

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YNIMG Journal 2011 Journal Article

The correlation between white-matter microstructure and the complexity of spontaneous brain activity: A difussion tensor imaging-MEG study

Alberto Fernández
Marcos Ríos-Lago
Daniel Abásolo
Roberto Hornero
Juan Álvarez-Linera
Nuria Paul
Fernando Maestú
Tomás Ortiz

The advent of new signal processing methods, such as non-linear analysis techniques, represents a new perspective which adds further value to brain signals' analysis. Particularly, Lempel–Ziv's Complexity (LZC) has proven to be useful in exploring the complexity of the brain electromagnetic activity. However, an important problem is the lack of knowledge about the physiological determinants of these measures. Although a correlation between complexity and connectivity has been proposed, this hypothesis was never tested in vivo. Thus, the correlation between the microstructure of the anatomic connectivity and the functional complexity of the brain needs to be inspected. In this study we analyzed the correlation between LZC and fractional anisotropy (FA), a scalar quantity derived from diffusion tensors that is particularly useful as an estimate of the functional integrity of myelinated axonal fibers, in a group of sixteen healthy adults (all female, mean age 65. 56±6. 06years, intervals 58–82). Our results showed a positive correlation between FA and LZC scores in regions including clusters in the splenium of the corpus callosum, cingulum, parahipocampal regions and the sagittal stratum. This study supports the notion of a positive correlation between the functional complexity of the brain and the microstructure of its anatomical connectivity. Our investigation proved that a combination of neuroanatomical and neurophysiological techniques may shed some light on the underlying physiological determinants of brain's oscillations.

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YNIMG Journal 2005 Journal Article

Is medial temporal lobe activation specific for encoding long-term memories?

Pablo Campo
Fernando Maestú
Tomás Ortiz
Almudena Capilla
Santiago Fernández
Alberto Fernández

Several neuroimaging studies have consistently demonstrated the critical involvement of prefrontal cortices and medial temporal lobes during long-term encoding. While the contribution of prefrontal lobes to working memory is well established, the role of the MTL structures remains controversial. To address this issue, we registered the neuromagnetic brain patterns of eight adult volunteers while they performed two working memory tasks (verbal and spatial) using magnetoencephalography (MEG). MEG recordings can provide real-time measures of brain activity, thus allowing detailed tracking of the time-course of brain activation during the encoding phase. We detected sustained and material-specific activity on the MTLs during the encoding phase of a working memory task, based on verbal and spatial information. Two peaks of activation were noted in the left MTL during word encoding in two non-consecutive time periods (500–600 ms and 700–800 ms after stimulus onset). Right MTL laterality was found for encoding locations when we collapsed activity sources in a wider time period (400–800 ms). In addition, we provided the spatiotemporal profiles of what seems to be two different brain circuits specific for each type of material. Finally, following an emerging conceptualization of working memory, we hypothesized that encoding processes mediated by the MTL to long-term memory would also apply to working memory.

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YNIMG Journal 2003 Journal Article

Modulation of brain magnetic activity by different verbal learning strategies

Fernando Maestú
Panagiotis G Simos
Pablo Campo
Alberto Fernández
Carlos Amo
Nuria Paul
Javier González-Marqués
Tomás Ortiz

In this study we examined spatiotemporal profiles of brain activity in the context of tasks designed to engage different verbal learning strategies (serial order, phonological, and semantic). The profile of activation associated with the serial-order strategy, which resulted in poor recall performance, featured early activation of the inferior frontal, sensorimotor, and insular region in the left hemisphere, between 200 and 400 ms after stimulus onset. Subsequently, activation was more prominent in dorsolateral prefrontal cortices bilaterally. In contrast, activation profiles associated with the phonological strategy featured predominantly activation of the superior temporal gyrus in the left hemisphere between 500 and 600 ms. Predominant activation of the left middle temporal gyrus, between 500 and 700 ms, was the key feature of the activation profile observed when the semantic elaboration strategy was utilized. These results suggest that different brain circuits are engaged to support learning of new verbal information as a function of the level and type of initial processing applied to the stimuli.

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YNIMG Journal 2002 Journal Article

Spanish Language Mapping Using MEG: A Validation Study

Fernando Maestú
Tomás Ortiz
Alberto Fernandez
Carlos Amo
Pilar Martin
Santiago Fernández
Rafael G. Sola

The purpose of the present study was to compare magnetoencephalography (MEG) data with the results of the intracarotid amytal procedure (IAP). Twenty-one native Spanish-speaking patients with intractable epilepsy underwent MEG language mapping. A subset of 8 patients also underwent an IAP. With the exception of 2 patients who showed right hemisphere dominance, all other patients showed left hemisphere dominance for language on the MEG recording. The IAP findings were consistent with MEG results in 7 patients. The eighth patient who, according to the MEG data, had probable right hemisphere dominance for language did not show clear hemispheric specialization for language on the IAP and suffered a transient global aphasia following a right temporal lobotomy. These results suggests that MEG-based language mapping can play an important role in presurgical clinical evaluation.

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