Magnetoencephalography (MEG), a totally noninvasive functional imaging technique, allows localizing and monitoring of dynamic human brain functions in three-dimensions. Our various laboratory projects presently address the physiology of cognition. Additionally, new evidence has been obtained for the functional reorganization of human cortex and a better understanding of the underlying activity of various pathological human brain functions.

Over the past years various studies using magnetic recordings (MEG) have supported the hypothesis that cognitive activity is associated with gamma band (25 to 50Hz) oscillatory activity in the human brain. This activity, which arises from the intrinsic electrical properties of neurons and their recurrent network loops was found to be resetable, by sensory stimulation, at thalamo-cortical level. Earlier, we introduced the use of magnetic field tomography (MFT), a technique based on distributed source analysis of MEG data. Using MFT on humans, results indicated that the onset of gamma-band activity at the thalamic level was followed by widespread activation of the thalamocortical system, resulting in large coherent thalamocortical gamma oscillations organized in space and time and altered in pathological states such as Alzheimer disease.

We had further proposed that coherent patterns of thalamo-cortical oscillatory activity supports the temporal binding mechanism responsible for bringing together information from various sensory modalities into one single percept. Indeed, MEG recordings on control subjects demonstrated that such precise timing of thalamo-cortical network activity, originally described during auditory temporal processing, was also present in the somatosensory and visual modality in the healthy human brain.

MEG studies further provided evidence for a slight dysrhythmia within thalamo-cortical systems in subjects with Language-Based Learning Disabilities. Clearly an alteration of precise timing of thalamo-cortical networks correlated to altered behavioral patterns, namely to altered perception of sensory input. In unconscious humans, MEG and PET data indeed indicated a massive fracture of thalamo-cortical systems, as observed in persistent vegetative patients. These findings let us suggest that a dysrhythmia within thalamo-cortical systems could represent a key issue underlying various pathological behavioral symptoms. Recent MEG results, combined with findings based on electrical recordings from human thalamus and physiological findings on animals, indeed indicated that a severe and sustained dysrhythmia within thalamo-cortical systems could underlie various positive symptoms observed in a subset of neurological and psychiatric patients.