One line of research at The Center for Neuromagnetism deals with the localization and monitoring of neuronal networks underlying cognition. Using magnetoencephalography we can determine the spatio-temporal pattern of coherent oscillatory neural activity correlated with different functional states and cognitive processes in real time. Magnetic recordings from humans in the awake and in rapid-eye-movement (REM) sleep states, revealed spontaneous coherent brain activity within the gamma band (~40 Hz) . This activity was absent or strongly reduced during delta sleep. Such coherent brain activity was shown to be reset or modified by sensory stimulation in the awake state only. Thus, waking and dreaming, the two general states that generate cognitive contents, are both associated with global coherent brain activity oscillating at the same frequency.

Magnetic field tomography, a noninvasive technique based on distributed source analysis of magnetoencephalography data, was used to visualize a spatiotemporally organized pattern of recurrent 40 Hz activity during auditory processing, and indicated a coherence of various elements oscillating at around 40 Hz within thalamocortical systems. Moreover, these 40 Hz thalamocortical oscillations were altered in pathological states such as Alzheimer's disease. These results suggest that coherent 40 Hz activity is part of a neural correlate underlying various cognitive processes.

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, MRI, 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.