Inter-areal Coupling of Human Brain Function

With the recent advance of modern technologies applicable for non-invasive investigation of human brain functions, 'localization' or 'specialization' of various functions in the cerebral cortices as well as in the subcortical structures has been elucidated in normal subjects, especially in the last 10 years.

These technologies include analysis of electroencephalogram (EEG) and magnetoencephalogram (MEG), transcranial magnetic stimulation (TMS), blood flow activation studies using positron emission tomography (PET) and single photon emission computed tomography (PET), and functional magnetic resonance imaging (fMRI). The findings from these non-invasive investigations, in association with information obtained from clinical observation of patients with localized cerebral lesions (lesion studies), have greatly contributed to the understanding of higher human brain functions. Activation studies, however, often demonstrate multiple areas, not only cerebral cortices but also including subcortical structures, being activated almost at the same time. Therefore, it has become increasingly important to elucidate the functional relationship among different areas, and eventually the neuronal network or circuitry including the information about the direction of circuit flow.