Neurophysiological investigations into the human somatosensory system

Using noninvasive neuroimaging methods in human subjects, we attempt to understand functional neuroanatomy and neurophysiological processes (somatotopy, inhibition, excitation, spike bursts, background activity) underlying somatosensory function. In order to define functional neuroanatomy, we use mainly task-based fMRI to identify somatotopy e.g., in SI and SII. Recently, we showed that gross somatotopy can also be extracted from task-less resting-state fMRI. Regarding neurophysiological processes, we show that the strength of background rhythms (Rolandic alpha, beta rhythm) determines receptiveness of the somatosensory system to activation and is inversely related to cortical BOLD-fMRI signal. We establish a model of predominant inhibitory processing using subliminal stimulation and we show that this decreases BOLD-fMRI signal, decreases connectivity of SI, and transiently increases alpha rhythm. Using simultaneous EEG-fMRI, we identify correlates of spike bursts in human subjects non-invasively and relate them to BOLD fMRI signal along the path of somatosensory processing.