Notes of the "frontal somatosensory generator". A preface to the article "Evidence for perirolandic generators of median nerve SEPs from differential scalp recording"
Abstract
Scalp somatosensory (SEP) P22/N30/P45 are non-constant waveforms evoked by stimulation of the median nerve, attributed to the frontal somatosensory generator. Transcortical, cortical, epidural and scalp recordings of evoked responses are discussed, demonstrating their generation in the rolandic fissure and the perirolandic region and their spreading as a remote response over the scalp, diminished and deformed by the high resistance of bone.
They counterbalance the constant somatosensory postrolandic response of the opposite polarity. It is argued that they do not represent a direct ,,motor" thalamocortical response.
There are no valid reasons for the hypothesis that abnormalities of ,,P22/N30/P45" are manifestations of extrapyramidal disorders. Bipolar scalp recordings presented in the accompanying paper confirm these facts