Discrimination between concurrent activities in the somatosensory cortex via topographic neuromagnetic investigation

A procedure is presented which is aimed at enhancing the functional localizing capability of the somatosensory neuromagnetic investigation. The procedure, which can be implemented automatically, in several cases makes it possible to distinguish the continuation of the firing of an activated source from the onset of the firing of a different one. The study focuses on medium-latency (40-80 ms) somatosensory responses under median nerve stimulation at the wrist. The temporal behavior of the equivalent sources as referred to the sources themselves is studied, and it is shown that for tens of milliseconds the activated region is quite stable in space while undergoing a smooth phase inversion. At longer latencies (after 70 ms), another activity seems to prevail. The same activity is found at a shorter latency, concurrent with the previous one