TOPOGRAPHY AND SOURCES OF ELECTROMAGNETIC CEREBRAL RESPONSES TO ELECTRICAL AND AIR-PUFF STIMULATION OF THE HAND

SEPs and SEFs after air-puff stimulation of index and little fingers h ave been studied and compared to the responses following electrical st imulation of the same digits and of the median nerve at the wrist in 5 subjects. The differences in morphology of the evoked signals are des cribed and the generator characteristics are analysed for SEFs by mean s of a moving dipole model inside a homogeneous sphere. In our measure ments the magnetic fields following electrical finger stimulation show a 30 msec component, which was absent following air-puff stimulation. This could not be seen in the electric field activity. The generators of the first component of SEFs after air-puff finger stimulation prov ed to be deeper (8 mm on average across all subjects and for both fing ers) than in the case of electrically evoked SEFs. A similar behaviour was also observed for the second component of SEFs for the 2 stimulus modalities.