Two evoked responses with different recovery functions in the primary somatosensory cortex in humans.
OBJECTIVE
We investigated the recovery function of somatosensory evoked magnetic cortical fields (SEFs) to confirm the temporal aspects of the somatosensory process in humans.


METHODS
SEFs were recorded following median nerve electrical stimulation in 6 healthy subjects. Double stimulation, with interstimulus intervals (ISIs) from 3 to 100 ms, was applied, and the SEF components for the second stimulation were analyzed. In a supplementary experiment, responses to single stimulations of various intensities from the sensory threshold to the motor threshold were studied.


RESULTS
The first SEF component (1M) diminished when the ISI was less than 10 ms, while the second component (2M) remained even when the ISI was 3 ms. The two components showed a very similar attenuation with decrease of stimulus intensity. There was no significant difference in dipole location between 1M and 2M in the primary somatosensory cortex (SI).


CONCLUSIONS
The results suggested that at least two independent pathways with different recovery functions exist in a similar area in the SI.
Hoshiyama
M
M
Department of Integrative Physiology, National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8585, Japan. hosiyama@nips.ac.jp
Kakigi
R
R
D000328:Adult; D001931:Brain Mapping; D004558:Electric Stimulation; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D008475:Median Nerve / Q000502:physiology; D009474:Neurons / Q000502:physiology; D013003:Somatosensory Cortex / Q000166:cytology / Q000502:physiology*