Interaction between afferent input from fingers in human somatosensory cortex.
We recorded somatosensory evoked magnetic fields from eight healthy subjects with a 122-channel whole-scalp SQUID magnetometer. The stimulus sequence consisted of 'standard' stimuli (85%) delivered to palmar side of the left thumb with an interstimulus interval of 0.6 s and of 'deviants' (15%), randomly interspersed among the standards, to little finger, and vice versa. Both stimuli activated four source areas: the contralateral primary somatosensory cortex (SI), the contra-and ipsilateral secondary somatosensory cortices (SII), and the contralateral posterior parietal cortex (PPC). The short-latency (20-40 ms) responses originated in the SI cortex, whereas long-latency responses arose from all 4 areas. At SII and PPC, the deviant stimuli elicited larger responses when presented alone, without intervening standards, than among standards. This implies interaction between afferent impulses from the two fingers and/or partly intermingled cortical representations. Our findings show, in agreement with animal data, different excitatory/inhibitory balance in the various somatosensory areas.
Forss
N
N
Low Temperature Laboratory, Helsinki University of Technology, Otakaari 3A, Espoo, Finland.
Jousmäki
V
V
Hari
R
R
D000328:Adult; D000344:Afferent Pathways / Q000502:physiology; D004558:Electric Stimulation; D004574:Electromagnetic Fields; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D005385:Fingers / Q000294:innervation*; D006801:Humans; D008297:Male; D010296:Parietal Lobe / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D012016:Reference Values; D013003:Somatosensory Cortex / Q000502:physiology*