Differential generators for N20m and P35m responses to median nerve stimulation.
To study the spatial and behavioral dynamics of cortical sources for N20m and P35m at varying stimulus intensities, we measured neuromagnetic cortical responses to left electric median nerve stimulation at the wrist in 17 male healthy adults. The stimulus intensity levels were individually determined according to sensory threshold (ST) for perceiving electric pulses. Using equivalent current dipole (ECD) modeling, we analyzed the peak latencies, amplitudes, and locations of ECDs from 14 subjects for N20m and P35m elicited at 2 ST, 3 ST, and 4 ST. Compared with N20m, P35m was localized 3.3 +/- 0.6 mm more superiorly at 2-4 ST, and 2.9 +/- 1.2 mm more medially at 3-4 ST. Superimposed over subjects' own MR images, N20m ECDs were localized in the area of 3b contralateral to stimulus side in all 17 subjects at 3 ST, whereas P35m ECDs were localized either in the postcentral (in 14 subjects) or in the precentral areas (in 3 subjects). We found no clear correlation between N20m and P35m in terms of peak latencies as well as the corresponding growth of activation strengths along with stepwise increase in stimulus intensity. Our results imply that the two early SEF components, N20m and P35m, have differential cortical generators, with distinctive neurophysiological behaviors in response to varying stimulus intensity levels.
Lin
Yung-Yang
YY
Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei, Taiwan. yylin@vghtpe.gov.tw
Chen
Wei-Ta
WT
Liao
Kwong-Kum
KK
Yeh
Tzu-Chen
TC
Wu
Zin-An
ZA
Ho
Low-Tone
LT
Lee
Liang-Shong
LS
D000328:Adult; D002540:Cerebral Cortex / Q000502:physiology*; D004558:Electric Stimulation; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography; D008297:Male; D008475:Median Nerve / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology; D014953:Wrist / Q000294:innervation / Q000502:physiology