Short-latency median-nerve somatosensory-evoked potentials and induced gamma-oscillations in humans.
Recent studies have suggested that cortical gamma-oscillations are tightly linked with various forms of physiological activity. In the present study, the dynamic changes of intracranially recorded median-nerve somatosensory-evoked potentials (SEPs) and somatosensory-induced gamma-oscillations were animated on a three-dimensional MR image, and the temporal and spatial characteristics of these activities were analysed in 10 children being evaluated for epilepsy surgery. Visual and quantitative assessments revealed that short-latency SEPs and somatosensory-induced gamma-oscillations predominantly involved the post-central gyrus and less intensely involved the pre-central gyrus and the anterior parietal lobule. Formation of a dipole of N20 peak with opposite polarities across the central sulcus was well delineated in animation movies. High-frequency (100-250 Hz) somatosensory-induced gamma-oscillations emerged in the post-central gyrus at 13.6-17.5 ms after median-nerve stimulation, gradually slowed down in frequency around and below 100 Hz, and progressively involved the neighbouring areas. A substantial proportion of somatosensory-induced gamma-oscillations was initially phase-locked and the proportion of a non-phase-locked component gradually increased over time. The primary motor hand areas proven by cortical stimulation frequently coincided with the sites showing the largest N20 peak and the largest somatosensory-induced gamma oscillations. In vivo animation of SEPs and somatosensory-induced gamma oscillations both may be utilized to localize the primary sensory-motor hand area in pre-surgical evaluation. The dipole on SEPs is consistent with the previously accepted notion that the cortices along the central sulcus are activated. The high-frequency somatosensory-induced gamma-oscillations in the post-central gyrus may represent the initial neural processing for external somatosensory stimuli, whereas the subsequent lower-frequency oscillations might represent the reafferent cortical activity occurring in larger cortical networks.
Department of Pediatrics, Wayne State University, Detroit Medical Center, Detroit, MI, 48201, USA.
Miho
M
Fukuda
Masaaki
M
Nishida
Csaba
C
Juhász
Otto
O
Muzik
Sandeep
S
Sood
Harry T
HT
Chugani
Eishi
E
Asano
D000293:Adolescent; D000328:Adult; D001931:Brain Mapping / Q000379:methods; D002648:Child; D002675:Child, Preschool; D004558:Electric Stimulation / Q000379:methods; D004569:Electroencephalography / Q000379:methods; D004827:Epilepsy / Q000503:physiopathology* / Q000601:surgery; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D007223:Infant; D008297:Male; D008475:Median Nerve / Q000503:physiopathology*; D011930:Reaction Time; D012815:Signal Processing, Computer-Assisted; D013003:Somatosensory Cortex / Q000503:physiopathology