Brain Advance Access originally published online on May 27, 2008
Brain 2008 131(7):1793-1805; doi:10.1093/brain/awn100
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Short-latency median-nerve somatosensory-evoked potentials and induced gamma-oscillations in humans
1Department of Pediatrics, 2Department of Neurology, 3Department of Radiology, 4Department of Neurosurgery and 5Department of Electroneurodiagnostics, Children's Hospital of Michigan, Wayne State University, Detroit Medical Center, Detroit, MI 48201, USA
Correspondence to: Eishi Asano, MD, PhD, MS (CRDSA), Division of Pediatric Neurology, Children's Hospital of Michigan, Wayne State University, 3901 Beaubien St., Detroit, MI, 48201, USA E-mail: eishi{at}pet.wayne.edu
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.
Key Words: electrical brain stimulation; functional brain mapping; in vivo animation movie; pediatric epilepsy surgery; quantitative sub-dural electroencephalography (EEG) analysis
Abbreviations: ECoG, electrocorticography; FIR, finite impulse response; MEG, magnetoencephalography; SEPs, somatosensory-evoked potentials; TMS, transcranial magnetic stimulation; TSE, temporal spectral evolution
Received September 17, 2007. Revised April 22, 2008. Accepted May 1, 2008.
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