Short-latency median-nerve somatosensory-evoked potentials and induced gamma-oscillations in humans

Abstract

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.

Gamma-Band Oscillations in the Primary Somatosensory Cortex—A Direct and Obligatory Correlate of Subjective Pain Intensity

“…However, the possibility that GBOs reflect cortical activity that is specific for the processing of somatosensory input, but not specific for the processing of nociceptive input should not be dismissed. Indeed, several studies have shown that non-nociceptive somatosensory stimuli also elicit GBOs within SI (Chen and Herrmann, 2001;Bauer et al, 2006;Fukuda et al, 2008). Hence, nociceptive and non-nociceptive somatosensory GBOs could reflect similar cortical responses, involved in the initial selection and preferential processing of somatosensory stimuli regardless of whether they are nociceptive.…”

Neuromagnetic investigations of mechanisms and effects of STN-DBS and medication in Parkinson's disease

“…Inspection of the data showed clear N20m and induced activity in beta as well as low and high gamma bands as also previously reported (Fukuda et al, 2008(Fukuda et al, , 2010Hagiwara et al, 2010). Lack of effects of treatments on N20m is in line with previous results (Pierantozzi et al, 1999;Priori et 4.3 Study II al., 2001;Conte et al, 2010;Airaksinen et al, 2011) although some of these earlier studies may be partly confounded by methodological issues.…”

“…Median nerve stimulation and the subsequent oscillatory dynamics such as somatosensory evoked fields (SEF) or potentials (SEP) are effective tools to study somatosensory processing (Gaetz and Cheyne, 2003;Fukuda et al, 2008Fukuda et al, , 2010. Median nerve stimulation involves placing a bipolar stimulation electrode near the wrist, where the median nerve runs superficially and stimulating it with a current of 2-15 mA and with a pulse width of 150 μ s. The sign of a stimulated nerve is a visible twitch of the thumb.…”

“…Gamma oscillations in general have been found to modulate the synchrony in local excitatory activity and is seen as an index of cortical computation (Fries, 2009). Gamma oscillations that were recorded in rat somatosensory cortex (SI & SII) were not global but restricted to somatosensory areas (MacDonald and Barth, 1995), and in humans, short latency power increases found in broadband gamma power (40-100 Hz) were confined to contralateral S1 (Hirata et al, 2002;Ihara et al, 2003;Gaetz and Cheyne, 2006;Fukuda et al, 2008Fukuda et al, , 2010.…”

“…Hence, early gamma augmentation in somatosensory cortex can be considered an early aspect of somatosensory information processing (Fukuda et al, 2008(Fukuda et al, , 2010, mainly produced by excitatory pyramidal neurons within temporal windows created by inhibitory interneurons. Modulation of the amplitudes of such gamma augmentations might reflect recruitment of additional neuronal populations or increased precision in synchronization (Srinivasan et al, 1999).…”