P 105 Spatio-temporal characteristics of somatosensory-evoked high-gamma activity of the EEG

Abstract

Introduction There is enlarging interest in the cortical function of high gamma band (HGB) changes related to different sensory modalities, movement tasks, and higher cognitive processes. EEG experiments have shown visually-evoked, auditory-evoked, and movement-related HGB changes, including the range of 50–70 Hz ( Tallon-Baudry et al., 1997 , Ball et al., 2008 ). While HGB activity in this frequency range associated to peripheral somatosensory stimulation was reported for intracranial recordings in neurological patients ( Fukuda et al., 2008 ), it has received little attention in EEG studies. Here the focus was on very high frequency somatosensory responses above 600 Hz ( Curio et al., 1994 ). In the present study, we implemented an experimental setup, optimized to measure high frequencies in the EEG, to investigate if robust 50–70 Hz HGB activity in noninvasive EEG could be identified during median nerve SEP stimulation and what the spatio-temporal characteristics of these changes are. Methods In an electromagnetically-shielded cabin, EEG data of 15 healthy subjects was obtained with 128 Ag/AgCl scalp electrodes and with NeurOne amplifiers (24-bit digital resolution and 5 kHz sampling rate). 1200 SEPs per subject were evoked by stimulation of the left median nerve with a SEP-stimulator. Simultaneous eye-tracking data from 7 of these subjects was attained to examine the influence of ocular movements on the neuronal recordings. Data analysis included preprocessing, short-time Fourier transformation algorithm, normalization, calculation of induced and evoked responses and a false discovery rate corrected sign test. Results All analyzed subjects showed a significant spectral power increase in the HGB range at 50–70 Hz after median nerve stimulation ( p Conclusion Using our purpose-build experimental set up, we were able to demonstrate a specific contralateral somatosensory-evoked response pattern in the 50–70-Hz frequency range of the noninvasive EEG. Our results agree with the findings of previous intracranial SEP studies and open up new possibilities to noninvasively study sensory related brain functions, both in healthy subjects and neurological patients.