Time-frequency analysis of somatosensory potentials evoked by vibrotactile stimulation of the fingertip

Abstract

Tactile sensory feedback has become an essential topic for neural engineering to model advanced neuroprostheses providing artificial sensations. For this purpose, it is required to understand human brain activity related to some parameters (e.g., sensation level, frequency, time window, etc.) of tactile somatosensory inputs. There have been numerous studies related to tactile psychophysical channels and their prop erties. However, so far, a link could not be established between psychophysical data and somatosensory evoked potentials (SEPs) generated by vibrotactile stimulation in humans. Therefore, the fundamental goal of this study is to analyze SEPs, which were generated by 40 Hz vibrotactile stimulus applied to human fingertip, over the S1 cor tex. EEG data were collected and analyzed in a previous study by Yildiz (2013), but it was reanalyzed by different methods in this thesis. In particular, seven healthy adult subjects participated in psychophysical experiments. EEG recordings were obtained for several (NS, 10dB, 20dB, and 30dB) sensation levels (SLs) at and above threshold. They were collected at the forehead and Cpi-Cpc as mechanically evoked SEPs by gold surface EEG electrodes on the human scalp over the S1 cortex. The data were analyzed by Continuous Wavelet Transform (CWT) by means of Morse Wavelet at dif ferent time windows of stimulation. Consequently, no significant differences were found in frequency band energies for different sensation levels except some combinations in the low gamma band at the stimulus onset. Given the small sample size, these results imply that non-invasive EEG recording methods may not be adequate to measure fine psychophysical parameters in this study for flutter sensation at 40 Hz.|Keywords : tactile sensory feedback, tactile psychophysical channels, primary somatosensory cortex, somatosensory evoked potentials, morse wavelet, continuous wavelet transform.