Regularity increases middle latency evoked and late induced beta brain response following proprioceptive stimulation

Focal attention increases the middle-latency amplitude of somatosensory evoked potentials. Previously this effect has been suggested to be due to increased readiness in somatosensory cortex. Presently, we examine whether regularity of stimulus occurrence increases the proprioceptive evoked response as an indication of increased readiness. This is achieved through detailed analysis of both evoked and induced responses in the time-frequency domain. Electroencephalography in a 64 channels montage was recorded in fourteen healthy subjects. Two paradigms were explored: A Regular alternation between hand of presentation and a Random sequence of hand of presentation. The ERPWAVELAB toolbox was used for decomposition of the wavelet transformed data (7 to 47 Hz, -300 to +1500 ms)" yielding the evoked amplitude (AvWT) and inter-trial phase coherence as well as the increase of non-time-locked activity (Induced). After initial exploration of the AvWT and Induced collapsed files of all subjects using two-way factor analyses (Non-Negative Matrix Factorization), further data decomposition was performed in restricted windows of interest (WOI). Main effects of side of stimulation, onset or offset, regularity and habituation on the evoked and induced activity are described for each WOI. The Regular paradigm evoked more activity than Random in the fast beta range (18-28 Hz) (mean: normalized amplitude 0.38 at 90 ms and 20.9 Hz) including increased phase precision. The findings confirm the possibility of modulation of middle-latency activity by regularity and suggest that this is due to facilitation of activity in secondary somatosensory cortices. Future studies need to examine whether the increased amplitude is associated with increased perceptual acuity.