Effects of somatosensory deafferentation on spectral characteristics of the sensorimotor EEG in the adult cat

A quantitative assessment of the sensorimotor EEG before and after transection of the dorsal columns at either a high (C1 to C3) or low (C5 to T1) cervical level was undertaken in unrestrained, adult cats. Electroencephalographic signals recorded unilaterally from postcruciate cortex (A:23) at medial (L:2 to 5) and lateral (L: 10 to 12) sites were subjected to bandpass frequency analysis. The incidence of 12- to 15-Hz sleep spindles and sensorimotor rhythm (SMR) activity was evaluated in comparable pre/postlesion EEG segments. Frequency analyses focused on the distribution of voltage in four bands (4 to 7, 8 to 11, 12 to 15, and 18 to 23 Hz). The findings showed that dorsal column transections markedly altered EEG spectral distributions. Most consistently affected was 8- to 15-Hz activity which increased significantly over sites corresponding to peripheral receptive fields below the level of the lesions. Observed increases in sleep spindles and SMR activity contributed to this finding. In prelesion recordings, voltage in all bands increased progressively over the course of slow-wave sleep to REM onset. Abrupt peaks in 12- to 15-Hz and 18- to 23-Hz activity preceded the REM stage. Dorsal column transections eliminated this sequence of frequency/voltage changes. These findings were interpreted in terms of the release of intrinsic rhythmic discharge patterns over ventrobasal thalamocortical projection pathways.