Recovery function of short latency components of surface and depth recorded somatosensory evoked potentials in the cat.

Recovery functions of early components of surface and depth recorded somatosensory evoked potentials were studied in the cat. At interstimulus intervals of 50 msec or less differentiation of surface components was optimal. Component I showed less decrement at all ISI's than did component II and recovery curves of both were distinctly different from those of components III (anterior) and IV and the cortical SEP. The latter three potentials had similar recovery curves. Comparisons of latencies and recovery curves of surface recorded potentials with those of depth recorded potentials indicate that component I principally reflects activity in posterior column, that potentials in medial lemniscus, cuneate nucleus, and lateral cuneate nucleus contribute to component II, that the major generator for the contralateral component III is the ventral postero-lateral nucleus of the thalamus, and that component IV is largely due to activity in the sensory radiation. The results of this study support previous observations and conclusions about the origin of short latency, surface recorded somatosensory evoked potentials preceding the cortical SEP.