Far field somatosensory potentials in the rat.

Averaged somatosensory evoked potentials (SEPs) in the rat were recorded from skull electrodes. The cortical component of the SEP was preceded by at least three low amplitude potentials. Surface distribution of these potentials, correlation with depth recording from posterior columns, posterior column nuclei, inferior cerebellar peduncle, medial lemniscus, ventral posterior thalamus and sensory radiation, and the effect of brain stem and medullospinal transections on these potentials showed that: (1) All potentials preceding the cortical SEP are far field reflections of activity generated at a distance from the site or recording. (2) Component I originates in posterior columns. (3) Component II reflects summated activities in posterior column nuclei and medial lemniscus. (4) Anterior component III reflects summated activities in the ventral posterior thalamus and sensory radiation. (5) Posterior component III probably reflects activities originating in cerebellar pathways and cerebellum.