Far-field somatosensory evoked potentials in the cat: correlation with depth recording

We have previously identified, with surface-recording techniques, four potentials (I, II, III, IV) preceding the cortical component of the somatosensory evoked potential (SEP) in the cat. In the present study, we correlated surface and depth activity in the cat by recording SEPs simultaneously from skull electrodes and from depth electrodes placed in the cervical posterior columns, cuneate nucleus, medial lemniscus, inferior cerebellar peduncle, ventral posterior thalamus, and sensory radiation. Latencies and amplitudes of surface- and depth-recorded potentials and their responses to repetitive stimulation were analyzed. Our findings indicate that: (1) component I originates in cervical posterior columns and nucleus cuneatus; (2) component II reflects postsynaptic activity in nucleus cuneatus, medial lemniscus, and inferior cerebellar peduncle; (3) component III-A probably originates in the cerebellar hemispheres; (4) component III-B consists of component III-A and superimposed activity in the ventral posterior thalamus and sensory radiation; and (5) component IV originates in the sensory radiation.