Somatosensory-evoked potential in clinically normal dogs.

Repetitive electrical peripheral nerve stimulation produces a multiphasic cerebrocortical potential termed the somatosensory-evoked potential (SEP). Scalp SEP recordings were made from 12 clinically normal dogs tranquilized with acepromazine. Three individual potentials were recognized in most SEP recordings and were identified as n1, p1, and n2. Additional positive potentials consistently followed n2, but their latencies and amplitudes varied considerably, so these waveforms were not numbered. They were termed late-positive potentials. Mean peak latencies +/- SD of the 3 potentials were determined to be 13.5 +/- 1.5 ms (n1), 19.6 +/- 2.7 ms (p1), and 43.3 +/- 10.4 ms (n2). The 1st negative deflection (n1) occurred between 11.0 and 16.0 ms after the stimulus and was consistently followed by a positive deflection (p1) which occurred at a latency ranging from 15.5 to 24.0 ms. The 2nd negative deflection (n2) occurred between 32.0 and 54.0 ms after the stimulus and was followed by a solitary prominent positive deflection or multiple positive potentials. Late-positive potential peak latencies ranged from 47.5 to 231.5 ms.