A comparison of forepaw and vibrissae somatosensory cortical evoked potentials in the rat

Somatosensory evoked potentials were elicited in anesthetized rats by electrical stimulation of the forepaw (F-SEP) or the vibrissae (V-SEP) and were compared in order to study which of these is a more valid animal model for studying the physiology and pathophysiology of somatosensory evoked potentials (SEPs) that are often recorded in man in a clinical setting. Intensity and rate functions were measured for the two potentials. The V-SEPs had larger amplitudes than the F-SEPs at high stimulus intensity and low stimulus rate. Furthermore, the ratios of the maximal amplitude of the F-SEP to that of the V-SEP (0.66) and of the areas under the curves of the two responses (0.75) reflected the smaller representation of the forepaw in the primary somatosensory cortex of the rat, compared to the vibrissae (ratio of cortical areas about 0.79). The differences should be taken into account when using median nerve SEP in the rat as a model of the human SEP. Study of V-SEPs in rat may provide insight into trigeminal nerve SEPs in man, which are also occasionally used for neurological evaluation.