COMPARISON OF VOLUME-CONDUCTED FAR-FIELD SHORT-LATENCY GLOSSOPHARYNGEAL NERVE EVOKED-POTENTIALS RECORDED FROM THE SCALP WITH SIMILARLY OBTAINED NEAR-FIELD POTENTIALS FROM THE SOLITARY NUCLEUS IN DOGS

In 11 dogs, potentials recorded from the scalp and from the solitary n ucleus after stimulation of the glossopharyngeal nerve were compared. The far-field potentials recorded from the scalp consisted of negativi ty, with peak latency of 2.10 to 3.45 milliseconds (mean, 2.93 millise conds), followed by positivity, with peak latency of 3.20 to 5.95 mill iseconds (mean, 4.86 milliseconds) and duration of 4.65 to 6.95 millis econds (mean, 5.70 milliseconds). The near-field potentials recorded f rom the solitary nucleus consisted of positivity, with peak latency of 2.15 to 2.70 milliseconds (mean, 2.45 milliseconds), followed by nega tivity,with peak latency of 4.05 to 5.05 milliseconds (mean, 4.39 mill iseconds) and duration of 4.45 to 5.80 milliseconds (mean, 5.21 millis econds). Comparison of the far-field potentials (n = 10) with the near -field potentials (n = 5) indicated that polarity of the waves was rev ersed and that the first peak's latency was slightly (approx 0.5 milli seconds) longer in the scalp-recorded far-field potentials. Neither th e difference in latency of the second peak nor the difference in its d uration, measured from the onset of the potentials to the return to th e baseline of the activity, was significant. The results strongly sugg est that the response in the solitary nucleus evoked by electrical. st imulation of the glossopharyngeal nerve is the source of at least part of the scalp-recorded responses to stimulation of the same nerve. The scalp-recorded far-field potentials could, therefore, be characterize d as volume conducted from the evoked response in the solitary nucleus .