An Acridid Auditory Interneurone

Abstract

The alpha neurone habituates to repetitive short (40 msec.) or long (2–3 sec.) pulses of sound. The response decrement to 10 short pulses at 1/sec. is exponential. Twenty-five minutes is required for complete recovery to 20 short pulses at 1/sec. No dishabituation followed various changes in stimulus repetition. The C.N.S. affects both response level and habituation. In 13% of all animals the neurone was completely inhibited by the head ganglia and was disinhibited by decapitation. Progressive lesions reveal strong inhibition by the head ganglia, and possibly weaker inhibition by the abdominal chain; the prothoracic ganglion has no apparent effect. Removal of the head ganglia almost halves the habituation rate; further removal of the abdominal chain may give a further slight reduction; the prothoracic ganglion has no effect. There is a significant negative correlation between response level and habituation. This could be partially explained if the absolute response decrement is independent of response level. The remaining decrease in habituation observed suggests either a further link between response level and habituation at the synapse, or possibly independent central control of both. Central control affects habituation more than response level. Spontaneous variation in response level is unaffected by the various central lesions. It thus arises in the posterior thoracic ganglia, and not as descending inhibition or excitation from higher centres. These findings are related to the animal’s biology and to previous work.