2 tone suppression of an identified auditory neuron in the brain of the cricket gryllus bimaculatus
Journal of Comparative Physiology A Sensory Neural & Behavioral Physiology 144(1): 117-126
An identified auditory neuron in the brain of the cricket G. bimaculatus (De Geer), the Plurisegmental auditory brain neuron 2 (PABN2), is susceptible to 2-tone suppression. Intracellular recordings of the PABN2 show that its best frequency (BF) as derived from the area of the compound EPSP is 13 kHz, near the conspecific courtship song frequency. When test tones (TT) of various frequencies between 1 and 11 kHz are added to a control tone (CT) of 15 kHz, 85 dB sound pressure level, the response of the PABN2 neuron is selectively suppressed. Frequencies of 4, 5 and 6 kHz are most effective in suppressing the response, frequencies centered on the conspecific calling song; those above and below are far less effective. The suppression is intensity-dependent and also operates for a CT of 10 kHz which is an harmonic component of the calling song. Latency of response is independent of the composition of the 2-tone complex. The suppression appears to be mediated presynaptically partly because no clear or hidden inhibitory postsynaptic potential can be detected, and unilaterally since occlusion of the contralateral ear does not alter the pattern or extent of the suppression. An hypothesis is proposed that a mechanism exists which, via the suppression of high frequency responses by the calling song, more clearly defines the information content of the calling and courtship songs for the female at close range.