| Summary: | This study involved investigations into the neural processing of auditory information by the Australian field cricket Teleogryllus oceanicus in relation to the identification of its conspecific songs. T. oceanicus males produce three song types related to three different behavioural strategies. Although each of the three songs have very similar frequency spectra their temporal patterns are very different and highly complex, particularly the courtship song. Song type recognition therefore is likely to be based on neurones capable of producing an accurately coded response to the song patterns. Using extracellular and intracellular recording techniques, neurophysiological and neuroanatomical investigations were carried out in order to Identify auditory interneurones in the pro-thoracic ganglion capable of coding for the temporal patterns of the songs. Two examples of the ascending class of neurones were identified and shown to respond to the conspecific song patterns: ANC, which coded the temporal pattern of the calling song and ANA, which produced a correlated response to the temporal pattern of the courtship song. Further investigations showed that as a result of the frequency content, syllable rate and intensity of the song, it was the Integration of excitatory and particularly inhibitory Inputs that allowed ANA to code for the courtship song. To identify other neurones involved in this pathway the origin of the inhibitory input was investigated. The local bilateral omega neurone, ONI, was thought to mediate the inhibition. Current manipulation experiments which involved simultaneous extracellular and intracellular recordings from ANA and ONI respectively were carried out. However, these experiments showed no evidence for the existence of effective synapses between these two cells. A second type of omega neurone was identified, ON2. Although this neurone was shown to be non-spiking its response was correlated with the temporal patterns of the songs. Preliminary investigations were carried out on examples of descending and through neurones.
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