Calling song recognition in female crickets: temporal tuning of identified brain neurons matches behavior

Phonotactic orientation of female crickets is tuned to the temporal pattern of the male calling song. We analyzed the phonotactic selectivity of female crickets to varying temporal features of calling song patterns and compared it with the auditory response properties of the ascending interneuron AN1 (herein referred to as TH1-AC1) and four newly identified local brain neurons. The neurites of all brain neurons formed a ring-like branching pattern in the anterior protocerebrum that overlapped with the axonal arborizations of TH1-AC1. All brain neurons responded phasically to the sound pulses of a species-specific chirp. The spike activity of TH1-AC1 and the local interneuron, B-LI2, copied different auditory patterns regardless of their temporal structure. Two other neurons, B-LI3 and B-LC3, matched the temporal selectivity of the phonotactic responses but also responded to some nonattractive patterns. Neuron B-LC3 linked the bilateral auditory areas in the protocerebrum. One local brain neuron, B-LI4, received inhibitory as well as excitatory synaptic inputs. Inhibition was particularly pronounced for nonattractive pulse patterns, reducing its spike activity. When tested with different temporal patterns, B-LI4 exhibited bandpass response properties; its different auditory response functions significantly matched the tuning of phonotaxis. Temporal selectivity was established already for the second of two sound pulses separated by one species-specific pulse interval. Temporal pattern recognition in the cricket brain occurs within the anterior protocerebrum at the first stage of auditory processing. It is crucially linked to a change in auditory responsiveness during pulse intervals and based on fast interactions of inhibition and excitation.