Processing of sound signals by six types of neurons in the prothoracic ganglion of the cricket,Gryllus campestris L.

Summary

• 1. Six types of auditory neurons, arranged as mirror-image pairs, were characterized intracellularly within the prothoracic ganglion.

• 2. Two of the six neuron types are restricted to the prothoracic ganglion and exhibit an omegashaped structure (Fig. 2, ON1, ON2). Two other neuron types have axons ascending to the head ganglion (Fig. 2, AN1, AN2). A neuron with a descending axon (Fig. 2, DN1) and a T-shaped neuron (Fig. 2, TN) having both an ascending and a descending axon were also characterized.

• 3. Physiologically, these neuron types are characterized by their suprathreshold responses in the range of 2–20 kHz (Fig. 3), by the time course of epsps (Figs. 4 and 5), and by their responses related to monaural and binaural input (Fig. 6). ON1 is excited by the ear ipsilateral to the cell body and inhibited from the opposite ear (Fig. 6). AN1 and DN1 receive only excitatory input from the ear contralateral to the cell body (Fig. 6). ON2 and TN receive excitatory input from both ears (Fig. 6). Ipsilateral stimulation of AN2 at the calling song frequency results in a response ranging from weak excitation to strong inhibition; contralateral stimulation at moderate and high intensities is always excitatory, but can exhibit mixed excitation and inhibition (Figs. 6 and 7).

• 4. Artificial calling songs excite all six types of neurons. ON1, AN1, and DN1 copy both syllables and pauses more precisely than ON2, AN2, and TN.

• 5. All six neuron types copy the temporal sequence of calling songs containing syllables of 2.5 ms duration. Intersyllable pauses smaller than 5 ms are not copied by any of the neuron types (Fig. 8).

• 6. Artificial calling songs with a duty cycle of 50% (equal duration of syllable and pause) are phonotactically effective only when syllable intervals lie within the range of 20–60 ms. None of the neurons reported here are tuned specifically to this range (Fig. 9).