The function of auditory neurons in cricket phonotaxis

SummaryIn order to examine the role of particular identified auditory neurons of the cricket,Gryllus bimaculatus, in orientation to a sound source, a method has been developed by which intracellular recordings can be made while the animal walks on an air-suspended sphere, which is rotated by the leg movements (Fig. 1). The angular velocities of sphere rotation were found to depend on the direction of incident sound, on its intensity and frequency and on the temporal pattern of the sound stimulus (Figs. 2, 3).While the cricket was walking, auditory neurons discharged extra action potentials, not correlated with the sound stimulus, and the neuronal response to the sound itself was reduced (Figs. 4, 5).Suppressing the spike activity by hyperpolarization of a local neuron in the prothoracic ganglion (ON1) reduced in some animals the tendency to turn toward the sound source on the side of the ear that excites the ON1 (Figs. 6–8). Hyperpolarization of a neuron that ascends from the prothoracic ganglion into the brain (AN1), while sound was presented to the ear that excites this neuron, caused all animals to reverse direction; that is, they turned away from the sound source and from the side of the inactivated AN1 (Figs. 9, 10). Hyperpolarization of another ascending neuron (AN2) caused a reduction in turning velocity in half of the animals; but this effect occurred only with high sound pressure levels, and the direction of walking was not reversed (Figs. 11, 12).From the influences on turning tendency observed in these experiments, it appears that the paired AN1s (and possibly the AN2s at high intensities) may provide inputs to a central comparator that dictates turning tendency in phonotaxis.