Coding of sinusoidally amplitude modulated acoustic stimuli in the inferior colliculus of the rufous horseshoe bat, Rhinolophus rouxi.

Single neuron responses to sinusoidally amplitude modulated (SAM) signals were studied in the inferior colliculus of the horseshoe bat, Rhinolophus rouxi. 57% of the neurons responded to SAM stimuli with periodical discharges synchronized to the modulation cycle. The proportion of cells driven by amplitude modulated signals was independent of the best frequency of the neurons. Best modulation frequencies were at or below 100 Hz in about 70% of the neurons. Synchronized activity could be elicited by modulation frequencies up to 400 Hz. Best SAM responses were observed at stimulus intensities 10 dB above threshold. Generally the BMF of a neuron did not change with intensity. The BMF decreased with decreasing modulation depth of the amplitude modulation. A trend for a topographical organization of neurons according to best modulation frequencies was detected. The results did not reveal any significant specialization of the bat's auditory system for coding of amplitude modulations as compared to other mammals.