Audiovocal behavior of Doppler-shift compensation in the horseshoe bat survives bilateral lesion of the paralemniscal tegmental area.

Abstract

The role of the paralemniscal tegmental area of the horseshoe bat, Rhinolophus rouxi, in the control of vocalization and Doppler-shift compensation was investigated using electrical and pharmacological stimulation and lesioning techniques. The paralemniscal tegmental area is situated in the dorsolateral tegmentum ventral to the inferior colliculus and rostral and medial to the dorsal and intermediate nuclei of the lateral lemniscus. Vocalizations indistinguishable from spontaneously uttered calls can be elicited with both electrical and pharmacological stimulation methods, demonstrating that the stimulation of neural elements within the area and not fibers passing through the area are responsible for the stimulated call emission. The audiovocal feedback system for Doppler-shift compensation was also investigated. Doppler-shift compensation adjusts the frequency of the emitted calls according to the increases in the frequency of the echoes that are normally encountered in flying bats. Bats compensate for Doppler shifts not only under natural conditions but also when echoes are played back to the bat following spontaneous vocalizations or vocalizations induced by electrical or pharmacological stimulation of the investigated brain area. Unilateral electrolytic lesions of the paralemniscal tegmental area did not impair the ability to evoke vocalizations with electrical stimulation of the unlesioned side. The calls had exactly the same structure and frequency composition as those emitted prior to lesioning. Unilateral lesions also did not impair Doppler-shift compensation performance. After bilateral lesioning of the paralemniscal area, vocalizations could not be evoked with electrical stimulation. However, normal calls were emitted spontaneously and Doppler-shift compensation during spontaneous call emission was unaltered compared with the intact condition. The paralemniscal tegmental area is therefore not an audiovocal feedback system required for Doppler-shift compensation, but rather a brain area whose stimulation and activation is sufficient but not necessary for call emission. It is also not directly involved in the control of spectral parameters of vocalization but contributes to the control of the occurrence of vocal output.