The neural basis of active echo imaging

回声定位蝙蝠可以通过对其声纳发射的回声进行听觉分析来定位和识别三维物体。回波的频谱-时间结构不仅取决于反射对象的声学特性，而且还取决于发射的特性。回声成像需要对发射和回声进行详细的比较。以前的生理学研究只在麻醉、被动倾听的动物身上研究回声成像的神经基础。这与在发声和主动倾听动物身上获得行为反应的心理物理学工作形成了鲜明对比。这项提议旨在结合这些方法来研究主动回声成像中的神经处理。将使用两种不同的方法：在一组实验中，通过电微刺激在清醒蝙蝠的下降发声系统的大脑旁区域诱发回声定位叫声。使用来自行为幻影-目标工作的技术，3D对象的声音图像被实时印在呼叫上，并以合成回声的形式回放。该技术允许系统地处理与对象相关的声学信息。听觉皮质神经元对呼叫和合成回声的反应都将被记录下来。通过比较有和没有发声的神经元的反应，可以揭示蝙蝠发声对神经处理的影响。在第二种方法中，听觉皮质神经元的反应将用长期植入的电极记录在自由活动的蝙蝠身上。蝙蝠将接受心理物理辨别任务的训练，当蝙蝠执行任务时，神经反应将通过一个小型遥测系统传输。通过这种方法，可以洞察蝙蝠表现背后的神经活动。

Echolocating bats can localize and identify three dimensional objects through the auditory analysis of the echoes of their sonar emissions. The spectro-temporal structure of an echo depends not only on the acoustical properties of the reflecting object, but also on the properties of the emission. Echo imaging requires the detailed comparison of the emission and echo. Previous physiological studies investigated the neural basis of echo imaging only in anaesthetized, passively listening animals. This contrasts to the psychophysical work where behavioral responses were obtained in vocalizing and actively listening animals.This proposal aims to combine these approaches to investigate neural processing in active echo imaging. Two different approaches will be used: in one set of experiments echolocation calls will be evoked by electrical microstimulation in an area of the descending vocalization system, the paralemniscal area, in awake bats. Using the techniques from behavioral phantom-target work, the acoustic images of 3D objects are imprinted on the calls in real-time and played back as synthetic echoes. This technique allows to systematically manipulating object-related acoustic information. The responses from neurons in the auditory cortex to both the call and the synthetic echo will be recorded. By comparing the response of a neuron with and without previous vocalization, the effect of the bat’s vocalization on neural processing can be revealed. In a second approach the responses from neurons in auditory cortex will be recorded with chronically implanted electrodes in freely moving bats. The bats will be trained in a psychophysical discrimination task and the neural responses will be transmitted with a small telemetric system while the bats are performing the task. With this approach insight in the neural activity underlying the bats performance will be gained.