Dynamics of coding and representation of temporal information in bat auditory cortex and midbrain

之前的项目集中在对回声延迟时间敏感的皮质神经元在回声定位蝙蝠中的功能作用。该项目的主要成果之一是证明了只有在使用自然的呼叫-回声序列作为刺激时，皮质抑制机制才能显著增强颞叶神经元的调谐。当使用孤立和随机呈现的呼叫-回声对作为刺激时，就像之前的许多研究中的情况一样，皮质反应更强，但特异性要低得多。这些结果相当新颖，强调了不仅使用与行为相关的刺激，而且使用刺激序列而不是孤立的声音事件来研究皮质功能的重要性。在这个延长项目中，我们旨在通过(I)研究中脑对自然序列的反应来研究序列特异性处理的机制。这应该有助于确定在大脑皮层观察到的时间性尖锐反应的第一个出现点。后者对于理解沿上升听觉通路发生的变化非常重要，并且使蝙蝠能够有效地从回声定位流中提取信息：(Ii)在皮质内，将使用电流源密度分析来评估层对序列处理的特定贡献，以及(Iii)我们将分析通过微离子导入GABA能和谷氨酸能药物来抑制刺激增强的突触机制。这一延长项目研究的结果应有助于对皮层抑制在处理和侧重于声序列中与物种有关的信息要素方面的作用进行总体评估。

The preceding project focussed on the functional role of cortical neurons that are sensitive for echo-delay time in echolocating bats. One of the main results of the project was the demonstration that the temporal neuronal tuning is sharpened considerably by a cortical suppression mechanism that only acts when natural call-echo sequences are used as stimuli. When isolated and randomly presented call-echo pairs are used as stimuli, as it was the case in many previous studies, the cortical responses are stronger but much less specific. These results are quite novel and emphasize the importance of using not only behaviorally relevant stimuli but stimulus sequences rather than isolated sound events to study cortical function. In this elongation project we aim to investigate the mechanisms of sequence-specific processing by (i) studying midbrain responses to natural sequences. This should help to define the first emergence point of the temporally sharp responses observed in the cortex. The latter is important for understanding the transformations that occur along the ascending auditory pathway and that enable bats to effectively extract information from echolocation streams (ii) Within the cortex, layer-specific contributions to sequence processing will be assessed using a current-source density analysis, and (iii) we will analyse synaptic mechanisms that play a role for a stimulus-enhancing suppression by microiontophoresis of GABAergic and glutaminergic pharmaca. The results of this elongation project study should contribute to a general assessment of the role of cortical suppression for processing and focusing on species-relevant information elements in acoustic sequences.