RESUBMISSION: Neural processing underlying auditory pattern recognition in an insect brain

神经科学旨在了解感觉通路是如何组织的，刺激是如何处理的，以及如何提取特征以引起适当的运动反应。特别是在种内交流中，特定刺激特征的识别起着重要的作用，因为物种特异性的嗅觉、视觉和/或听觉信号被用于配偶吸引和竞争行为。由于声音总是短暂的，因此在许多脊椎动物和无脊椎动物中，通过重复的脉冲模式发出信号是声学通信的核心。特别是青蛙和昆虫，如蟋蟀和蟋蟀，使用简单的声音脉冲产生的物种特定的时间模式进行通信。在接收器的听觉通路中，这些信号需要响应声音模式的时间结构的神经过滤器机制。在描述大脑神经元对脉冲模式的选择性调谐方面，青蛙已经取得了相当大的进展。然而，仍然有一个非常有限的了解神经元的基本时间处理的声音模式，蟋蟀，虽然几十年来，他们是一个模型系统的昆虫听力。雌性蟋蟀被特定种类的雄性叫声所吸引。在行为实验中，我们展示了它们的声定向行为的调谐脉冲间隔，脉冲持续时间和啁啾间隔的变化。例如，它们的趋声行为被调谐到男性歌曲的脉冲模式，因为周期较短或较长的脉冲没有吸引力。我们现在的目标是在已识别神经元的水平上了解大脑中允许识别物种特异性歌曲模式的过滤机制，将呼叫歌曲的脉冲模式从第一胸神经节转发到大脑的上行听觉中间神经元没有表现出过滤特性。人们提出了脑中存在时间滤波的假说，但其具体的神经机制尚未得到揭示。在初步的实验中，我们确定了局部脑神经元，形成一个环状的听觉神经元在前脑匹配的轴突分支的上行中间神经元。这些神经元中的一些表现出选择性反应的脉冲间隔的呼叫歌曲，并接受抑制性和兴奋性突触输入。在其他系统中，抑制和兴奋之间的相互作用对于脉冲模式的选择性至关重要。使用相同的声学范式，在行为研究中，我们将分析听觉脑神经元的活动。我们将重点讨论四个问题：（1）。哪些脑神经元参与了声脉冲模式的时间滤波？2）。时间滤波背后的神经机制是什么？3）。听觉神经元的结构和功能组织是什么？4）。哪些投射神经元将听觉神经元连接到其他大脑区域？该项目将基于我们用尖锐的微电极记录细胞内听觉脑神经元活动的经验。神经反应将与我们的行为数据进行比较，定量分析将揭示单个神经元的活动在多大程度上反映了行为调整。抑制性和兴奋性突触活动的模式将提供关于听觉网络内如何实现时间滤波的关键信息。我们将通过细胞内电流注入来操纵神经元的膜电位，以详细分析神经过滤机制的性质。最后，我们将使用共聚焦显微镜来揭示这些神经元在大脑中的结构细节，我们将识别将听觉神经元与大脑其他区域联系起来的神经元。蟋蟀的模式识别网络的分析将提供洞察力的原则机制的时间过滤在确定的神经元的水平，并可以在其他系统的时间选择性的模型。

Neuroscience aims at understanding how sensory pathways are organised, how stimuli are processed and how features are extracted to elicit an appropriate motor response. Especially in intraspecific communication the recognition of specific stimulus features plays an important role as species-specific olfactory, visual and/or acoustic signals are employed for mate attraction and rivalry behaviour. As sounds are always transient, signalling by repetitive patterns of pulses is central to acoustic communication in many vertebrates and invertebrates. Especially frogs and insects like bush-crickets and crickets use simple sound pulses generated with species-specific temporal patterns for communication. In the auditory pathway of the receiver, these signals require neural filter mechanisms that respond to the temporal structure of sound patterns. Considerable progress has been made in frogs in describing brain neurons with selective tuning to pulse patterns. However, there is still a very limited understanding of neurons underlying temporal processing of sound patterns in crickets although since decades they are a model system for insect hearing. Female crickets are attracted to the species-specific pattern of male calling song. In behavioural experiments we demonstrated the tuning of their phonotactic behaviour to changes in pulse interval, pulse duration and chirp interval. For example their phonotactic behaviour is tuned to the pulse pattern of the male song as pulses with shorter or longer periods are not attractive. We now aim to understand at the level of identified neurons the filter mechanisms in the brain that allow the recognition of the species-specific song pattern.The ascending auditory interneuron that forwards the pulse pattern of the calling song from the first thoracic ganglion to the brain exhibits no filter properties. Hypothesis for temporal filtering in the brain have been put forward, however, the actual neural mechanisms have not been revealed. In preliminary experiments we identified local brain neurons which form a ring-like auditory neuropil in the protocerebrum matching the axonal arborisations of the ascending interneuron. Some of these neurons showed a selective response to the pulse interval of the calling song and received inhibitory and excitatory synaptic inputs. In other systems the interaction between inhibition and excitation is crucial for selectivity to pulse patterns. Using the same acoustic paradigms as in the behavioural studies we will analyse the activity of auditory brain neurons. We will focus on four questions: 1). Which brain neurons are involved in temporal filtering of acoustic pulse patterns?2). What are the neural mechanisms underlying temporal filtering? 3). What is the structural and functional organisation of the auditory neuropil?4). Which projection neurons connect the auditory neuropil to other brain regions?The project will be based on our experience of recording intracellularly the activity of auditory brain neurons with sharp microelectrodes. The neural responses will be compared with our behavioural data and quantitative analysis will reveal to what degree the activity of single neurons mirrors the behavioural tuning. The pattern of inhibitory and excitatory synaptic activity will provide crucial information on how temporal filtering is achieved within the auditory network. We will manipulate the membrane potential of neurons by intracellular current injection to analyse the nature of the neural filter mechanisms in detail. Finally we will use confocal microscopy to reveal the structural details of these neurons in the brain and we will identify neurons which link the auditory neuropil to other areas of the brain. The analysis of the pattern recognition network in crickets will provide insight to principle mechanisms of temporal filtering at the level of identified neurons and can be a model for temporal selectivity in other systems.