2月3日《神经科学杂志》（The Journal of Neuroscience）发表了神经科学研究所神经元信息处理和可塑性实验室关于听皮层的调频声音方向选择性形成的突触机制的最新发现。博士研究生叶昌泉通过对大鼠初级听皮层的在体膜片钳电生理研究，揭示初级听皮层的调频方向选择性建立的多重突触机制：包括声音激活的兴奋性突触输入的时间延迟在声音频率象限上有规律的变化；兴奋性和抑制性输入的感受野在声音频段上的差异分布，即不同频段声音差异性地激活抑制性和兴奋性输入。这项研究直接地验证了存在已久的感觉神经元方向性特征建立的通用突触机制模型，也为了解大脑感觉处理信息的工作机制提供了实验基础。
在自然环境中，许多声音都具有调频（frequency modulation）特性，即声音频率在一定的频谱范围内变化。这种声音频率在不同方向（如低频到高频的升频声音，或高频到低频的降频声音）、不同速率上变化的调频特征在动物和人类语音交流中普遍存在，并携带了重要的语音信息，为动物叫声和人类语言的识别提供了至关重要的特征信息。在大脑的听觉信息传递通路中，包括初级听觉皮层在内的一些功能核团的神经细胞表现出对声音频率变化（调频）方向的强选择性。这与视觉中枢中视觉神经细胞对物体移动方向的偏好性相类似。人们一直在探索是什么神经机制促使大脑感觉细胞表征这些外界信息中方向特征，进而来高效地编码和处理外界感觉信息。此项工作是在神经科学研究所章晓辉研究员课题组、蒲慕明研究员实验室和加利福尼亚大学伯克利分校丹扬教授的共同合作下完成，并受到中科院“创新项目”和科技部“973”项目“脑结构和功能的可塑性”的资助。（生物谷Bioon.com）
生物谷推荐原始出处：
The Journal of Neuroscience, February 3, 2010, 30(5):1861-1868; doi:10.1523/JNEUROSCI.3088-09.2010
Synaptic Mechanisms of Direction Selectivity in Primary Auditory Cortex
Chang-quan Ye,1 Mu-ming Poo,1,2 Yang Dan,2,3 and Xiao-hui Zhang1
1Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China, 2Division of Neurobiology, Department of Molecular and Cell Biology and Helen Wills Neuroscience Institute, University of California, Berkeley, California 94720, and 3Howard Hughes Medical Institute, University of California, Berkeley, California 94720
Frequency modulation (FM) is a prominent feature in animal vocalization and human speech. Although many neurons in the auditory cortex are known to be selective for FM direction, the synaptic mechanisms underlying this selectivity are not well understood. Previous studies of both visual and auditory neurons have suggested two general mechanisms for direction selectivity: (1) differential delays of excitatory inputs across the spatial/spectral receptive field and (2) spatial/spectral offset between excitatory and inhibitory inputs. In this study, we have examined the contributions of both mechanisms to FM direction selectivity in rat primary auditory cortex. The excitatory and inhibitory synaptic inputs to each cortical neuron were measured by in vivo whole-cell recording. The spectrotemporal receptive field of each type of inputs was mapped with random tone pips and compared with direction selectivity of the neuron measured with FM stimuli. We found that both the differential delay of the excitatory input and the spectral offset between excitation and inhibition are positively correlated with direction selectivity of the neuron. Thus, both synaptic mechanisms are likely to contribute to FM direction selectivity in the auditory cortex. Finally, direction selectivity measured from the spiking output is significantly stronger than that based on the subthreshold membrane potentials, indicating that the selectivity is further sharpened by the spike generation mechanism.
