Institute of Neuroscience and State Key Laboratory of Neuroscience, Chinese Academy of Sciences, Shanghai 200031, China.
J Neurosci. 2010 Feb 3;30(5):1861-8. doi: 10.1523/JNEUROSCI.3088-09.2010.
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.
调频（FM）是动物发声和人类言语的一个显著特征。尽管听觉皮层中有许多神经元被认为对 FM 方向具有选择性，但这种选择性的突触机制尚不清楚。先前对视觉和听觉神经元的研究表明，方向选择性有两种一般机制：（1）兴奋输入在空间/频谱感受野上的差异延迟，（2）兴奋和抑制输入之间的空间/频谱偏移。在这项研究中，我们研究了这两种机制对大鼠初级听觉皮层中 FM 方向选择性的贡献。通过在体全细胞膜片钳记录测量了每个皮层神经元的兴奋性和抑制性突触输入。用随机音调脉冲映射每种输入的频谱时间感受野，并将其与用 FM 刺激测量的神经元的方向选择性进行比较。我们发现，兴奋性输入的差异延迟和兴奋与抑制之间的频谱偏移都与神经元的方向选择性呈正相关。因此，这两种突触机制都可能有助于听觉皮层中的 FM 方向选择性。最后，从尖峰输出测量的方向选择性明显强于基于亚阈值膜电位的方向选择性，表明选择性通过尖峰生成机制进一步增强。
