Department of Biology, University of Maryland , College Park, MD 20742.
Center for Biomedical Engineering and Technology, and Department of Physiology, University of Maryland School of Medicine , Baltimore, MD 21201.
eNeuro. 2017 Apr 6;4(2). doi: 10.1523/ENEURO.0092-17.2017. eCollection 2017 Mar-Apr.
Sensory cortices do not work in isolation. The functional responses of neurons in primary sensory cortices can be affected by activity from other modalities. For example, short-term visual deprivations, or dark exposure (DE), leads to enhanced neuronal responses and frequency selectivity to sounds in layer 4 (L4) of primary auditory cortex (A1). Circuit changes within A1 likely underlie these changes. Prior studies revealed that DE enhanced thalamocortical transmission to L4 in A1. Because the frequency selectivity of L4 neurons is determined by both thalamocortical and intracortical inputs, changes in intralaminar circuits to L4 neurons might also contribute to improved sound responses. We thus investigated in mouse A1 whether intracortical circuits to L4 cells changed after DE. Using in vitro whole-cell patch recordings in thalamocortical slices from mouse auditory cortex, we show that DE can lead to refinement of interlaminar excitatory as well as inhibitory connections from L2/3 to L4 cells, manifested as a weakening of these connections. The circuit refinement is present along the tonotopic axis, indicating reduced integration along the tonotopic axis. Thus, cross-modal influences may alter the spectral and temporal processing of sensory stimuli in multiple cortical layers by refinement of thalamocortical and intracortical circuits.
感觉皮层并非孤立运作。初级感觉皮层中的神经元的功能反应会受到来自其他感觉模态的活动的影响。例如，短期的视觉剥夺或暗适应（DE）会导致初级听觉皮层（A1）的第 4 层（L4）神经元对声音的反应增强和频率选择性提高。A1 内的回路变化可能是这些变化的基础。先前的研究表明，DE 增强了 A1 中 L4 的丘脑皮质传递。由于 L4 神经元的频率选择性取决于丘脑皮质和皮质内的输入，因此 L4 神经元的内层回路的变化也可能有助于改善声音反应。因此，我们在小鼠 A1 中研究了 DE 后 L4 细胞的皮质内回路是否发生了变化。使用来自小鼠听觉皮层的丘脑皮质切片中的体外全细胞膜片钳记录，我们表明 DE 可以导致 L2/3 到 L4 细胞的层间兴奋性和抑制性连接的细化，表现为这些连接的减弱。这种回路细化沿音调轴存在，表明音调轴上的整合减少。因此，跨模态影响可能通过丘脑皮质和皮质内回路的细化来改变多个皮质层中感觉刺激的光谱和时间处理。
