Kim Yoo Rim, Kim Chang-Eop, Yoon Heera, Kim Sun Kwang, Kim Sang Jeong
Department of Physiology, Seoul National University College of Medicine, Seoul 08826, Korea.
Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul 08826, Korea.
Exp Neurobiol. 2020 Dec 31;29(6):425-432. doi: 10.5607/en20041.
The primary somatosensory (S1) cortex plays a key role in distinguishing different sensory stimuli. Vibrotactile touch information is conveyed from the periphery to the S1 cortex through three major classes of mechanoreceptors: slowly adapting type 1 (SA1), rapidly adapting (RA), and Pacinian (PC) afferents. It has been a long-standing question whether specific populations in the S1 cortex preserve the peripheral segregation by the afferent submodalities. Here, we investigated whether S1 neurons exhibit specific responses to two distinct vibrotactile stimuli, which excite different types of mechanoreceptors (e.g., SA1 and PC afferents). Using two-photon microscopy and genetically encoded calcium indicator, GCaMP6s, we recorded calcium activities of S1 L2/3 neurons. At the same time, static (<1 Hz) and dynamic (150 Hz) vibrotactile stimuli, which are known to excite SA1 and PC, respectively, were pseudorandomly applied to the right hind paw in lightly anesthetized mice. We found that most active S1 neurons responded to both static and dynamic stimuli, but more than half of them showed preferred responses to either type of stimulus. Only a small fraction of the active neurons exhibited specific responses to either static or dynamic stimuli. However, the S1 population activity patterns by the two stimuli were markedly distinguished. These results indicate that the vibrotactile inputs driven by excitation of distinct submodalities are converged on the single cells of the S1 cortex, but are well discriminated by population activity patterns composed of neurons that have a weighted preference for each type of stimulus.
初级躯体感觉（S1）皮层在区分不同的感觉刺激中起关键作用。振动触觉信息通过三类主要的机械感受器从外周传递到S1皮层：慢适应1型（SA1）、快适应（RA）和环层小体（PC）传入纤维。S1皮层中的特定群体是否保留了由传入亚模态引起的外周分离，这一直是一个长期存在的问题。在这里，我们研究了S1神经元是否对两种不同的振动触觉刺激表现出特定反应，这两种刺激会激发不同类型的机械感受器（例如，SA1和PC传入纤维）。我们使用双光子显微镜和基因编码钙指示剂GCaMP6s记录了S1第2/3层神经元的钙活性。同时，已知分别激发SA1和PC的静态（<1 Hz）和动态（150 Hz）振动触觉刺激被伪随机施加到轻度麻醉小鼠的右后爪。我们发现，大多数活跃的S1神经元对静态和动态刺激都有反应，但其中一半以上对其中一种刺激表现出偏好反应。只有一小部分活跃神经元对静态或动态刺激表现出特定反应。然而，两种刺激引起的S1群体活动模式有明显区别。这些结果表明，由不同亚模态激发驱动的振动触觉输入汇聚在S1皮层的单个细胞上，但通过由对每种刺激类型有加权偏好的神经元组成的群体活动模式得到了很好的区分。
