Bayguinov Peter O, Ghitani Nima, Jackson Meyer B, Basso Michele A
Department of Neuroscience, University of Wisconsin, Madison, Wisconsin;
Department of Neuroscience, University of Wisconsin, Madison, Wisconsin; Neuroscience Training Program, University of Wisconsin, Madison, Wisconsin;
J Neurophysiol. 2015 Jul;114(1):662-76. doi: 10.1152/jn.00144.2015. Epub 2015 May 20.
The mammalian superior colliculus (SC) is a laminar midbrain structure that translates visual signals into commands to shift the focus of attention and gaze. The SC plays an integral role in selecting targets and ultimately generating rapid eye movements to those targets. In all mammals studied to date, neurons in the SC are arranged topographically such that the location of visual stimuli and the endpoints of orienting movements form organized maps in superficial and deeper layers, respectively. The organization of these maps is thought to underlie attentional priority by assessing which regions of the visual field contain behaviorally relevant information. Using voltage imaging and patch-clamp recordings in parasagittal SC slices from the rat, we found the synaptic circuitry of the visuosensory map in the SC imposes a strong bias. Voltage imaging of responses to electrical stimulation revealed more spread in the caudal direction than the rostral direction. Pharmacological experiments demonstrated that this asymmetry arises from GABAA receptor activation rostral to the site of stimulation. Patch-clamp recordings confirmed this rostrally directed inhibitory circuit and showed that it is contained within the visuosensory layers of the SC. Stimulation of two sites showed that initial stimulation of a caudal site can take priority over subsequent stimulation of a rostral site. Taken together, our data indicate that the circuitry of the visuosensory SC is hard-wired to give higher priority to more peripheral targets, and this property is conferred by a uniquely structured, dedicated inhibitory circuit.
哺乳动物的上丘（SC）是一种分层的中脑结构，它将视觉信号转化为指令，以转移注意力和注视焦点。上丘在选择目标并最终向这些目标产生快速眼动方面起着不可或缺的作用。在迄今为止研究的所有哺乳动物中，上丘中的神经元按拓扑结构排列，使得视觉刺激的位置和定向运动的终点分别在浅层和深层形成有组织的图谱。这些图谱的组织被认为通过评估视野的哪些区域包含行为相关信息来构成注意力优先级的基础。利用大鼠矢状旁切片中的电压成像和膜片钳记录，我们发现上丘中视觉感觉图谱的突触回路存在强烈的偏向性。对电刺激反应的电压成像显示，尾侧方向的扩散比头侧方向更大。药理学实验表明，这种不对称性源于刺激部位头侧的GABAA受体激活。膜片钳记录证实了这种头侧定向的抑制性回路，并表明它包含在上丘的视觉感觉层内。对两个部位的刺激表明，最初对尾侧部位的刺激可以优先于随后对头侧部位的刺激。综上所述，我们的数据表明，视觉感觉上丘的回路被硬性连接，以便赋予更外周的目标更高的优先级，并且这种特性是由一个结构独特、专门的抑制性回路赋予的。
