Lozano Yave Roberto, Page Hector, Jacob Pierre-Yves, Lomi Eleonora, Street James, Jeffery Kate
Division of Psychology and Language Sciences, University College London, London, UK.
Brain Neurosci Adv. 2017 Sep 15;1:2398212817721859. doi: 10.1177/2398212817721859. eCollection 2017.
Visual landmarks are used by head direction (HD) cells to establish and help update the animal's representation of head direction, for use in orientation and navigation. Two cortical regions that are connected to primary visual areas, postsubiculum (PoS) and retrosplenial cortex (RSC), possess HD cells: we investigated whether they differ in how they process visual landmarks.
We compared PoS and RSC HD cell activity from tetrode-implanted rats exploring an arena in which correct HD orientation required discrimination of two opposing landmarks having high, moderate or low discriminability.
RSC HD cells had higher firing rates than PoS HD cells and slightly lower modulation by angular head velocity, and anticipated actual head direction by ~48 ms, indicating that RSC spiking leads PoS spiking. Otherwise, we saw no differences in landmark processing, in that HD cells in both regions showed equal responsiveness to and discrimination of the cues, with cells in both regions having unipolar directional tuning curves and showing better discrimination of the highly discriminable cues. There was a small spatial component to the signal in some cells, consistent with their role in interacting with the place cell navigation system, and there was also slight modulation by running speed. Neither region showed theta modulation of HD cell spiking.
That the cells can immediately respond to subtle differences in spatial landmarks is consistent with rapid processing of visual snapshots or scenes; similarities in PoS and RSC responding may be due either to similar computations being performed on the visual inputs, or to rapid sharing of information between these regions. More generally, this two-cue HD cell paradigm may be a useful method for testing rapid spontaneous visual discrimination capabilities in other experimental settings.
头部方向（HD）细胞利用视觉地标来建立并帮助更新动物的头部方向表征，以用于定向和导航。与初级视觉区域相连的两个皮质区域，即后下托（PoS）和压后皮质（RSC），拥有HD细胞：我们研究了它们在处理视觉地标方面是否存在差异。
我们比较了来自植入四极管的大鼠的PoS和RSC HD细胞活动，这些大鼠在一个实验场地中探索，在该场地中，正确的HD定向需要区分两个具有高、中或低可辨别性的相对地标。
RSC HD细胞的放电频率高于PoS HD细胞，并且受头部角向速度的调制略低，并且比实际头部方向提前约48毫秒，这表明RSC的尖峰活动领先于PoS的尖峰活动。否则，我们在地标处理方面未发现差异，因为两个区域的HD细胞对线索的反应和辨别能力相同，两个区域的细胞都具有单极方向调谐曲线，并且对高可辨别性线索的辨别能力更好。一些细胞的信号存在小的空间成分，这与其在与位置细胞导航系统相互作用中的作用一致，并且也受奔跑速度的轻微调制。两个区域均未显示HD细胞尖峰活动的θ调制。
细胞能够立即对空间地标的细微差异做出反应，这与视觉快照或场景的快速处理一致；PoS和RSC反应的相似性可能是由于对视觉输入执行了相似的计算，或者是由于这些区域之间信息的快速共享。更一般地说，这种双线索HD细胞范式可能是在其他实验环境中测试快速自发视觉辨别能力的有用方法。
