Blair H T, Lipscomb B W, Sharp P E
Department of Psychology, Yale University, New Haven, Connecticut 06520-8205, USA.
J Neurophysiol. 1997 Jul;78(1):145-59. doi: 10.1152/jn.1997.78.1.145.
Head-direction cells are neurons that signal a rat's directional heading in the horizontal plane. Head-direction cells in the anterior thalamus are anticipatory, so that their firing rate is better correlated with the rat's future head direction than with the present or past head direction. We recorded single-unit activity from head-direction cells in the anterior thalamus of freely moving rats. We measured the time interval by which each individual cell anticipated the rat's future head direction, which we refer to as the cell's anticipatory time interval (ATI). Head-direction cells in the anterior thalamus anticipated the rat's future head direction by an average ATI of approximately 17 ms. However, different anterior thalamic cells consistently anticipated the future head direction by different ATIs ranging between 0 and 50 ms. We found that the ATI of an anterior thalamic head-direction cell was correlated with several parameters of the cell's directional tuning function. First, cells with long ATIs sometimes appeared to have two peaks in their directional tuning function, whereas cells with short ATIs always had only one peak. Second, the ATI of a cell was negatively correlated with the cell's peak firing rate, so that cells with longer ATIs fired at a slower rate than cells with shorter ATIs. Third, a cell's ATI was correlated with the width of its directional tuning function, so that cells with longer ATIs had broader tuning widths than cells with shorter ATIs. These relationships between a cell's ATI and its directional tuning parameters could not be accounted for by artifactual broadening of the tuning function, which occurs for cells that fire in correlation with the future (rather than present) head direction. We found that when the rat's head is turning, the shape of an anterior thalamic head-direction cell's tuning function changes in a systematic way, becoming taller, narrower, and skewed. This systematic change in the shape of the tuning function may be what causes anterior thalamic cells to effectively anticipate the rat's future head direction. We propose a neural circuit mechanism to account for the firing behavior we have observed in our experiments, and we discuss how this circuit might serve as a functional component of a neural system for path integration of the rat's directional heading.
头部方向细胞是在水平面内指示大鼠方向朝向的神经元。丘脑前核中的头部方向细胞具有前瞻性，因此它们的放电频率与大鼠未来的头部方向比与当前或过去的头部方向具有更好的相关性。我们记录了自由活动大鼠丘脑前核中头部方向细胞的单单位活动。我们测量了每个细胞预测大鼠未来头部方向的时间间隔，我们将其称为细胞的预测时间间隔（ATI）。丘脑前核中的头部方向细胞预测大鼠未来头部方向的平均ATI约为17毫秒。然而，不同的丘脑前核细胞始终以0至50毫秒之间的不同ATI预测未来头部方向。我们发现丘脑前核头部方向细胞的ATI与该细胞方向调谐函数的几个参数相关。首先，具有长ATI的细胞在其方向调谐函数中有时似乎有两个峰值，而具有短ATI的细胞总是只有一个峰值。其次，细胞的ATI与其峰值放电频率呈负相关，因此具有较长ATI的细胞放电速率比具有较短ATI的细胞慢。第三，细胞的ATI与其方向调谐函数的宽度相关，因此具有较长ATI的细胞比具有较短ATI的细胞具有更宽的调谐宽度。细胞的ATI与其方向调谐参数之间的这些关系不能通过调谐函数的人为展宽来解释，这种展宽发生在与未来（而非当前）头部方向相关放电的细胞中。我们发现，当大鼠头部转动时，丘脑前核头部方向细胞调谐函数的形状会以一种系统的方式发生变化，变得更高、更窄且有偏斜。调谐函数形状的这种系统变化可能是导致丘脑前核细胞有效预测大鼠未来头部方向的原因。我们提出了一种神经回路机制来解释我们在实验中观察到的放电行为，并讨论了该回路如何作为大鼠方向朝向路径整合神经系统的功能组件。
