Manzoni D, Andre P, Pompeiano O
Dipartimento di Fisiologia e Biochimica, Università di Pisa, Italy.
Pflugers Arch. 1995 Dec;431(2):141-54. doi: 10.1007/BF00410185.
Responses of 67 Purkinje cells (P-cells) and 44 unidentified neurons (U-cells) located in the cerebellar anterior vermis were recorded in decerebrate cats during off-vertical axis rotation (OVAR). This stimulus consisted of a slow constant velocity (9.4%/s) rotation in the clockwise (CW) and counterclockwise (CCW) directions around an axis inclined by 5 degrees with respect to the vertical. OVAR imposes on the animal head a 5 degrees tilt, whose direction changes continuously over the horizontal plane, thus eliciting a selective stimulation of macular receptors. A total of 27/67 P-cells (40%) and 24/44 U-cells (55%) responded to both CW and CCW rotations. For these bidirectional units, the direction of maximum sensitivity to tilt (Smax) could be identified. Smax directions were distributed over the whole horizontal plane of stimulation. Among bidirectional neurons, 48% of the P-cells and 33% of the U-cells displayed an equal amplitude of modulation during CW and CCW rotations, indicating a cosine-tuned behaviour. In these instances, the temporal phase of the unit response to a given direction of tilt remained constant, while the sensitivity was maximal along the Smax direction and declined with the cosine of the angle between Smax and the tilt direction. The remaining bidirectional units displayed unequal amplitudes of modulation during CW and CCW rotations. For these neurons, a nonzero sensitivity along the null direction was expected and the response phase varied as a function of stimulus direction. Finally, 31% and 23% of P-cells and U-cells, respectively, responded during OVAR in one direction only (unidirectional units). This behaviour predicts equal sensitivities along any tilt direction in the horizontal plane and a response phase that changes linearly with the stimulus direction. The posibility that the tested neurons formed a population which coded the direction of head tilt in space was also investigated. The data from the whole population of cells were analysed using a modified version of vectorial analysis. This model assumes that for a particular tilt each cell makes vectorial contributions; the vectorial sum of these contributions represent the outcome of the population code and points in the direction of head tilt in space. Thus, a dynamic head tilt along four representative directions was simulated. For each of the four directions, 12 population vectors were calculated at regular time intervals so as to cover an entire cycle of head tilt. The results indicate that for each selected time in the cycle the direction of the population vector closely corresponded to that of the head tilt, while its amplitude was related to the amount of head tilt. These data were particularly obtained for the P-cells. In view of their efferent connections, the cerebellar anterior vermis may provide a framework for the spatial organization of vestibulospinal reflexes induced by stimulation of otolith receptors.
在去大脑猫处于非垂直轴旋转（OVAR）期间，记录了位于小脑前蚓部的67个浦肯野细胞（P细胞）和44个未识别神经元（U细胞）的反应。该刺激包括以9.4%/秒的恒定速度在顺时针（CW）和逆时针（CCW）方向围绕相对于垂直轴倾斜5度的轴进行缓慢旋转。OVAR使动物头部产生5度的倾斜，其方向在水平面上不断变化，从而引发黄斑感受器的选择性刺激。总共27/67个P细胞（40%）和24/44个U细胞（55%）对CW和CCW旋转均有反应。对于这些双向单位，可以确定对倾斜的最大敏感度方向（Smax）。Smax方向分布在整个刺激水平面上。在双向神经元中，48%的P细胞和33%的U细胞在CW和CCW旋转期间表现出相等的调制幅度，表明具有余弦调谐行为。在这些情况下，单位对给定倾斜方向的反应的时间相位保持恒定，而敏感度在Smax方向上最大，并随着Smax与倾斜方向之间角度的余弦而下降。其余双向单位在CW和CCW旋转期间表现出不相等的调制幅度。对于这些神经元，预计在零方向上有非零敏感度，并且反应相位随刺激方向而变化。最后，分别有31%的P细胞和23%的U细胞仅在OVAR的一个方向上有反应（单向单位）。这种行为预测在水平面上沿任何倾斜方向具有相等的敏感度，并且反应相位随刺激方向线性变化。还研究了所测试的神经元是否形成了一个编码空间中头部倾斜方向的群体的可能性。使用矢量分析的修改版本对整个细胞群体的数据进行了分析。该模型假设对于特定的倾斜，每个细胞做出矢量贡献；这些贡献的矢量和代表群体编码的结果，并指向空间中头部倾斜的方向。因此，模拟了沿四个代表性方向的动态头部倾斜。对于这四个方向中的每一个，以规则的时间间隔计算12个群体矢量，以覆盖头部倾斜的整个周期。结果表明，在周期中的每个选定时间，群体矢量的方向与头部倾斜的方向密切对应，而其幅度与头部倾斜的量有关。这些数据尤其在P细胞中获得。鉴于它们的传出连接，小脑前蚓部可能为耳石感受器刺激诱导的前庭脊髓反射的空间组织提供一个框架。
