Ibbotson M R, Clifford C W, Mark R F
Developmental Neurobiology and Centre for Visual Science, Research School of Biological Sciences, Australian National University, Canberra 2601, ACT, Australia.
J Neurophysiol. 1998 Mar;79(3):1481-93. doi: 10.1152/jn.1998.79.3.1481.
Extracellular recordings of action potentials were made from directional neurons in the nucleus of the optic tract (NOT) of the wallaby, Macropus eugenii, while stimulating with moving sine-wave gratings. When a grating was moved at a constant velocity in the preferred direction through a neuron's receptive field, the firing rate increased rapidly and then declined exponentially until reaching a steady-state level. The decline in response is called motion adaptation. The rate of adaptation increased as the temporal frequency of the drifting grating increased, up to the frequency that elicited the maximum firing rate. Beyond this frequency, the adaptation rate decreased. When the adapting grating's spatial frequency was varied, such that response magnitudes were significantly different, the maximum adaptation rate occurred at similar temporal frequencies. Hence the temporal frequency of the stimulus is a major parameter controlling the rate of adaptation. In most neurons, the temporal frequency response functions measured after adaptation were shifted to the right when compared with those obtained in the unadapted state. Further insight into the adaptation process was obtained by measuring the responses of the cells to grating displacements within one frame (10.23 ms). Such impulsive stimulus movements of less than a one-quarter cycle elicited a response that rose rapidly to a maximum and then declined exponentially to the spontaneous firing rate in several seconds. The level of adaptation was demonstrated by observing how the time constants of the exponentials varied as a function of the temporal frequency of a previously presented moving grating. When plotted as functions of adapting frequency, time constants formed a U-shaped curve. The shortest time constants occurred at similar temporal frequencies, regardless of changes in spatial frequency, even when the change in spatial frequency resulted in large differences in response magnitude during the adaptation period. The strongest adaptation occurred when the adapting stimulus moved in the neuron's preferred direction. Stimuli that moved in the antipreferred direction or flickered had an adapting influence on the responses to subsequent impulsive movements, but the effect was far smaller than that elicited by preferred direction adaptation. Adaptation in one region of the receptive field did not affect the responses elicited by subsequent stimulation in nonoverlapping regions of the field. Adaptation is a significant property of NOT neurons and probably acts to expand their temporal resolving power.
在使用移动正弦波光栅刺激时，对尤金袋鼠（Macropus eugenii）视束核（NOT）中的方向神经元进行动作电位的细胞外记录。当光栅以恒定速度在神经元的感受野内沿其偏好方向移动时，放电率迅速增加，然后呈指数下降，直至达到稳态水平。这种反应下降被称为运动适应。随着漂移光栅的时间频率增加，适应率也增加，直至达到引发最大放电率的频率。超过这个频率后，适应率下降。当改变适应光栅的空间频率，使得反应幅度有显著差异时，最大适应率出现在相似的时间频率。因此，刺激的时间频率是控制适应率的主要参数。在大多数神经元中，与未适应状态下获得的时间频率响应函数相比，适应后测量的时间频率响应函数向右偏移。通过测量细胞对一帧（10.23毫秒）内光栅位移的反应，对适应过程有了进一步的了解。这种小于四分之一周期的脉冲刺激运动引发的反应迅速上升至最大值，然后在几秒钟内呈指数下降至自发放电率。通过观察指数的时间常数如何随先前呈现的移动光栅的时间频率变化来证明适应水平。当作为适应频率的函数绘制时，时间常数形成一条U形曲线。无论空间频率如何变化，最短时间常数都出现在相似的时间频率，即使空间频率的变化在适应期内导致反应幅度有很大差异。当适应刺激沿神经元的偏好方向移动时，适应最强。沿反偏好方向移动或闪烁的刺激对后续脉冲运动的反应有适应影响，但效果远小于偏好方向适应所引发的影响。感受野一个区域的适应并不影响该区域非重叠部分后续刺激所引发的反应。适应是NOT神经元的一个重要特性，可能起到扩展其时间分辨能力的作用。
