Mikami A
Department of Neurophysiology, Kyoto University, Inuyama, Japan.
Exp Brain Res. 1992;90(1):40-6. doi: 10.1007/BF00229254.
In an attempt to elucidate the mechanisms of directional selectivity in the neurons of the middle temporal visual area (MT) of macaque monkeys, we presented small numbers of sequentially flashed stimuli with various temporal and spatial intervals within the receptive field (RF) of direction-selective MT neurons. Experiments were performed using awake macaque monkeys trained to fixate on a set of short stationary lines. Stimuli were presented on a CRT screen under computer control. In two-flash experiments, responses to a test flash presented in the center of the RF were examined following a conditioning flash presented in various locations within the RF. Inhibition in the null direction was observed in about 78% of MT neurons, while facilitation was relatively weak in this group of neurons. In most of these neurons, the ranges of temporal and spatial intervals that produced directional selectivity in two-flash experiments were within half the values and double the values, respectively of those in multi-flash experiments. In the remaining 22% of direction-selective MT neurons, several flashed stimuli were necessary to produce directional selectivity. Most of these neurons showed facilitation in the preferred direction. It appears that the inhibitory mechanisms in the null direction are sufficiently strong to be induced by a single conditioning flash whereas the facilitatory mechanisms are weaker and several stimuli are required for production of the direction-selective response.
为了阐明猕猴颞中视觉区（MT）神经元方向选择性的机制，我们在方向选择性MT神经元的感受野（RF）内，以不同的时间和空间间隔呈现少量顺序闪烁的刺激。实验使用经过训练能注视一组短固定线条的清醒猕猴进行。刺激在计算机控制下呈现在阴极射线管屏幕上。在双闪实验中，在RF内不同位置呈现条件闪光后，检测对呈现在RF中心的测试闪光的反应。在约78%的MT神经元中观察到无效方向的抑制，而在这组神经元中促进作用相对较弱。在大多数这些神经元中，双闪实验中产生方向选择性的时间和空间间隔范围分别在多闪实验的一半值和两倍值之内。在其余22%的方向选择性MT神经元中，需要几个闪烁刺激才能产生方向选择性。这些神经元中的大多数在偏好方向上表现出促进作用。似乎无效方向的抑制机制足够强大，可由单个条件闪光诱导，而促进机制较弱，产生方向选择性反应需要几个刺激。
