SENSITIVITY OF MST NEURONS TO OPTIC FLOW STIMULI .2. MECHANISMS OF RESPONSE SELECTIVITY REVEALED BY SMALL-FIELD STIMULI
SENSITIVITY OF MST NEURONS TO OPTIC FLOW STIMULI .2. MECHANISMS OF RESPONSE SELECTIVITY REVEALED BY SMALL-FIELD STIMULI
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DOI：
10.1152/jn.1991.65.6.1346
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发表时间：
1991-06-01
影响因子：
2.5
通讯作者：
WURTZ, RH
中科院分区：
文献类型：
--
作者：
DUFFY, CJ;WURTZ, RH
1. 在这些实验中，我们研究的感受野机制，支持光流场选择性反应的神经元的背内侧区的内侧上级颞区（MSTd）。 我们的实验测试了光流场选择性的两个假设的预测。 方向镶嵌假说指出，这些感受野包含一组平面方向选择性子场，匹配光流场内的局部运动方向。 矢量场假说指出，这些感受野是唯一敏感的平面，圆形或径向光流场的分布特性。 使用大视野刺激的实验表明，一些神经元显示视流场选择性的变化取决于刺激在感受野中的位置;这些是位置依赖性反应。 然而，其他神经元保持相同的光流场的选择性，尽管刺激位置的变化，这些是位置不变的反应。 我们已经使用的光流场选择性的位置依赖性或不变性作为一种方式来测试的方向马赛克和矢量场的假设。 位置相关性更符合方向镶嵌假设，而位置不变性更符合向量场假设. 为了测试位置效应，我们研究了160个MSTd神经元的大感受野内的小子域的光流场选择性。 首先，我们将不同大小的小视野光流刺激集中在感受野的同一位置。 大多数MSTd神经元的反应幅度随刺激大小的减小而减小，但维持了光流场的选择性. 然后，我们在这些MSTd神经元的大感受野内的不同位置放置小野刺激。 位置不变的反应选择性是最突出的单成分神经元，这表明他们更符合向量场假说。 位置依赖性反应选择性在三成分神经元中最为突出，这表明它们更符合方向镶嵌假说。 然而，这些三成分神经元感受野的平面方向偏好性的变化与大视野圆形或径向选择性的方向镶嵌解释不一致. 小视野位置的研究也表明存在的区域内的感受野中，无论是方向选择性抑制或方向选择性兴奋反应占主导地位。 这些区域之间的重叠程度从非选择性增加到三重-双重-最后到单组分神经元。 我们认为，这些神经元的感受野内的兴奋和抑制梯度的重叠可能有助于解释它们对复杂刺激的反应。 我们的假设依赖于兴奋性和抑制性平面反应梯度的相对强度、重叠、方向和位置的定量变化。 这些参数的变化可能占连续的响应类型，而不是离散的类别，表征MSTd神经元的响应光流场刺激。
1. In these experiments we examined the receptive field mechanisms that support the optic flow field selective responses of neurons in the dorsomedial region of the medial superior temporal area (MSTd). Our experiments tested the predictions of two hypotheses of optic flow field selectivity. The direction mosaic hypothesis states that these receptive fields contain a set of planar direction-selective subfields that match the local directions of motion within optic flow fields. The vector field hypothesis states that these receptive fields are uniquely sensitive to distributed properties of planar, circular, or radial optic flow fields.2. Experiments using large-field stimuli revealed that some neurons showed changes in optic flow field selectivity depending on the position of the stimulus in the receptive field; these are position-dependent responses. However, other neurons maintained the same optic flow field selectivities in spite of changes in stimulus position; these are position-invariant responses. We have used the position dependence or invariance of optic flow field selectivity as a way of testing the direction mosaic and vector field hypotheses. Position dependence is more consistent with the direction mosaic hypothesis, whereas position invariance is more consistent with the vector field hypothesis.3. To test for position effects, we examined the optic flow field selectivity of small subfields within the large receptive fields of 160 MSTd neurons. First, we centered small-field optic flow stimuli of various sizes over the same position in the receptive field. Most MSTd neurons showed decreasing response amplitude with decreasing stimulus size but maintained optic flow field selectivity.4. We then placed small-field stimuli at various positions within the large receptive field of these MSTd neurons. Position-invariant response selectivity was most prominent in single-component neurons, suggesting that they were more consistent with the vector field hypothesis. Position-dependent response selectivity was most prominent in triple-component neurons, suggesting that they were more consistent with the direction mosaic hypothesis. However, the variations in planar direction preference throughout the receptive field of these triple-component neurons were not consistent with a direction mosaic explanation of the large-field circular or radial selectivity observed.5. Small-field position studies also demonstrated the existence of zones within the receptive field in which either direction-selective inhibitory or direction-selective excitatory responses predominated. The degree of overlap between these zones increased from nonselective to triple- to double- and finally to single-component neurons.6. We suggest that the overlap of gradients of excitation and inhibition within the receptive field of these neurons might help to explain their responses to complex stimuli. Our hypothesis relies on quantitative variations in the relative strength, overlap, directions, and positions of excitatory and inhibitory planar response gradients. Changes in these parameters might account for the continuum of response types rather than discrete categories that characterize the responses of MSTd neurons to optic flow field stimuli.