Kagan Igor, Gur Moshe, Snodderly D Max
Department of Biomedical Engineering, Technion, Israel Institute of Technology, Haifa 32000, Israel.
J Neurophysiol. 2002 Nov;88(5):2557-74. doi: 10.1152/jn.00858.2001.
We studied the spatial organization of receptive fields and the responses to gratings of neurons in parafoveal V1 of alert monkeys. Activating regions (ARs) of 228 cells were mapped with increment and decrement bars while compensating for fixational eye movements. For cells with two or more ARs, the overlap between ARs responsive to increments (INC) and ARs responsive to decrements (DEC) was characterized by a quantitative overlap index (OI). The distribution of overlap indices was bimodal. The larger group (78% of cells) was composed of complex cells with strongly overlapping ARs (OI >/= 0.5). The smaller group (14%) was composed of simple cells with minimal spatial overlap of ARs (OI </= 0.3). Simple cells were preferentially located in layers dominated by the magnocellular pathway. A third group of neurons, the monocontrast cells (8%), responded only to one sign of contrast and had more sustained responses to flashed stimuli than other cells. One hundred fourteen neurons were also studied with drifting sinusoidal gratings of various spatial frequencies and window widths. For complex cells, the relative modulation (RM, the ratio of the 1st harmonic to the mean firing rate), ranged from 0.6 +/- 0.4 to 1.1 +/- 0.5 (mean +/- SD), depending on the stimulus conditions and the mode of correction for eye movements. RM was not correlated with the degree of overlap of ARs, indicating that the spatial organization of receptive fields cannot reliably be predicted from RM values. In fact, a subset of complex cells had RM > 1, the traditional criterion for identifying simple cells. However, unlike simple cells, even those complex cells with high RM could exhibit diverse nonlinear responses when the spatial frequency or window size was changed. Furthermore, the responses of complex cells to counterphase gratings were predominantly nonlinear even harmonics. These results show that RM is not a robust test of linearity. Our results indicate that complex cells are the most frequently encountered neurons in primate V1, and their behavior needs to receive more emphasis in models of visual function.
我们研究了警觉猴子副中央凹V1区感受野的空间组织以及神经元对光栅的反应。在补偿注视性眼动的同时，用递增和递减条对228个细胞的激活区域（ARs）进行映射。对于具有两个或更多ARs的细胞，对递增（INC）反应的ARs与对递减（DEC）反应的ARs之间的重叠通过定量重叠指数（OI）来表征。重叠指数的分布是双峰的。较大的一组（占细胞的78%）由具有强烈重叠ARs的复杂细胞组成（OI≥0.5）。较小的一组（14%）由ARs空间重叠最小的简单细胞组成（OI≤0.3）。简单细胞优先位于由大细胞通路主导的层中。第三组神经元，即单对比度细胞（8%），仅对一种对比度信号有反应，并且对闪光刺激的反应比其他细胞更持久。还使用各种空间频率和窗口宽度的漂移正弦光栅对114个神经元进行了研究。对于复杂细胞，相对调制（RM，基波与平均放电率的比值）范围从0.6±0.4到1.1±0.5（平均值±标准差），这取决于刺激条件和眼动校正模式。RM与ARs的重叠程度无关，表明不能从RM值可靠地预测感受野的空间组织。事实上，一部分复杂细胞的RM>1，这是识别简单细胞的传统标准。然而，与简单细胞不同，即使是那些RM值高的复杂细胞，当空间频率或窗口大小改变时，也可能表现出多样的非线性反应。此外，复杂细胞对反相光栅的反应主要是非线性偶次谐波。这些结果表明RM不是线性的可靠测试。我们的结果表明，复杂细胞是灵长类动物V1区最常见的神经元，它们的行为在视觉功能模型中需要得到更多的重视。
