Data from: Neurons in primate visual cortex alternate between responses to multiple stimuli in their receptive field

A fundamental question concerning representation of the visual world in our brain is how a cortical cell responds when presented with more than a single stimulus. We find supportive evidence that most cells presented with a pair of stimuli respond predominantly to one stimulus at a time, rather than a weighted average response. Traditionally, the firing rate is assumed to be a weighted average of the firing rates to the individual stimuli (response-averaging model) (Bundesen et al., 2005). Here, we also evaluate a probability-mixing model (Bundesen et al., 2005), where neurons temporally multiplex the responses to the individual stimuli. This provides a mechanism by which the representational identity of multiple stimuli in complex visual scenes can be maintained despite the large receptive fields in higher extrastriate visual cortex in primates. We compare the two models through analysis of data from single cells in the middle temporal visual area (MT) of rhesus monkeys when presented with two separate stimuli inside their receptive field with attention directed to one of the two stimuli or outside the receptive field. The spike trains were modeled by stochastic point processes, including memory effects of past spikes and attentional effects, and statistical model selection between the two models was performed by information theoretic measures as well as the predictive accuracy of the models. As an auxiliary measure, we also tested for uni- or multimodality in interspike interval distributions, and performed a correlation analysis of simultaneously recorded pairs of neurons, to evaluate population behavior.关于大脑中视觉世界表征的核心问题之一是：当单个皮层细胞受到多个刺激时，其响应模式是怎样的。本研究获得支持性证据：多数接受成对刺激的皮层细胞会在同一时刻优先响应其中一个刺激，而非对两种刺激的响应进行加权平均。传统研究中，神经元的放电率被假定为单个刺激对应的放电率的加权平均值（响应平均模型，response-averaging model）（Bundesen等，2005）。本研究同时评估了概率混合模型（probability-mixing model，Bundesen等，2005），该模型提出神经元会在时序上复用对单个刺激的响应。该模型为灵长类动物纹外视觉皮层高级区域内具有大感受野的场景下，维持复杂视觉场景中多个刺激的表征同一性提供了一种可行机制。本研究通过分析恒河猴颞中视觉区（middle temporal visual area, MT）的单个神经元实验数据，对两种模型进行对比：实验过程中，向神经元的感受野（receptive field）内同时呈现两个独立刺激，并将其注意力引导至两个刺激中的一个或感受野以外的区域。本研究采用随机点过程对锋电位序列（spike trains）进行建模，其中纳入了既往锋电位的记忆效应与注意力调控效应；随后通过信息论指标与模型预测精度，完成两种模型间的统计模型选择。作为辅助分析手段，本研究还对锋电位间期（interspike interval）的分布开展单峰或多峰性检验，并对同时记录的神经元对进行相关性分析，以评估群体神经元的行为特性。