CAREER: Neural Representations Based on Temporal Structure: A Computational Neuroscience Approach

摘要外部世界是如何在大脑中表现出来的？在最低层次上，我们知道大脑的基本计算单位是神经细胞或神经元。我们还知道，神经元利用被称为“动作电位”的电脉冲相互交流。我们不知道的是这些脉冲是如何编码信息的，例如，生物体环境的表征。一个常见的观点是，感知对象的属性被编码为神经元的平均放电率（“速率代码”），但这不仅是一个低效的过程，而且当大脑必须同时处理多个对象时，它也会产生问题，这是通常的情况。其中一个问题是，如果某个属性是由相应的峰值速率编码的，并且如果几个对象都具有该属性，那么如何决定该属性属于这些对象中的哪个？大脑不仅仅是绘制外部世界；有机体的行为也取决于它的内部状态。大脑必须解决的问题之一是信息过载，这是由于大量的刺激时刻冲击着传感器造成的。因此，大脑最重要的功能之一就是仔细选择那些重要的刺激，并只考虑这些细节。例如，当你在阅读这篇文章时，你的注意力集中在文字上，你可能没有考虑到你的左脚穿左鞋的感觉。然而，既然你试着去“感受”它，你就可以“关注”它。我们知道，无论你是否注意，你脚上的触觉传感器的行为都是一样的，但对大脑来说，这两种情况显然是不同的。当你把注意力从一种刺激转移到另一种刺激时，大脑的活动究竟发生了什么变化？理论模型预测，大脑使用的代码不仅使用平均速率，而且还使用动作脉冲序列的更细粒度的时间结构。例如，据预测，集中注意力不一定会改变平均放电率，但不同神经元之间的放电关系，例如，使神经元更有可能一起放电。尼伯博士和他的学生们将比较猴子在执行一项需要它们注意刺激的任务时的神经元活动，以及它们在接受同样的刺激但不注意时的神经元活动。初步结果以及数学模型表明，在神经元的相对放电中确实存在这样的差异。除了分析猴子完成任务时的神经活动外，他们还将开发注意力处理的数学模型。

Niebur9876721AbstractHow is the external world represented in the brain? At the lowest level, we know that the basic computational units of the brain are nerve cells, or neurons. We also know that neurons use electrical impulses called "action potentials" to communicate with each other. What we do not know is how these impulses code information, for instance, the representation of the organism's environment. A common view is that properties of perceived objects are coded as the average firing rates of neurons ("rate code") but this is not only an inefficient procedure, it also creates problems when the brain has to deal with more than one object simultaneously, as is usually the case. One of the problems is that, if a certain property is coded by a corresponding spike rate, and if several objects have this property, how does one decide to which of those objects the property belongs?The brain does more than just map out the external world; the behavior of an organism also depends on its internal states. One of the problems the brain has to solve is information overload, resulting from the multitude of stimuli impinging on the sensors at all times. Therefore, one of the brain's most important functions is to carefully select those stimuli that are important, and to consider only these in detail. For instance, while you are reading this text, you are focusing on the written words and you are probably not thinking about how your left foot feels in your left shoe. However, now that you try to "feel" it, you can "pay attention" to it. We know that the tactile sensors in your foot behave the same way whether you are paying attention to it or not, but for the brain the two situations are clearly different. What, precisely, changes in the activity of the brain when you direct your attention from one stimulus to another?Theoretical models have predicted that the code used by the brain not only uses the average rate but also more fine-grained temporal structures of the sequences of action impulses. For instance, it has been predicted that paying attention does not necessarily change the average firing rate, but the relations between the firing in different neurons, for instance, make it more likely that neurons fire together. Dr. Niebur and his students will compare the activity of neurons in monkeys performing a task that requires them to attend to a stimulus with the activity when they receive the same stimulation but are NOT attending to it. Preliminary results, as well as mathematical modeling, have indicated that there is indeed, such a difference in the relative firing of neurons. In addition to analyzing the neural activity of the monkey working on the task, they will also develop mathematical models of attentional processing.