Department of Biomedical Engineering, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA.
J Neurosci. 2012 Mar 7;32(10):3499-515. doi: 10.1523/JNEUROSCI.3585-11.2012.
Human cognition is characterized by flexibility, the ability to select not only which action but which cognitive process to engage to best achieve the current behavioral objective. The ability to tailor information processing in the brain to rules, goals, or context is typically referred to as executive control, and although there is consensus that prefrontal cortex is importantly involved, at present we have an incomplete understanding of how computational flexibility is implemented at the level of prefrontal neurons and networks. To better understand the neural mechanisms of computational flexibility, we simultaneously recorded the electrical activity of groups of single neurons within prefrontal and posterior parietal cortex of monkeys performing a task that required executive control of spatial cognitive processing. In this task, monkeys applied different spatial categorization rules to reassign the same set of visual stimuli to alternative categories on a trial-by-trial basis. We found that single neurons were activated to represent spatially defined categories in a manner that was rule dependent, providing a physiological signature of a cognitive process that was implemented under executive control. We found also that neural signals coding rule-dependent categories were distributed between the parietal and prefrontal cortex--however, not equally. Rule-dependent category signals were stronger, more powerfully modulated by the rule, and earlier to emerge in prefrontal cortex relative to parietal cortex. This suggests that prefrontal cortex may initiate the switch in neural representation at a network level that is important for computational flexibility.
人类认知的特点是灵活性，能够选择不仅要采取哪种行动，还要选择哪种认知过程来最好地实现当前的行为目标。根据规则、目标或上下文调整信息处理的能力通常被称为执行控制，尽管人们普遍认为前额叶皮层很重要，但目前我们对前额叶神经元和网络如何实现计算灵活性的理解还不完整。为了更好地理解计算灵活性的神经机制，我们同时记录了猴子执行需要执行控制空间认知处理的任务时前额叶和顶叶后皮质中一群单个神经元的电活动。在这项任务中，猴子根据不同的空间分类规则，将相同的视觉刺激集在逐次基础上重新分配到不同的类别。我们发现，单个神经元以依赖规则的方式被激活，以代表空间定义的类别，为在执行控制下实施的认知过程提供了生理特征。我们还发现，编码依赖规则的类别的神经信号在顶叶和前额叶皮质之间分布——然而，并非平均分布。相对于顶叶皮质，前额叶皮质中与规则相关的类别信号更强、受规则的调制更强、出现得更早。这表明，前额叶皮层可能会在网络层面上启动神经表示的转换，这对于计算灵活性很重要。
