Asaad Wael F, Lauro Peter M, Perge János A, Eskandar Emad N
Department of Neurosurgery and
Department of Neuroscience, Brown University, Providence, Rhode Island 02912.
J Neurosci. 2017 Jul 19;37(29):6995-7007. doi: 10.1523/JNEUROSCI.3311-16.2017. Epub 2017 Jun 20.
To adapt successfully to our environments, we must use the outcomes of our choices to guide future behavior. Critically, we must be able to correctly assign credit for any particular outcome to the causal features which preceded it. In some cases, the causal features may be immediately evident, whereas in others they may be separated in time or intermingled with irrelevant environmental stimuli, creating a potentially nontrivial credit-assignment problem. We examined the neuronal representation of information relevant for credit assignment in the dorsolateral prefrontal cortex (dlPFC) of two male rhesus macaques performing a task that elicited key aspects of this problem. We found that neurons conveyed the information necessary for credit assignment. Specifically, neuronal activity reflected both the relevant cues and outcomes at the time of feedback and did so in a manner that was stable over time, in contrast to prior reports of representational instability in the dlPFC. Furthermore, these representations were most stable early in learning, when credit assignment was most needed. When the same features were not needed for credit assignment, these neuronal representations were much weaker or absent. These results demonstrate that the activity of dlPFC neurons conforms to the basic requirements of a system that performs credit assignment, and that spiking activity can serve as a stable mechanism that links causes and effects. Credit assignment is the process by which we infer the causes of our successes and failures. We found that neuronal activity in the dorsolateral prefrontal cortex conveyed the necessary information for performing credit assignment. Importantly, while there are various potential mechanisms to retain a "trace" of the causal events over time, we observed that spiking activity was sufficiently stable to act as the link between causes and effects, in contrast to prior reports that suggested spiking representations were unstable over time. In addition, we observed that this stability varied as a function of learning, such that the neural code was more reliable over time during early learning, when it was most needed.
为了成功适应我们的环境，我们必须利用选择的结果来指导未来的行为。至关重要的是，我们必须能够将任何特定结果的功劳正确地归因于其之前的因果特征。在某些情况下，因果特征可能显而易见，而在其他情况下，它们可能在时间上相隔甚远，或者与无关的环境刺激交织在一起，从而产生一个潜在的重要的功劳分配问题。我们研究了两只雄性恒河猴在执行一项引发该问题关键方面的任务时，背外侧前额叶皮层（dlPFC）中与功劳分配相关信息的神经元表征。我们发现神经元传递了功劳分配所需的信息。具体而言，神经元活动在反馈时反映了相关线索和结果，并且随着时间的推移以稳定的方式进行，这与之前关于dlPFC中表征不稳定的报道形成对比。此外，这些表征在学习早期最为稳定，而此时功劳分配最为需要。当功劳分配不需要相同特征时，这些神经元表征则要弱得多或不存在。这些结果表明，dlPFC神经元的活动符合执行功劳分配系统的基本要求，并且尖峰活动可以作为一种将因果联系起来的稳定机制。功劳分配是我们推断成功和失败原因的过程。我们发现背外侧前额叶皮层中的神经元活动传递了执行功劳分配所需的信息。重要的是，虽然存在各种随着时间保留因果事件“痕迹”的潜在机制，但我们观察到尖峰活动足够稳定，可以充当因果之间的联系，这与之前表明尖峰表征随时间不稳定的报道形成对比。此外，我们观察到这种稳定性随学习而变化，使得在最需要的早期学习过程中，神经编码随着时间的推移更加可靠。
