Stout John J, Griffin Amy L
Griffin Laboratory, Department of Psychological and Brain Sciences, University of Delaware, Newark, DE, United States.
Front Behav Neurosci. 2020 Aug 31;14:151. doi: 10.3389/fnbeh.2020.00151. eCollection 2020.
Spatial working memory (SWM) requires the encoding, maintenance, and retrieval of spatially relevant information to guide decision-making. The medial prefrontal cortex (mPFC) has long been implicated in the ability of rodents to perform SWM tasks. While past studies have demonstrated that mPFC ensembles reflect past and future experiences, most findings are derived from tasks that have an experimental overlap between the encoding and retrieval of trajectory specific information. In this study, we recorded single units from the mPFC of rats as they performed a T-maze delayed non-match to position (DNMP) task. This task consists of an encoding dominant sample phase, a memory maintenance delay period, and retrieval dominant choice phase. Using a linear classifier, we investigated whether distinct ensembles collectively reflect various trajectory-dependent experiences. We find that a population of high-firing rate mPFC neurons both predict a future choice and reflect changes in trajectory-dependent behaviors. We then developed a modeling procedure that estimated the number of high and low-firing rate units required to dissociate between various experiences. We find that low firing rate ensembles weakly reflect the direction that rats were forced to turn on the sample phase. This was in contrast to the highly active population that could effectively predict both future decision-making on early stem traversals and trajectory-divergences at T-junction. Finally, we compared the ensemble size necessary to code a forced trajectory to the size required to predict a decision. We provide evidence to suggest that a larger number of highly active neurons are employed during decision-making processes when compared to rewarded forced behaviors. Together, our study provides important insight into how specific ensembles of mPFC units support upcoming choices and ongoing behavior during SWM.
空间工作记忆（SWM）需要对空间相关信息进行编码、维持和检索，以指导决策。长期以来，内侧前额叶皮层（mPFC）一直被认为与啮齿动物执行SWM任务的能力有关。虽然过去的研究表明，mPFC神经元集群反映过去和未来的经历，但大多数发现都来自于在轨迹特定信息的编码和检索之间存在实验重叠的任务。在本研究中，我们在大鼠执行T迷宫延迟位置不匹配（DNMP）任务时，记录了其mPFC的单个神经元活动。该任务包括一个以编码为主的样本阶段、一个记忆维持延迟期和一个以检索为主的选择阶段。我们使用线性分类器，研究了不同的神经元集群是否共同反映了各种与轨迹相关的经历。我们发现，一群高 firing 率的mPFC神经元既能预测未来的选择，又能反映与轨迹相关行为的变化。然后，我们开发了一种建模程序，估计区分各种经历所需的高 firing 率和低 firing 率单元的数量。我们发现，低 firing 率的神经元集群对大鼠在样本阶段被迫转向的方向反映较弱。这与高度活跃的神经元群体形成对比，后者能够有效地预测早期干路穿越时的未来决策以及T形路口处的轨迹分歧。最后，我们比较了编码强制轨迹所需的神经元集群大小与预测决策所需的大小。我们提供的证据表明，与奖励性强制行为相比，决策过程中使用了更多数量的高度活跃神经元。总之，我们的研究为mPFC单元的特定集群如何在SWM期间支持即将到来的选择和正在进行的行为提供了重要见解。
