Department of Neuroscience, University of Montréal, Montréal, Québec, Canada.
J Neurophysiol. 2020 Mar 1;123(3):927-935. doi: 10.1152/jn.00682.2019. Epub 2020 Jan 29.
Humans and other animals are faced with decisions about actions on a daily basis. These typically include a period of deliberation that ends with the commitment to a choice, which then leads to the overt expression of that choice through action. Previous studies with monkeys have demonstrated that neural activity in sensorimotor areas correlates with the deliberation process and reflects the moment of commitment before movement initiation, but the causal roles of these regions are challenging to establish. Here, we tested whether dorsal premotor (PMd) and primary motor cortex (M1) are causally involved in the volitional commitment to a reaching choice. We found that brief subthreshold microstimulation in PMd or M1 delayed commitment to an action but not the initiation of the action itself. Importantly, microstimulation only had a significant effect when it was delivered close to and before commitment time. These results are consistent with the proposal that PMd and M1 participate in the commitment process, which occurs when a critical firing rate difference is reached between cells voting for the selected option and those voting for the competing one. The neural substrates of decisions between actions are typically investigated by correlating neural activity and subjects' decision behavior, but this does not establish causality. In a reaching decision task, we demonstrate that subthreshold microstimulation of the monkey dorsal premotor cortex or primary motor cortex delays the deliberation duration if applied shortly before choice commitment. This result suggests a causal role of the sensorimotor cortex in the determination of decisions between actions.
人类和其他动物每天都要面对关于行动的决策。这些决策通常包括一段时间的深思熟虑，最终做出选择的承诺，然后通过行动来表达选择。之前对猴子的研究表明，感觉运动区域的神经活动与深思熟虑过程相关，并反映了在运动开始之前的承诺时刻，但这些区域的因果作用难以确定。在这里，我们测试了背侧运动前皮质（PMd）和初级运动皮质（M1）是否在自愿承诺进行伸手选择方面具有因果关系。我们发现，PMd 或 M1 的短暂阈下微刺激会延迟对动作的承诺，但不会延迟动作本身的开始。重要的是，只有在接近并在承诺时间之前进行微刺激时，微刺激才会产生显著效果。这些结果与 PMd 和 M1 参与承诺过程的提议一致，该过程发生在为选定选项投票的细胞和为竞争选项投票的细胞之间达到关键的发射率差异时。动作之间决策的神经基质通常通过关联神经活动和受试者的决策行为来研究，但这并不能确定因果关系。在伸手决策任务中，我们证明如果在选择承诺之前不久应用猴子背侧运动前皮质或初级运动皮质的阈下微刺激，则会延长深思熟虑的持续时间。这个结果表明感觉运动皮层在动作之间的决策中起着因果作用。
