Department of Neurobiology, University of Pittsburgh, Pittsburgh, United States.
Systems Neuroscience Center, University of Pittsburgh, Pittsburgh, United States.
Elife. 2023 Oct 19;12:e83196. doi: 10.7554/eLife.83196.
Frontal motor areas are central to controlling voluntary movements. In non-human primates, the motor areas contain independent, somatotopic, representations of the forelimb (i.e., motor maps). But are the neural codes for actions spatially organized within those forelimb representations? Addressing this question would provide insight into the poorly understood structure-function relationships of the cortical motor system. Here, we tackle the problem using high-resolution optical imaging and motor mapping in motor (M1) and dorsal premotor (PMd) cortex. Two macaque monkeys performed an instructed reach-to-grasp task while cortical activity was recorded with intrinsic signal optical imaging (ISOI). The spatial extent of activity in M1 and PMd was then quantified in relation to the forelimb motor maps, which we obtained from the same hemisphere with intracortical microstimulation. ISOI showed that task-related activity was concentrated in patches that collectively overlapped <40% of the M1 and PMd forelimb representations. The spatial organization of the patches was consistent across task conditions despite small variations in forelimb use. Nevertheless, the largest condition differences in forelimb use were reflected in the magnitude of cortical activity. Distinct time course profiles from patches in arm zones and patches in hand zones suggest functional differences within the forelimb representations. The results collectively support an organizational framework wherein the forelimb representations contain subzones enriched with neurons tuned for specific actions. Thus, the often-overlooked spatial dimension of neural activity appears to be an important organizing feature of the neural code in frontal motor areas.
额前运动区是控制自主运动的核心。在非人类灵长类动物中，运动区包含独立的、躯体定位的前肢（即运动图）代表。但是，动作的神经代码是否在这些前肢代表中空间组织？解决这个问题将有助于深入了解皮质运动系统中结构功能关系。在这里，我们使用高分辨率的光学成像和运动（M1）和背侧运动前区（PMd）皮层中的运动映射来解决这个问题。两只猕猴在进行指示性伸手抓握任务时，用内在信号光学成像（ISOI）记录皮质活动。然后，我们从同一半球的皮层内微刺激获得的前肢运动图来量化 M1 和 PMd 中的活动的空间范围。ISOI 显示，与任务相关的活动集中在斑块上，这些斑块总共重叠了 M1 和 PMd 前肢代表区的<40%。尽管前肢使用存在微小变化，但斑块的空间组织在各种任务条件下都是一致的。然而，前肢使用的最大条件差异反映在皮质活动的幅度上。臂区斑块和手区斑块的不同时程分布表明，前肢代表区存在功能差异。结果共同支持一种组织框架，即前肢代表区包含富含对特定动作敏感的神经元的亚区。因此，神经活动的空间维度似乎是额前运动区神经代码的一个重要组织特征，而这一维度经常被忽视。
