Preferential representation of instructed target location versus limb trajectory in dorsal premotor area
Preferential representation of instructed target location versus limb trajectory in dorsal premotor area
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DOI：
10.1152/jn.1997.77.3.1195
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发表时间：
1997-03-01
影响因子：
2.5
通讯作者：
Alexander, GE
中科院分区：
文献类型：
--
作者：
Shen, LM;Alexander, GE
猴子的背侧运动前区（PMd）参与运动准备和运动选择的过程。在本研究中，我们试图确定在延迟到达任务期间激活的PMd神经元是否具有反映目标（即，目标）或运动本身的物理特性。两个猕猴进行训练，以执行视觉指示，延迟达到任务与间接视觉反馈。主题和方法与前一篇论文中描述的相同。在行为任务中，每个受试者用右前肢移动一个二维操纵杆，将光标与视频显示器上的目标对齐。该范式将前肢运动的方向与目标的空间位置分离。这是通过改变操纵杆和光标之间的空间映射来实现的。一个可变的延迟分离的视觉刺激，指示的目标位置（IS）的视觉刺激，触发的指示运动（TS），任务相关的活动记录从总共181个PMd神经元。本研究的重点是定向调节的神经元反应，包括I）刺激相关活动（阶段性，IS之后）; 2）集合相关活动（强直性，IS和TS之间）;和3）运动相关活动（阶段性，TS之后）。在具有定向调谐活动的PMd神经元的整个样本中，114个用两个操纵杆/光标映射进行了测试，允许依赖于肢体轨迹的定向反应与依赖于目标位置的定向反应分离。任务相关的神经元活动被归类为目标依赖性，如果它只与目标位置在这两个条件下共变，和肢体依赖性，如果它只与肢体轨迹共变。在旋转条件下发生显著变化的方向活动被归类为复杂。大约一半的样本PMd神经元显示刺激相关的活动，定向调谐（56%，64 114）。几乎所有的定向分类的刺激相关的活动是目标依赖性（94%，44 47响应），没有肢体依赖性。一小部分被归类为复杂（6%，47份答复中有3份）。超过三分之二的PMd神经元显示出定向调谐的集合相关活动（69%，114个中的79个）。在具有可定向分类的集合相关活动的细胞中，靶依赖性反应（76%，63个中的48个）是肢体依赖性反应（8%，63个中的5个）的9倍，其余的是复杂的（16%，63个中的10个）。大约四分之三的PMd神经元样本显示出定向调谐的早期运动相关活动（运动开始前）（78%，89/114）。在那些早期运动相关活性可定向分类的细胞中，靶依赖性反应（51%，66个中的34个）是肢体依赖性反应（14%，66个中的9个）的3倍多，其余的是复杂的（35%，66个中的23个）。大约三分之二的样本表现出迟动相关反应（在运动开始后），（68%，114个中的78个）。在那些晚期运动相关活性可定向分类的细胞中，有相当数量的靶依赖性细胞。（25%，15/61）和肢体依赖性反应（28%，17/61），其余为复杂反应（47%，29/61）。这些结果表明，优先代表的目标位置，而不是肢体轨迹PMd神经元。在延长的间隔从IS到运动responses，有一个逐渐下降的频率的目标依赖性活动和相应的频率增加的肢体依赖性和复杂的活动。这些发现表明，PMd神经元可能参与介导延迟到达任务所需的感觉到运动的转换。比较PMd神经元与运动皮层神经元的反应记录在相同的实验对象表明，PMd可能发挥了优先的作用，在感觉或上下文相关的处理有关的任务性能，而运动皮层可能更多地参与处理有关的纯运动方面的任务性能。
The dorsal premotor area (PMd) of monkeys has been implicated in processes relating to movement preparation and movement selection. In the present study, we sought to determine whether PMd neurons that are activated during a delayed reaching task have directional responses that reflect either the target (i.e., the goal) of an intended movement or the physical properties of the movement itself. Two macaque monkeys were trained to perform a visually instructed, delayed reaching task with indirect visual feedback. The subjects and methods were identical to those described in the preceding paper. In the behavioral task, each subject moved a two-dimensional joystick with the right forelimb to align a cursor with targets presented on a video display. The paradigm dissociated the direction of forelimb movement from the spatial location of the target. This was accomplished by varying the spatial mappings between joystick and cursor. A variable delay separated the visual stimulus that instructed the target location (IS) from the visual stimulus that triggered the instructed movement (TS), Task-related activity was recorded from a total of 181 PMd neurons. The focus of this study was on directionally tuned neuronal responses that included I) stimulus-related activity (phasic, following IS); 2) set-related activity (tonic, between IS and TS); and 3) movement-related activity (phasic, following TS). Of the entire sample of PMd neurons with directionally tuned activity, 114 were tested with two joystick/cursor mappings, permitting dissociation of directional responses that depended on limb trajectory from those that depended on target location. Task-related neuronal activity was classified as target-dependent if it covaried exclusively with target location across both conditions, and as limb-dependent if it covaried exclusively with limb trajectory. Directional activity that changed significantly across rotation conditions was classified as complex. Approximately one half of the sample of PMd neurons showed stimulus-related activity that was directionally tuned (56%, 64 of 114). Nearly all of the directionally classifiable stimulus-related activity was target dependent (94%, 44 of 47 responses), and none was limb dependent. A small proportion was classified as complex (6%, 3 of 47 responses). More than two thirds of the PMd neurons showed set-related activity that was directionally tuned (69%, 79 of 114). Among cells with set-related activity that was directionally classifiable, there were similar to 9 times as many target-dependent responses (76%, 48 of 63) as there were limb-dependent responses (8%, 5 of 63), with the remainder being complex (16%, 10 of 63). Approximately three quarters of the sample of PMd neurons showed early movement-related activity (before movement onset) that was directionally tuned (78%, 89 of 114). Among those cells whose early movement-related activity was directionally classifiable, there were >3 times as many target-dependent responses (51%, 34 of 66) as limb-dependent responses (14%, 9 of 66), with the remainder being complex (35%, 23 of 66). Approximately two thirds of the sample showed late movement-related responses (after movement onset) that were directionally tuned (68%, 78 of 114).Among those cells whose late movement-related activity was directionally classifiable, there were comparable numbers of target-dependent (25%, 15 of 61) and limb-dependent responses (28%, 17 of 61), with the remainder being complex (47%, 29 of 61). These results indicate a preferential representation of target location rather than limb trajectory among PMd neurons.Over the extended interval from IS to motor response, there was a gradual decline in the frequency of target-dependent activity and corresponding increases in the frequencies of both limb-dependent and complex activity. These findings suggest that PMd neurons may participate in mediating the sensory-to-motor transformation required by the delayed reaching task. Comparison of the responses of PMd neurons with those of motor cortex neurons recorded in the same experimental subjects indicates that PMd may play a preferential role in sensory or context-dependent processing related to task performance, whereas motor cortex may be more involved in processing related to the purely motor aspects of task performance.