Neural correlates of a spatial sensory-to-motor transformation in primary motor cortex
Neural correlates of a spatial sensory-to-motor transformation in primary motor cortex
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DOI：
10.1152/jn.1997.77.3.1171
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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
初级运动皮层（MC）与运动加工密切相关，但很少有人试图确定MC是否也在感觉或上下文相关的加工中发挥作用。在本研究中，MC中的神经元活动的特征与视觉指示的肢体运动的规划和执行相关，这些运动的轨迹与其空间目标无关。这种设计允许与运动处理相关的神经元活动与感觉或上下文相关处理相关的活动分离。两个猕猴进行训练，以执行视觉指示，延迟达到的范例与间接视觉反馈。受试者使用右前肢捕捉视频显示器上的目标，通过移动二维操纵杆，其位置由光标反映。在每次试验中要捕获的目标由视觉指令刺激（IS）指示，该视觉指令刺激通过可变延迟与运动触发刺激（TS）分开。通过在两种条件下改变操纵杆和光标之间的空间映射，将前肢运动的方向与目标的位置分离，即未旋转（光标和肢体方向之间的0度偏移）和旋转（90度偏移）。任务相关的活动记录从总共180 MC神经元。本研究的重点是定向调谐的神经元活动，包括阶段性的，刺激相关的活动后，IS;紧张，设置相关的活动之间的IS和TS;和阶段性的，运动相关的活动后，TS。在具有定向调谐活动的MC神经元的整个样本中，在两种旋转条件下测试了119个细胞，允许依赖于目标位置的定向反应与依赖于肢体轨迹的定向反应分离。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两种条件下，共变和肢体依赖性，如果它只与肢体轨迹共变。由于旋转条件的变化，不符合目标或肢体依赖性标准的定向活动被归类为复杂活动。大约四分之一的MC神经元表现出弱的，但一致的，刺激相关的活动，定向调谐（24%，29 119）。几乎所有可定向分类的刺激相关活动都是靶点依赖性的（94%，15/16），只有一个肢体依赖性反应除外（6%，1/16）。大多数的MC神经元表现出设置相关的活动，定向调谐（61%，72 119）。在定向可分类的集合相关活动中，目标依赖性（37%，43例中的16例）和肢体依赖性反应（35%，43例中的15例）的数量相当，其余为复杂反应（27%，43例中的12例）。TS后的运动相关活动被认为是早期或晚期，这取决于它是在运动开始之前还是之后。大多数MC神经元表现出定向调节的早期运动相关活动（86%，102/119）：在那些神经元早期活动可定向分类的人中，只有三分之一的目标依赖性反应（14%，11/79）为肢体依赖性反应（43%，79人中的34人），其余为复杂型（43%，79个中的34个）。也有大多数MC神经元显示定向调谐的晚期运动相关活动（84%，100/119）：在晚期活动可定向分类的患者中，靶依赖性反应（5%，4/88）仅为肢体依赖性反应（41%，36/88）的九分之一，其余为复杂反应（55%，48/88）。在这项研究中所采用的指示延迟任务需要一个感官到运动的转换，通过该指示的目标位置与肢体运动的适当方向。在IS和运动反应之间的时间间隔延长，我们观察到目标依赖性活动的频率逐渐下降，肢体依赖性和复杂活动的频率逐渐增加。这表明，MC神经元可能在介导任务所需的空间感觉到运动转换中发挥作用。在这项研究中观察到的目标依赖性活动的相当大的比例，加强了越来越多的证据表明，至少有一些MC神经元发挥作用，无论是感觉或上下文相关的空间信息处理相关的特定运动任务。
Primary motor cortex (MC) has been strongly implicated in motor processing, but there have been relatively few attempts to determine whether MC may also play a role in either sensory or context-dependent processing. In the present study, neuronal activity in MC was characterized in relation to the planning and execution of visually instructed limb movements whose trajectories were dissociated from their spatial targets. This design permitted the dissociation of neuronal activity related to motor processing from activity related to sensory or context-dependent processing. Two macaque monkeys were trained to perform a visually instructed, delayed reaching paradigm with indirect visual feedback. Subjects used the right forelimb to capture targets presented on a video display by moving a two-dimensional joystick whose position was reflected by a cursor. The target to be captured on each trial was indicated by a visual instruction stimulus (IS), which was separated from a movement-triggering stimulus (TS) by a variable delay. The direction of forelimb movement was dissociated from the location of the target by varying the spatial mappings between joystick and cursor across two conditions, unrotated (0 degrees offset between cursor and limb direction) and rotated (90 degrees offset). Task-related activity was recorded from a total of 180 MC neurons. The focus of this study was on directionally tuned neuronal activity that included phasic, stimulus-related activity following the IS; tonic, set-related activity between IS and TS; and phasic, movement-related activity following the TS. Of the entire sample of MC neurons with directionally tuned activity, 119 cells were tested under both rotation conditions, permitting dissociation of directional responses that depended on target location from those that depended on limb trajectory. 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 did not fulfill the criteria for either target or limb dependence, because of changes across rotation conditions, was classified as complex. Approximately one quarter of MC neurons showed weak, but consistent, stimulus-related activity that was directionally tuned (24%, 29 of 119). Nearly all of the directionally classifiable stimulus-related activity was target dependent (94%, 15 of 16 responses), with the exception of a single limb-dependent response (6%, 1 of 16). A majority of MC neurons showed set-related activity that was directionally tuned (61%, 72 of 119). Of the directionally classifiable set-related activity, there were comparable numbers of target-dependent (37%, 16 of 43) and limb-dependent responses (35%, 15 of 43), with the remainder being complex (27%, 12 of 43). Movement-related activity following the TS was considered to be early or late, depending on whether it preceded or followed the onset of movement. The large majority of MC neurons showed early movement-related activity that was directionally tuned(86%, 102 of 119): among those whose neurons early activity was directionally classifiable, there were only one third as many target-dependent responses (14%, 1 1 of 79) as limb-dependent responses (43%, 34 of 79), with the remainder being complex (43%, 34 of 79).There was also a large majority of MC neurons that showed late movement-related activity that was directionally tuned (84%, 100 of 119): among those whose late activity was directionally classifiable, there were only one ninth as many target-dependent responses (5%, 4 of 88) as there were limb-dependent responses (41%, 36 of 88), with the remainder being complex (55%, 48 of 88). The instructed delay task employed in this study required a sensory-to-motor transformation through which the instructed target location was associated with a limb movement of the appropriate direction. Over the extended interval between IS and motor response, we observed a gradual decline in the frequency of target-dependent activity and gradual increases in the respective frequencies of both limb-dependent and complex activity. This suggests that MC neurons may play a role in mediating the spatial sensory-to-motor transformation required by the task. The substantial proportions of target-dependent activity observed in this study reinforce the growing evidence that at least some MC neurons do play a role in either sensory or context-dependent processing of spatial information relevant to specific motor tasks.