Averbeck Bruno B, Crowe David A, Chafee Matthew V, Georgopoulos Apostolos P
Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, UK.
Cortex. 2009 Mar;45(3):432-41. doi: 10.1016/j.cortex.2008.02.007. Epub 2008 Jun 14.
In this study we examined the differential contribution of superior parietal cortex (SPC) and caudal dorsal-lateral prefrontal cortex (dlPFC) to drawing geometrical shapes. Monkeys were trained to draw triangles, squares, trapezoids and inverted triangles while we recorded the activity of small ensembles of neurons in caudal area 46 and areas 5 and 2 of parietal cortex. We analyzed the drawing factors encoded by individual neurons by fitting a step-wise general-linear model using as our dependent variable the firing rate averaged over segments of the produced trajectories. This analysis demonstrated that both cognitive (shape and segment serial position) and motor (maximum speed, position and direction of segment) factors modulated the activity of individual neurons. Furthermore, SPC had an enriched representation of both shape and motor factors, with the motor enrichment being stronger than the shape enrichment. Following this we used the activity in the simultaneously recorded neural ensembles to predict the hand velocity. In these analyses we found that the prediction of the hand velocity was better when we estimated different linear decoding functions for each shape than when we estimated a single function across shapes, although it was a subtle effect. Furthermore, we also found that ensembles of caudal dlPFC neurons carried considerable information about hand velocity, a purely motor factor. However, the SPC ensembles carried more information at the ensemble level as a function of the ensemble size than the caudal dlPFC ensembles, although the differences were not dramatic. Finally, an analysis of the response latencies of individual neurons showed that the caudal dlPFC representation was more sensory than the SPC representation, which was equally sensory and motor. Thus, this neurophysiological evidence suggests that both SPC and caudal dlPFC have a role in drawing, but that SPC plays a larger role in both the cognitive and the motor components.
在本研究中，我们考察了顶叶上区（SPC）和尾侧背外侧前额叶皮质（dlPFC）在绘制几何形状方面的不同作用。我们训练猴子绘制三角形、正方形、梯形和倒三角形，同时记录顶叶皮质尾侧46区以及5区和2区中小群神经元的活动。我们通过拟合一个逐步通用线性模型来分析单个神经元编码的绘图因素，该模型将生成轨迹各段的平均放电率作为因变量。这一分析表明，认知因素（形状和片段序列位置）和运动因素（片段的最大速度、位置和方向）均能调节单个神经元的活动。此外，SPC对形状和运动因素都有丰富的表征，其中运动表征比形状表征更强。在此之后，我们利用同时记录的神经集群活动来预测手部速度。在这些分析中，我们发现，当针对每种形状估计不同的线性解码函数时，对手部速度的预测要优于估计一个跨形状的单一函数时，尽管这是一个微妙的效应。此外，我们还发现，尾侧dlPFC神经元集群携带了关于手部速度的大量信息，这是一个纯粹的运动因素。然而，SPC集群在集群水平上作为集群大小的函数携带的信息比尾侧dlPFC集群更多，尽管差异并不显著。最后，对单个神经元反应潜伏期的分析表明，尾侧dlPFC的表征比SPC的表征更具感觉性，而SPC则在感觉和运动方面表现相当。因此，这一神经生理学证据表明，SPC和尾侧dlPFC在绘图中都发挥了作用，但SPC在认知和运动成分中发挥的作用更大。
