Donders Institute for Brain, Cognition, and Behavior, Radboud University Nijmegen, 6500 HB Nijmegen, The Netherlands.
J Neurosci. 2013 Apr 10;33(15):6492-503. doi: 10.1523/JNEUROSCI.3928-12.2013.
Two parietofrontal networks share the control of goal-directed movements: a dorsomedial circuit that includes the superior parieto-occipital sulcus (sPOS) and a dorsolateral circuit comprising the anterior intraparietal sulcus (aIPS). These circuits are thought to independently control either reach and grip components (a functional dissociation), or planning and execution phases of grasping movements (a temporal dissociation). However, recent evidence of functional and temporal overlap between these circuits has undermined those models. Here, we test an alternative model that subsumes previous accounts: the dorsolateral and dorsomedial circuits operate at different hierarchical levels, resulting in functional and temporal dependencies between their computations. We asked human participants to grasp a visually presented object, manipulating movement complexity by varying object slant. We used concurrent single-pulse transcranial magnetic stimulation and electroencephalography (TMS-EEG) to probe and record neurophysiological activity in the two circuits. Changes in alpha-band oscillations (8-12 Hz) characterized the effects of task manipulations and TMS interferences over aIPS and sPOS. Increasing the complexity of the grasping movement was accompanied by alpha-suppression over dorsomedial parietofrontal regions, including sPOS, during both planning and execution stages. TMS interference over either aIPS or sPOS disrupted this index of dorsomedial computations; early when aIPS was perturbed, later when sPOS was perturbed, indicating that the dorsomedial circuit is temporally dependent on aIPS. TMS over sPOS enhanced alpha-suppression in inferior parietal cortex, indicating that the dorsolateral circuit can compensate for a transient sPOS perturbation. These findings suggest that both circuits specify the same grasping parameters, with dorsomedial computations depending on dorsolateral contributions.
一个包括上顶枕沟（sPOS）的背内侧回路和一个由前内顶沟（aIPS）组成的背外侧回路。这些回路被认为可以独立控制伸手和抓握组件（功能分离），或者抓握运动的规划和执行阶段（时间分离）。然而，最近关于这些回路之间存在功能和时间重叠的证据，破坏了这些模型。在这里，我们测试了一个替代模型：背外侧和背内侧回路在不同的层次上运作，导致它们的计算之间存在功能和时间依赖性。我们要求人类参与者抓住一个视觉呈现的物体，通过改变物体的倾斜来改变运动的复杂性。我们使用同时进行的单次经颅磁刺激和脑电图（TMS-EEG）来探测和记录两个回路中的神经生理活动。alpha 波段振荡（8-12Hz）的变化特征是任务操作和 TMS 干扰对 aIPS 和 sPOS 的影响。增加抓握运动的复杂性伴随着背侧额顶叶区域的 alpha 抑制，包括 sPOS，在规划和执行阶段都有。TMS 干扰 aIPS 或 sPOS 都会破坏背内侧计算的这个指标；当 aIPS 受到干扰时较早，当 sPOS 受到干扰时较晚，这表明背内侧回路在时间上依赖于 aIPS。sPOS 上的 TMS 增强了下顶叶皮层的 alpha 抑制，表明背外侧回路可以补偿暂时的 sPOS 干扰。这些发现表明，两个回路都指定了相同的抓握参数，背内侧计算依赖于背外侧回路的贡献。
