Hadjidimitrakis Kostas, Bertozzi Federica, Breveglieri Rossella, Galletti Claudio, Fattori Patrizia
Department of Pharmacy and Biotechnology, University of Bologna, Piazza di Porta San Donato 2, 40126, Bologna, Italy.
Department of Physiology, Monash University, Clayton, VIC, 3800, Australia.
Brain Struct Funct. 2017 May;222(4):1959-1970. doi: 10.1007/s00429-016-1319-5. Epub 2016 Oct 1.
Neurons in the posterior parietal cortex of macaques show spatial tuning during several phases of an instructed delay reaching task, but their reference frames have been studied mostly during fixed periods without addressing how they evolve across task phases. In parietal area V6A, we reported recently that during the late delay and hand movement periods, most neurons represent target location either in body-centered frame of reference, or in mixed body/hand-centered coordinates, with no evidence of hand-centered representations. Here, we characterized the spatial representations of V6A neurons in earlier task epochs, i.e., immediately after target fixation and in the subsequent main part of the delay and examined whether the reference frames of individual neurons are stable across the task. We report no evidence of hand-centered coding also in the earlier phases of the task. Shortly, after target fixation and throughout the main part of the delay period, V6A neurons used either body-centered or mixed body/hand-centered reference frames. Most of the cells showed consistent reference frames across epochs. Interestingly, a population trend of shifting from mixed body/hand-centered frames to 'pure' body-centered coordinates was found as the task progressed. These findings suggest that, similar to other parietal areas, in V6A, the reference frames show a limited degree of temporal evolution. The stronger presence of mixed coding at the early task stages could reflect the early involvement of V6A in eye-hand coordination, whereas the increase in spatiotopic representations towards movement execution could be related to its role in online movement control.
猕猴后顶叶皮层中的神经元在指令延迟伸手任务的几个阶段表现出空间调谐，但它们的参考系大多是在固定时间段内进行研究的，并未探讨其在任务各阶段是如何演变的。在顶叶V6A区，我们最近报道，在延迟后期和手部运动阶段，大多数神经元以身体中心参考系或身体/手部混合中心坐标来表征目标位置，没有以手部中心表征的证据。在此，我们对V6A神经元在任务早期阶段（即目标固定后立即以及随后延迟的主要部分）的空间表征进行了特征描述，并研究了单个神经元的参考系在整个任务过程中是否稳定。我们发现在任务的早期阶段也没有以手部中心编码的证据。在目标固定后不久以及整个延迟期的主要部分，V6A神经元使用身体中心或身体/手部混合中心参考系。大多数细胞在各阶段表现出一致的参考系。有趣的是，随着任务的推进，发现了一种从身体/手部混合中心参考系向“纯粹”身体中心坐标转变的群体趋势。这些发现表明，与其他顶叶区域类似，在V6A区，参考系表现出有限程度的时间演变。任务早期阶段混合编码的更强存在可能反映了V6A在眼手协调中的早期参与，而向运动执行阶段空间拓扑表征的增加可能与其在在线运动控制中的作用有关。
