Marzocchi Nicoletta, Breveglieri Rossella, Galletti Claudio, Fattori Patrizia
Dipartimento di Fisiologia Umana e Generale, Università di Bologna, I-40126 Bologna, Italy.
Eur J Neurosci. 2008 Feb;27(3):775-89. doi: 10.1111/j.1460-9568.2008.06021.x.
Parietal area V6A contains neurons modulated by the direction of gaze as well as neurons able to code the direction of arm movement. The present study was aimed to disentangle the gaze effect from the effect of reaching activity upon single V6A neurons. To this purpose, we used a visuomotor task in which the direction of arm movement remained constant while the animal changed the direction of gaze. Gaze direction modulated reach-related activity in about two-thirds of tested neurons. In several cases, modulations were not due to the eye-position signal per se, the apparent eye-position modulation being just an epiphenomenon. The real modulating factor was the location of reaching target with respect to the point gazed by the animal, that is, the retinotopic coordinates towards which the action of reaching occurred. Comparison of neural discharge of the same cell during execution of foveated and non-foveated reaching movements, performed towards the same or different spatial locations, confirmed that in a part of V6A neurons reaching activity is coded retinocentrically. In other neurons, reaching activity is coded spatially, depending on the direction of reaching movement regardless of where the animal was looking at. The majority of V6A reaching neurons use a system that encompasses both of these reference frames. These results are in line with the view of a progressive visuomotor transformation in the dorsal visual stream, that changes the frame of reference from the retinocentric one, typically used by the visual system, to the arm-centred one, typically used by the motor system.
顶叶V6A区包含受注视方向调制的神经元以及能够编码手臂运动方向的神经元。本研究旨在区分注视效应与到达活动对单个V6A神经元的影响。为此，我们使用了一种视觉运动任务，其中当动物改变注视方向时，手臂运动方向保持不变。注视方向在大约三分之二的测试神经元中调制了与到达相关的活动。在几种情况下，调制并非由于眼位信号本身，明显的眼位调制只是一种附带现象。真正的调制因素是到达目标相对于动物注视点的位置，即到达动作发生的视网膜坐标。对在向相同或不同空间位置进行中心凹注视和非中心凹注视到达运动执行期间同一细胞的神经放电进行比较，证实了在一部分V6A神经元中，到达活动是以视网膜中心编码的。在其他神经元中，到达活动是根据到达运动的方向进行空间编码的，而不管动物看向何处。大多数V6A到达神经元使用一种包含这两种参考框架的系统。这些结果与背侧视觉流中渐进的视觉运动转换观点一致，该转换将参考框架从视觉系统通常使用的视网膜中心参考框架转变为运动系统通常使用的以手臂为中心的参考框架。
