Song Joo-Hyun, McPeek Robert M
The Smith-Kettlewell Eye Research Inst., 2318 Fillmore St., San Francisco, CA 94115, USA.
J Neurophysiol. 2010 Apr;103(4):2124-38. doi: 10.1152/jn.00238.2009. Epub 2010 Feb 17.
Most visual scenes are complex and crowded, with several different objects competing for attention and action. Thus a complete understanding of the production of goal-directed actions must incorporate the higher-level process of target selection. To examine the neural substrates of target selection for visually guided reaching, we recorded the activity of isolated neurons in the dorsal premotor area (PMd) of monkeys performing a reaction-time visual search task. In this task, monkeys reached to an odd-colored target presented with three distractors. We found that PMd neurons typically discriminate the target before movement onset, ∼150-200 ms after the appearance of the search array. In one subset of neurons, discrimination occurred at a consistent time after search array onset regardless of when the reaching movement occurred, suggesting that these neurons are involved in target selection. In a second group of neurons, discrimination time depended on reach reaction time, consistent with involvement in movement production but not in target selection. To look for physiological corroboration of these two functionally defined groups, we analyzed the extracellular spike waveforms of recorded neurons. This analysis showed a population of neurons with narrow action potentials that carried signals related to target selection. A second population with broader action potentials was more heterogeneous, with some neurons showing activity related to target selection and others showing only movement production activity. These results suggest that PMd contains signals related to target selection and movement execution and that different signals are carried by distinct neural subpopulations.
大多数视觉场景都很复杂且拥挤，有几个不同的物体在争夺注意力和行动导向。因此，对目标导向行动产生的完整理解必须纳入目标选择的高级过程。为了研究视觉引导伸手动作中目标选择的神经基础，我们记录了猴子在执行反应时视觉搜索任务时背侧运动前区（PMd）中单个神经元的活动。在这个任务中，猴子伸手去够一个与三个干扰物一起呈现的颜色怪异的目标。我们发现，PMd神经元通常在运动开始前，即搜索阵列出现后约150 - 200毫秒时辨别目标。在一部分神经元中，无论伸手动作何时发生，辨别都在搜索阵列开始后的一个固定时间出现，这表明这些神经元参与目标选择。在第二组神经元中，辨别时间取决于伸手反应时间，这与参与运动产生而非目标选择一致。为了寻找这两个功能定义组的生理学证据，我们分析了记录神经元的细胞外尖峰波形。该分析显示了一群具有窄动作电位的神经元，它们携带与目标选择相关的信号。另一群具有更宽动作电位的神经元则更加异质，一些神经元显示与目标选择相关的活动，而另一些仅显示运动产生活动。这些结果表明，PMd包含与目标选择和运动执行相关的信号，并且不同的信号由不同的神经亚群携带。
