Temporal Information Processing in Prefrontal-Basal Ganglia Circuit

我们一直在进行神经生理学实验，以揭示前额基底节回路中处理时间信息的神经元机制。研究人员训练猴子执行时长辨别任务。在该任务中，两个视觉线索在不同的持续时间(0.2~1.6秒)内被连续呈现。每次提示之后都会有1秒的延迟期。在第二个延迟期之后，受试者被指示选择一个更长的提示。在猴子完成这项任务时，前额叶皮质和纹状体记录到了单个单位的活动。前额叶神经元在第一个线索阶段显示出相位活动。活动的峰值时间在800ms左右，接近长、短线索持续时间的中点。这一活动可能起到了过滤线索持续时间的作用，以区分长线索和短线索。在第一个延迟期，前额叶神经元在长线索和短线索后表现出不同的活动。在偏爱长线索的神经元中，无论线索持续时间长短，长线索后的延迟活动一致较高，而较短线索后的延迟活动一致较低。这种延迟活动的二元变化表明，前额叶皮质可以明确地代表线索持续时间的长或短。纹状体神经元在第一和第二延迟期有相性反应。第一延迟时段内的响应根据第一提示持续时间而改变。这些神经元群体的活动与第一次线索持续时间呈正相关或负相关。在第二个延迟期内，长-短和短-长试验的反应不同。这些发现表明，纹状体神经元可以通过单调变化的反应和两种线索持续时间之间的区分结果来编码线索持续时间。

We have been conducting neurophysiological experiments to reveal neuronal mechanisms for temporal information processing in the prefrontal-basal ganglia circuit. Monkeys were trained to perform a duration discrimination task. In the task, two visual cues were presented successively in different duration (0.2〜1.6 sec). Each cue presentation was followed by a 1-sec delay period. The subjects were instructed to choose a longer presented cue after the second delay period. Single-unit activity was recorded from the prefrontal cortex and the striatum while the monkeys were performing the task.Prefrontal neurons showed phasic activity during the first cue period. The activity had peak time around 800ms that was close to the midpoint between long and short cue duration. This activity might have functioned for filtering cue duration to discriminate between long and short cues. In the first delay period prefrontal neurons exhibited differential activity following long and short cues. In the neurons with preference for long cues the delay activity after longer cues was uniformly high regardless of cue duration, but that after shorter cues was uniformly low. This binary change in the delay activity indicates that the prefrontal cortex could represent cue duration categorically as long or short. Striatal neurons phasically responded during the first and second delay periods. Responses during the first delay period changed depending on the first cue duration. Activity of populations of these neurons correlated with the first cue duration positively or negatively. Responses during the second delay period differed between long-short and short-long trials. These findings suggest that striatal neurons could encode cue duration with monotonically changing responses and discrimination results between the two cue durations.