Opris Ioan, Lebedev Mikhail, Nelson Randall J
Department of Physiology and Pharmacology, Wake Forest University Winston Salem, NC, USA.
Front Neurosci. 2011 May 9;5:61. doi: 10.3389/fnins.2011.00061. eCollection 2011.
Although reward probability is an important factor that shapes animal's behavior, it is not well understood how the brain translates reward expectation into the vigor of movement [reaction time (RT) and speed]. To address this question, we trained two monkeys in a RT task that required wrist movements in response to vibrotactile and visual stimuli, with a variable reward schedule. Correct performance was rewarded in 75% of the trials. Monkeys were certain that they would be rewarded only in the trials immediately following withheld rewards. In these trials, the animals responded sooner and moved faster. Single-unit recordings from the dorsal striatum revealed modulations in neural firing that reflected changes in movement vigor. First, in the trials with certain rewards, striatal neurons modulated their firing rates earlier. Second, magnitudes of changes in neuronal firing rates depended on whether or not monkeys were certain about the reward. Third, these modulations depended on the sensory modality of the cue (visual vs. vibratory) and/or movement direction (flexions vs. extensions). We conclude that dorsal striatum may be a part of the mechanism responsible for the modulation of movement vigor in response to changes of reward predictability.
尽管奖励概率是塑造动物行为的一个重要因素，但大脑如何将奖励预期转化为运动活力（反应时间和速度）仍未得到充分理解。为了解决这个问题，我们训练了两只猴子完成一项反应时间任务，该任务要求猴子根据振动触觉和视觉刺激做出腕部运动，奖励计划是可变的。75%的试验中正确表现会得到奖励。猴子只有在紧接着无奖励试验之后的试验中才确定会得到奖励。在这些试验中，动物反应更快且移动速度更快。来自背侧纹状体的单神经元记录显示神经放电的调制反映了运动活力的变化。首先，在有确定奖励的试验中，纹状体神经元更早地调制其放电率。其次，神经元放电率变化的幅度取决于猴子是否确定会得到奖励。第三，这些调制取决于线索的感觉模态（视觉与振动）和/或运动方向（屈曲与伸展）。我们得出结论，背侧纹状体可能是负责响应奖励可预测性变化而调制运动活力的机制的一部分。
