Pantoja Janaina, Ribeiro Sidarta, Wiest Michael, Soares Ernesto, Gervasoni Damien, Lemos Nelson A M, Nicolelis Miguel A L
Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710, USA.
J Neurosci. 2007 Sep 26;27(39):10608-20. doi: 10.1523/JNEUROSCI.5279-06.2007.
Delayed-response sensory discrimination is believed to require primary sensory thalamus and cortex for early stimulus identification and higher-order forebrain regions for the late association of stimuli with rewarded motor responses. Here we investigate neuronal responses in the rat primary somatosensory cortex (S1) and ventral posterior medial nucleus of the thalamus (VPM) during a tactile discrimination task that requires animals to associate two different tactile stimuli with two corresponding choices of spatial trajectory to be rewarded. To manipulate reward expectation, neuronal activity observed under regular reward contingency (CR) was compared with neuronal activity recorded during freely rewarded (FR) trials, in which animals obtained reward regardless of their choice of spatial trajectory. Across-trial firing rates of S1 and VPM neurons varied according to the reward contingency of the task. Analysis of neuronal ensemble activity by an artificial neural network showed that stimulus-related information in S1 and VPM increased from stimulus sampling to reward delivery in CR trials but decreased to chance levels when animals performed FR trials, when stimulus discrimination was irrelevant for task execution. Neuronal ensemble activity in VPM was only correlated with task performance during stimulus presentation. In contrast, S1 neuronal activity was highly correlated with task performance long after stimulus removal, a relationship that peaked during the 300 ms that preceded reward delivery. Together, our results indicate that neuronal activity in the primary somatosensory thalamocortical loop is strongly modulated by reward contingency.
延迟反应感觉辨别被认为需要初级感觉丘脑和皮层来进行早期刺激识别，以及高阶前脑区域来进行刺激与奖励性运动反应的后期关联。在此，我们研究大鼠初级体感皮层（S1）和丘脑腹后内侧核（VPM）在一项触觉辨别任务中的神经元反应，该任务要求动物将两种不同的触觉刺激与两种相应的空间轨迹选择相关联以获得奖励。为了操纵奖励预期，我们将常规奖励条件（CR）下观察到的神经元活动与自由奖励（FR）试验期间记录的神经元活动进行比较，在自由奖励试验中，动物无论其空间轨迹选择如何都能获得奖励。S1和VPM神经元的跨试验放电率根据任务的奖励条件而变化。通过人工神经网络对神经元群体活动的分析表明，在CR试验中，S1和VPM中与刺激相关的信息从刺激采样到奖励发放时增加，但当动物进行FR试验时，当刺激辨别与任务执行无关时，该信息降至随机水平。VPM中的神经元群体活动仅在刺激呈现期间与任务表现相关。相比之下，S1神经元活动在刺激去除后很长时间内都与任务表现高度相关，这种关系在奖励发放前的300毫秒达到峰值。总之，我们的结果表明，初级体感丘脑皮质环路中的神经元活动受到奖励条件的强烈调节。
