Okada Ken-ichi, Toyama Keisuke, Inoue Yuka, Isa Tadashi, Kobayashi Yasushi
Graduate School of Frontier Biosciences, Osaka University, Toyonaka 560-8531, Japan.
J Neurosci. 2009 Apr 15;29(15):4858-70. doi: 10.1523/JNEUROSCI.4415-08.2009.
The dopamine system has been implicated in guiding behavior based on rewards. The pedunculopontine tegmental nucleus (PPTN) of the brainstem receives afferent inputs from reward-related structures, including the cerebral cortices and the basal ganglia, and in turn provides strong excitatory projections to dopamine neurons. This anatomical evidence predicts that PPTN neurons may carry reward information. To elucidate the functional role of the PPTN in reward-seeking behavior, we recorded single PPTN neurons while monkeys performed a visually guided saccade task in which the predicted reward value was informed by the shape of the fixation target. Two distinct groups of neurons, fixation target (FT) and reward delivery (RD) neurons, carried reward information. The activity of FT neurons persisted between FT onset and reward delivery, with the level of activity associated with the magnitude of the expected reward. RD neurons discharged phasically after reward delivery, with the levels of activity associated with the actual reward. These results suggest that separate populations of PPTN neurons signal predicted and actual reward values, both of which are necessary for the computation of reward prediction error as represented by dopamine neurons.
多巴胺系统被认为在基于奖励的行为引导中发挥作用。脑干的脚桥被盖核（PPTN）接收来自包括大脑皮层和基底神经节在内的与奖励相关结构的传入输入，进而向多巴胺神经元提供强烈的兴奋性投射。这一解剖学证据表明，PPTN神经元可能携带奖励信息。为了阐明PPTN在寻求奖励行为中的功能作用，我们在猴子执行视觉引导的扫视任务时记录单个PPTN神经元的活动，在该任务中，注视目标的形状告知预期奖励值。两类不同的神经元，即注视目标（FT）神经元和奖励发放（RD）神经元，携带奖励信息。FT神经元的活动在FT出现到奖励发放之间持续存在，其活动水平与预期奖励的大小相关。RD神经元在奖励发放后出现相位性放电，其活动水平与实际奖励相关。这些结果表明，PPTN神经元的不同群体分别信号化预测和实际奖励值，这两者对于由多巴胺神经元所代表的奖励预测误差的计算都是必需的。
