Sensory and Behavioural Neuroscience Unit, Okinawa Institute of Science and Technology Graduate University, Okinawa, Japan.
PLoS Biol. 2024 Mar 1;22(3):e3002536. doi: 10.1371/journal.pbio.3002536. eCollection 2024 Mar.
Associating values to environmental cues is a critical aspect of learning from experiences, allowing animals to predict and maximise future rewards. Value-related signals in the brain were once considered a property of higher sensory regions, but their wide distribution across many brain regions is increasingly recognised. Here, we investigate how reward-related signals begin to be incorporated, mechanistically, at the earliest stage of olfactory processing, namely, in the olfactory bulb. In head-fixed mice performing Go/No-Go discrimination of closely related olfactory mixtures, rewarded odours evoke widespread inhibition in one class of output neurons, that is, in mitral cells but not tufted cells. The temporal characteristics of this reward-related inhibition suggest it is odour-driven, but it is also context-dependent since it is absent during pseudo-conditioning and pharmacological silencing of the piriform cortex. Further, the reward-related modulation is present in the somata but not in the apical dendritic tuft of mitral cells, suggesting an involvement of circuit components located deep in the olfactory bulb. Depth-resolved imaging from granule cell dendritic gemmules suggests that granule cells that target mitral cells receive a reward-related extrinsic drive. Thus, our study supports the notion that value-related modulation of olfactory signals is a characteristic of olfactory processing in the primary olfactory area and narrows down the possible underlying mechanisms to deeper circuit components that contact mitral cells perisomatically.
将环境线索与价值联系起来是从经验中学习的一个关键方面，使动物能够预测和最大化未来的奖励。大脑中的价值相关信号曾经被认为是更高感官区域的属性，但它们在许多大脑区域中的广泛分布越来越被认识到。在这里，我们研究了奖励相关信号如何在嗅觉处理的最早阶段，即嗅球中，从机制上开始被纳入。在进行密切相关的嗅觉混合物的 Go/No-Go 辨别任务的头部固定小鼠中，奖励气味会在一类输出神经元中引起广泛的抑制，即在僧帽细胞中，但不在丛状细胞中。这种奖励相关抑制的时间特征表明它是气味驱动的，但它也是上下文依赖的，因为在假条件作用和梨状皮层药理学沉默期间它不存在。此外，奖励相关的调制存在于僧帽细胞的胞体中，但不存在于树突棘丛中，这表明涉及位于嗅球深部的回路成分。从颗粒细胞树突 gemmules 的深度分辨成像表明，靶向僧帽细胞的颗粒细胞接收到奖励相关的外在驱动。因此，我们的研究支持了这样一种观点，即嗅觉信号的价值相关调制是初级嗅觉区域嗅觉处理的一个特征，并将潜在的机制缩小到与僧帽细胞胞体接触的更深的回路成分。
