演題番号 : S1-10-1-1
松本 正幸 / Masayuki Matsumoto:1
1:京大・霊長研・統合脳システム / Systems Neuroscience Section, Primate Research Institute, Kyoto University, Inuyama, Japan
Midbrain dopamine neurons are excited by reward and inhibited by reward omission. These excitatory and inhibitory signals have been implicated in learning and motivation. However, it was unclear which parts of the brain provide dopamine neurons with reward-related signals necessary for their responses. Recent studies provided evidence that the lateral habenula (LHb) is a good candidate for a source of the reward-related signals in dopamine neurons. The LHb projects to the substantia nigra pars compacta and ventral tegmental area which contain dopamine neurons. Electrical stimulation of the LHb inhibits dopamine neuron activity. LHb neurons also respond to reward and reward omission but in an opposite manner to dopamine neurons (i.e., they are inhibited by reward and excited by reward omission). In this talk, I will present our recent data examining the function of the LHb signals. We first recorded the activity of LHb neurons in monkeys during a Pavlovian conditioning with appetitive and aversive outcomes. We found that LHb neurons were most strongly excited by a conditioned stimulus predicting the most unpleasant event such as the absence of reward or the presence of aversive airpuff, suggesting negative value coding by these neurons. To further examine the role of the value signal in behavior, we next artificially activated the LHb by electrical stimulation while monkeys were performing a visually guided saccade task. The target was presented randomly on the right or left and the monkey had to make a saccade to it immediately. Saccades to one direction were followed by electrical stimulation of the LHb while saccades to the other direction were not. We found that the latency of the saccade associated with the LHb stimulation increased gradually as the saccade was repeatedly followed by the stimulation. This gradual increase in latency suggests that the activity of the LHb contributes to learning to suppress behaviors which would lead to unpleasant events.