Summary: The lateral hypothalamus is an integral component of social brain networks. It shapes socially motivated behaviors via functional coordination with neocortical regions.
Source: National Institutes of Natural Sciences
How much we value an item is often related to what other people have. You might want the newest fashion, but not once everybody has it. Or, winning a free lunch at your favorite restaurant might not seem as great if the other person won a million dollars. Now, researchers in Japan have discovered a region of the brain that controls these kinds of behaviors in monkeys.
In their study published in Proceedings of the National Academy of Sciences, a team of researchers from the National Institutes of Natural Sciences in Okazaki, Japan show that when monkeys think other monkeys will be rewarded, their own rewards become less appealing. This was evident in the amount that monkeys licked their lips while waiting for their reward. The team found that licking increased the more monkeys anticipated receiving a reward and decreased as they anticipated the other monkey would receive it instead.
This behavior was reflected in the brain. As first author Atsushi Noritake explains, “We found a clear link between brain activity in the lateral hypothalamus and the licking behavior that represented subjective value of the reward.” The team recorded activity from neurons as monkeys saw pictures that indicated the chance that they or another monkey would receive a reward. The scientists found that for some cells, firing rates increased with the probability of receiving the reward and decreased with the probability that the other monkey would get the reward.
A second experiment showed that the same brain region was necessary for the social observations to affect how much the monkeys valued the reward. When the scientists temporarily shut down the lateral hypothalamus using an inhibitory drug, the monkeys’ licking behavior was unchanged when they anticipated receiving the reward themselves–it still increased with the chance of reward. However, the amount of licking was now unrelated to the chance of reward when they were cued that the other monkey was likely to get it.
This behavior was similar to what happened when the other monkey was prevented from getting the reward or when it was absent altogether.
“Without a functioning lateral hypothalamus, it was as if the monkeys no longer processed what they were seeing as a social situation,” says team leader Masaki Isoda. “Thus, we believe that the lateral hypothalamus is necessary for shaping socially motivated behavior, perhaps in coordination with other brain areas such as the medial prefrontal cortex.”
Representation of distinct reward variables for self and other in primate lateral hypothalamus
The lateral hypothalamus (LH) has long been implicated in maintaining behavioral homeostasis essential for the survival of an individual. However, recent evidence suggests its more widespread roles in behavioral coordination, extending to the social domain. The neuronal and circuit mechanisms behind the LH processing of social information are unknown. Here, we show that the LH represents distinct reward variables for “self” and “other” and is causally involved in shaping socially motivated behavior. During a Pavlovian conditioning procedure incorporating ubiquitous social experiences where rewards to others affect one’s motivation, LH cells encoded the subjective value of self-rewards, as well as the likelihood of self- or other-rewards. The other-reward coding was not a general consequence of other’s existence, but a specific effect of other’s reward availability. Coherent activity with and top-down information flow from the medial prefrontal cortex, a hub of social brain networks, contributed to signal encoding in the LH. Furthermore, deactivation of LH cells eliminated the motivational impact of other-rewards. These results indicate that the LH constitutes a subcortical node in social brain networks and shapes one’s motivation by integrating cortically derived, agent-specific reward information.
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