Drop a mouse into a tiny enclosure, instruct it that nudging its nose into a lit opening results in a taste of sugar water, and soon enough the creature comes to anticipate the reward. Then remove the reward. Deep within its brain, in a cluster of tissue older than the cerebral cortex, a specific group of cells activates. Not due to something negative happening, precisely. Because a positive expectation did not materialize.<\/p>\n
These cells are the focus of recent research by a team at the University of Oregon, published last month in *Current Biology*. They detail a neuron population that functions, in a sense, like a gauge for disappointment, firing increasingly as reality deviates from what the animal had been conditioned to expect.<\/p>\n
The area of interest is the lateral habenula, a small, evolutionarily ancient structure nestled deep within the brain. It has been recognized by neuroscientists for years. Previous studies indicated it responds when something unpleasant unexpectedly occurs, or when a hoped-for reward fails to arrive, which is how it acquired its rather bleak moniker: the brain\u2019s **anti-reward center**. However, the habenula is a dense region, filled with various neuron types, and deciphering which cell performs which role has been a gradual process.<\/p>\n
\u201cWhat we aim to comprehend is how these different cell types correlate with specific behaviors,\u201d states Emily Sylwestrak, the assistant biology professor leading the study. \u201cThis new paper examines a cell type that we believe plays a distinctly specific role in the reward system.\u201d<\/p>\n
The cell type her team concentrated on is identified by a gene known as Tac1. Other researchers had recognized these cells previously, but no one had a straightforward method to monitor them specifically. Sylwestrak stumbled upon the challenge by chance. While examining a neighboring area, she continually detected stray signals from adjacent cells, signals that emerged in her recordings each time a mouse searched for a reward, investigated, and returned empty-handed.<\/p>\n
To effectively eavesdrop, the team modified mice so that the Tac1 cells would illuminate when active, then inserted a thin optical fiber into the habenula to capture the light. The mice performed the poke-for-sugar task, except now the reward was sometimes diminished and at times completely withheld.<\/p>\n
The cells remained quiet for most of the test. During the nose poke and approach, there was little activity. But the moment an anticipated reward fell short, they erupted into action, and (this is the ingenious part) the magnitude of that response correlated with how significantly the animal was let down. Decrease the reward and the cells fired slightly. Eliminate it fully and they fired intensely. The signal was so consistent that researchers could estimate how much sugar water a mouse had received simply by observing its neuronal activity.<\/p>\n
\u201cIt\u2019s akin to being able to capture your neuronal signals and determine whether you received one, two, or three Skittles when you expected five,\u201d remarks Sylwestrak. \u201cThe activity in these cells serves as a reliable indicator of the difference between expectation and reality, effectively acting as a disappointment meter.\u201d<\/p>\n
### Not all bad news is the same<\/p>\n
What elevates this finding from mere curiosity is what the cells did not respond to. When the mice experienced an unexpected burst of air, or brief confinement, or mild stimulation, the Tac1 cells barely reacted. They do not appear to be general bad-news detectors. Instead, they seem specifically responsive to one particular type of letdown: the disparity between an anticipated reward and a disappointing outcome. It becomes evident that unpleasant surprises are not all uniform.<\/p>\n
This specificity holds more significance than it may appear. \u201cWe don\u2019t necessarily want to evaluate or interpret all negative outcomes in the same manner, as you can envision that various negative experiences necessitate different behavioral responses,\u201d explains Kana Suzuki, the doctoral student who led the study. A concealed snake and a vending machine that swallowed your coin both represent negative experiences, yet they invoke vastly different reactions, and the brain seems to recognize this.<\/p>\n
Underlying all this is a concept in neuroscience known as reward prediction error: the continual record your brain maintains regarding how well its predictions align with what actually transpires. Receiving more than anticipated results in a positive error. Receiving less results in a negative one. The Tac1 cells specialize in the negative variant, and they seem to perform their calculations on a remarkably quick turnaround, updating on a per-trial basis. A series of recent disappointments diminished the response to the subsequent one, as if the brain were subtly lowering its expectations. \u201cYou inevitably resort to your history of successes and failures the next time you must make a decision or choose differently,\u201d says Suzuki.<\/p>\n
### From eavesdropping to meddling<\/p>\n
There are limitations, of course. This research is conducted in mice, and the transition from a sugar port to the complexities of human mood is substantial.<\/p>\n","protected":false},"excerpt":{"rendered":"
Drop a mouse into a tiny enclosure, instruct it that nudging its nose into a lit opening results in a taste of sugar water, and soon enough the creature comes to anticipate the reward. Then remove the reward. Deep within its brain, in a cluster of tissue older than the cerebral cortex, a specific group […]<\/p>\n","protected":false},"author":1,"featured_media":372864,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"Default","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[179],"class_list":["post-372863","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized","tag-source-scienceblog-com"],"_links":{"self":[{"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/posts\/372863","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=372863"}],"version-history":[{"count":0,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/posts\/372863\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/media\/372864"}],"wp:attachment":[{"href":"https:\/\/wolfscientific.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=372863"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=372863"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=372863"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}