{"id":218910,"date":"2024-10-11T00:00:27","date_gmt":"2024-10-11T04:00:27","guid":{"rendered":"https:\/\/www.thetransmitter.org\/?p=218910"},"modified":"2024-10-11T11:40:30","modified_gmt":"2024-10-11T15:40:30","slug":"should-i-stay-and-eat-or-should-i-go-how-the-brain-balances-hunger-with-competing-drives","status":"publish","type":"post","link":"https:\/\/www.thetransmitter.org\/internal-state\/should-i-stay-and-eat-or-should-i-go-how-the-brain-balances-hunger-with-competing-drives\/","title":{"rendered":"Should I stay (and eat) or should I go? How the brain balances hunger with competing drives"},"content":{"rendered":"","protected":false},"excerpt":{"rendered":"

Understanding the interplay among rival signals, such as pain, thirst and fear, could provide insights into anxiety and other neuropsychiatric conditions.<\/p>\n","protected":false},"author":2,"featured_media":218912,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_relevanssi_hide_post":"","_relevanssi_hide_content":"","_relevanssi_pin_for_all":"","_relevanssi_pin_keywords":"","_relevanssi_unpin_keywords":"","_relevanssi_related_keywords":"","_relevanssi_related_include_ids":"","_relevanssi_related_exclude_ids":"","_relevanssi_related_no_append":"","_relevanssi_related_not_related":"","_relevanssi_related_posts":"","_relevanssi_noindex_reason":""},"categories":[152],"tags":[83,226,296,308,610,167],"acf":{"primary_tag":308,"doi_url":"https:\/\/doi.org\/10.53053\/LMSO3428","custom_js_library":"","hero_type":"feat_image","hero_alt_image":null,"hero_youtube":"","hero_video":null,"hero_layout":"full","hero_caption":"Need to feed:<\/strong> New clues about where and how hunger collides with rival motivations, such as thirst, have come from technology to manipulate and monitor individual neurons across multiple brain regions at once.","hero_by":"Illustration by","hero_credit":205252,"hero_bg_color":"none","authors":[107386],"other_authors":"","related_title":"Explore more from The Transmitter<\/em>","related_hide":false,"related_filter":"latest","related_tag":null,"related_category":null,"related_custom":{"articles":null},"recommended_title":"Recommended reading","recommended_hide":false,"recommended_filter":"latest","recommended_tag":null,"recommended_category":null,"recommended_custom":{"articles":null},"comps":[{"acf_fc_layout":"copy_comp","copy":"As the famed tale \u201cHansel and Gretel\u201d makes clear, hunger can change behavior. The two lost and starving siblings give in to the temptation of a gingerbread cottage and ignore the danger lurking within\u2014a wicked witch who has created the delicious house as a trap.\r\n\r\nHunger is such a powerful driver that animals often pursue food at the expense of other survival needs, such as avoiding predators or recovering from injury. Hungry vicu\u00f1as, for example, will sometimes increase their risk of predation by pumas to get something to eat, behavioral ecologists have shown<\/a>.\r\n\r\nScientists know many of the key cells and circuits behind these competing drives\u2014such as the hypothalamic \u201chunger neurons\u201d that regulate food intake. But how the brain juggles the need to eat amidst other urges has remained mysterious, says Henning Fenselau<\/a>, who leads the Synaptic Transmission in Energy Homeostasis group at the Max Planck Institute for Metabolism Research in K\u00f6ln, Germany. \u201cThis is still a huge question [in neuroscience],\u201d he says.\r\n\r\nIn recent years, however, new clues about where and how hunger collides with rival motivations have come from technology to manipulate and monitor individual neurons across multiple brain regions at once. Those findings suggest that hunger neuron activity can override some brain signals, such as fear and pain.\r\n\r\nExploring the brain\u2019s ability to handle multiple needs simultaneously may offer insights into decision-making, anxiety and other neuropsychiatric conditions\u2014helping to explain why people sometimes make maladaptive choices, says Nicholas Betley<\/a>, associate professor of biology at the University of Pennsylvania.\r\n\r\n\u201cNeuroscience has been running with the hypothesis that the brain is built to focus attention on the most important task at a given time,\u201d he says. \u201cIt\u2019s not that we\u2019re going to necessarily disprove that, but I think the brain is probably capable of doing more than one thing.\u201d\r\n\r\n[tt_text class='']P[\/tt_text]art of the challenge in understanding hunger is that it has no single locus in the brain, although cells in the arcuate nucleus play an outsized role in sensing the body\u2019s energy stores and communicating that information to the rest of the brain. These hunger neurons, which express agouti-related peptide (AgRP), typically show low activity when an animal is sated but spring into action during periods of food deprivation or prolonged physical activity.\r\n\r\nEven in fed mice, though, activating these neurons drives food intake, according to a 2016 study<\/a>, and sometimes supersedes social needs, fear and thirst. But not always. Mice that are both hungry and thirsty alternate between choosing food or drink, a study<\/a> published in November 2023 shows. This switching back and forth ensures that over time, the mice meet both needs and aren\u2019t trapped in indecision, says lead investigator Liqun Luo<\/a>, professor of biology at Stanford University.\r\n\r\nThe animal\u2019s selections were not unpredictable, however: Neuronal activity patterns throughout the brain predicted a mouse\u2019s choice\u2014before it was even presented with options. This suggests that choices may depend on the brain\u2019s state before decision-making begins, says Ethan Richman<\/a>, a graduate student in Luo\u2019s lab.\r\n\r\n[tt_sidebar_quote author='Nicholas Betley']When you activate [hunger] neurons to their maximum threshold, the animals do some pretty amazing things\u2014they will overcome a lot of fear.[\/tt_sidebar_quote]\r\n\r\nTo explain their findings, Richman and his colleagues turned to mathematical modeling. Their model\u2014in which the mouse\u2019s brain activity fluctuates randomly, helping it transition between hunger and thirst\u2014accurately predicted aspects of mouse behavior. It also indicated that the brain is often \u201ctrapped\u201d by different needs, switching from one to another as a result of random bursts of neuronal activity.\r\n\r\n\u201cEven though we use thirst and hunger to probe how brain states influence behavior,\u201d Luo says, \u201cwe think that this kind of conceptual framework can be applied to other brain states.\u201d\r\n\r\nThis kind of predictive modeling approach is \u201cthe dream,\u201d Betley says. \u201cWhat are the things that are going to put you into a negative state, and how would one be able to get out of that?\u201d But Luo\u2019s model doesn\u2019t account for other factors that could influence decision making around hunger, such as immediate threats or pain, he adds.\r\n\r\nAcute pain, for example, but not chronic pain, can suppress appetite and hunger neuron activity<\/a> in mice, Betley and his team showed in 2018. On the other hand, hunger can override chronic but not acute pain, the work also showed: Hungry mice spent less time than controls did licking an inflamed paw injected with a chemical, and this response was linked to increased activity among AgRP-expressing hunger neurons. But going without food did not change the animals\u2019 reaction to short-lived pain caused by heat or pressure.\r\n\r\n\u201cIf an animal has an injury that takes months to heal, it can\u2019t just stay in its nest\u2014it must get out. There\u2019s a filtering process that happens here,\u201d Betley says.\r\n\r\nThe prevailing theory is that filtering out certain brain signals serves to prioritize other needs, he adds, but this filtering may not be beneficial, for example, when a predator is nearby. \u201cWe\u2019re trying to figure out in the lab how that balance is mediated, and how the neural networks encode either the filtering or the weighing of the decision.\u201d\r\n\r\nActivating a group of about 300 hunger neurons that project into the parabrachial nucleus, a brain region that processes sensory information related to pain, could almost completely stop chronic pain, the researchers found.\r\n\r\nBy contrast, hunger signals don\u2019t seem to directly suppress fear, Betley\u2019s team also found, even though hunger neurons communicate with brain areas that process fear, such as the amygdala. \u201cWe\u2019re not finding a discrete location where hunger and fear collide,\u201d he says. \u201cThat doesn\u2019t mean it doesn\u2019t exist, but the fact that we haven\u2019t found it yet suggests that maybe we\u2019re not looking at the simplest filter here.\u201d\r\n\r\n[tt_text class='']T[\/tt_text]here may be a critical threshold at which hunger overtakes fear, according to unpublished results Betley presented in June at the FENS Forum in Vienna. In that work, a mouse exposed to a predator\u2019s scent prioritized seeking food only when the team artificially activated a significant number of its hunger neurons\u2014although the exact number varied between animals.\r\n\r\n\u201cWhen you activate [hunger] neurons to their maximum threshold, the animals do some pretty amazing things\u2014they will overcome a lot of fear,\u201d Betley says. For example, mice will approach a rat predator to get food, a study<\/a> published last year showed.\r\n\r\nBetley\u2019s work may help advance our understanding of how the brain manages competition between different drives, Fenselau says.\r\n\r\nFenselau and his team added to this emerging picture in June, showing that activated AgRP neurons simultaneously strengthen hunger signals and weaken anxiety signals in the bed nucleus of the stria terminalis\u2014a brain structure that integrates various inputs to regulate emotional responses. This adaptation may make it possible for mice to prioritize hunger over fear, even in risky situations.\r\n\r\nThe results also indicate that AgRP neurons produce a neurotransmitter called neuropeptide Y that modulates synaptic transmission in a targeted way: \u201cWhen an animal is very hungry, the input from AgRP neurons becomes strengthened, whereas the signaling from the anxiety inputs from the central amygdala becomes much more weakened,\u201d Fenselau says.\r\n\r\nThe mechanisms by which neuropeptide Y functions and travels between synapses remain unknown, he adds. \u201cWe are still at the beginning of [understanding] how complex the brain is, and how this neuropeptide works.\u201d\r\n\r\nFor his part, Betley now plans to look at calcium dynamics in the entire cortex of awake mice to investigate how the region processes hunger and fear signals to make decisions such as eating or fleeing. By comparing brain activity when animals are sated versus hungry and exposed to various stimuli\u2014as well as recording the animals\u2019 facial expressions and stress hormones\u2014he says he hopes to further decode how hunger and fear affect decision-making.\r\n\r\nBetley says he suspects that an animal\u2019s hunger circuits do not filter out an acute threat. But in the presence of a latent threat\u2014for example, the residual scent of a predator\u2014hunger may prevail over fear. Because an individual animal\u2019s life history influences drives such as hunger and thirst, the brain\u2019s ability to filter a latent threat is likely adaptive, particularly as the animal\u2019s state changes, he says.\r\n\r\n\u201cYour life history may predict a resting brain state that\u2019s different from mine,\u201d he says. \u201cIt\u2019s important for [neuroscientists] to consider the fact that none of these things happen in isolation.\u201d\r\n\r\nWith additional reporting by Angie Voyles Askham.<\/em>"},{"acf_fc_layout":"newsletter","title":"Sign up for our weekly newsletter.","subtitle":" Catch up on what you may have missed from our recent coverage.","bg_image":200913,"groups":[{"group":"4","name":"","hide_checkbox":true}],"linktext":"","linkurl":""}]},"_links":{"self":[{"href":"https:\/\/www.thetransmitter.org\/wp-json\/wp\/v2\/posts\/218910"}],"collection":[{"href":"https:\/\/www.thetransmitter.org\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.thetransmitter.org\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.thetransmitter.org\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.thetransmitter.org\/wp-json\/wp\/v2\/comments?post=218910"}],"version-history":[{"count":4,"href":"https:\/\/www.thetransmitter.org\/wp-json\/wp\/v2\/posts\/218910\/revisions"}],"predecessor-version":[{"id":218976,"href":"https:\/\/www.thetransmitter.org\/wp-json\/wp\/v2\/posts\/218910\/revisions\/218976"}],"acf:post":[{"embeddable":true,"href":"https:\/\/www.thetransmitter.org\/wp-json\/wp\/v2\/contributor\/107386"},{"embeddable":true,"href":"https:\/\/www.thetransmitter.org\/wp-json\/wp\/v2\/contributor\/205252"}],"acf:term":[{"embeddable":true,"taxonomy":"post_tag","href":"https:\/\/www.thetransmitter.org\/wp-json\/wp\/v2\/tags\/308"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.thetransmitter.org\/wp-json\/wp\/v2\/media\/218912"}],"wp:attachment":[{"href":"https:\/\/www.thetransmitter.org\/wp-json\/wp\/v2\/media?parent=218910"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.thetransmitter.org\/wp-json\/wp\/v2\/categories?post=218910"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.thetransmitter.org\/wp-json\/wp\/v2\/tags?post=218910"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}