{"id":197,"date":"2023-02-17T22:37:18","date_gmt":"2023-02-17T22:37:18","guid":{"rendered":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/chapter\/3-2-apply-it\/"},"modified":"2026-02-03T17:40:30","modified_gmt":"2026-02-03T17:40:30","slug":"3-2-apply-it","status":"publish","type":"chapter","link":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/chapter\/3-2-apply-it\/","title":{"raw":"The Peripheral Nervous System and the Endocrine System: Apply It","rendered":"The Peripheral Nervous System and the Endocrine System: Apply It"},"content":{"raw":"<section class=\"textbox learningGoals\">\r\n<ul>\r\n\t<li>Describe the differences between the central and peripheral nervous systems and the somatic and autonomic nervous systems<\/li>\r\n\t<li>Describe the difference between the sympathetic and parasympathetic divisions of the autonomic nervous system<\/li>\r\n\t<li><span data-sheets-value=\"{&quot;1&quot;:2,&quot;2&quot;:&quot;Describe the endocrine system and how it affects behavior&quot;}\" data-sheets-userformat=\"{&quot;2&quot;:12673,&quot;3&quot;:{&quot;1&quot;:0},&quot;10&quot;:2,&quot;11&quot;:4,&quot;15&quot;:&quot;Calibri&quot;,&quot;16&quot;:9}\">Describe the endocrine system and how it affects behavior<\/span><\/li>\r\n<\/ul>\r\n<\/section>\r\n<section class=\"textbox interact\" aria-label=\"Interact\">\r\n<p>First, review some key components of the endocrine system by matching the words with their definitions.<\/p>\r\n<p><iframe src=\"https:\/\/lumenlearning.h5p.com\/content\/1291880103496990308\/embed\" width=\"1089\" height=\"651\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\" aria-label=\"(3. Endocrine System) Vocab Drag and Drop\"><\/iframe><script src=\"https:\/\/lumenlearning.h5p.com\/js\/h5p-resizer.js\" charset=\"UTF-8\"><\/script><\/p>\r\n<\/section>\r\n<section class=\"textbox tryIt\">[ohm2_question height=\"850\"]3955[\/ohm2_question]<\/section>\r\n<section class=\"textbox connectIt\" aria-label=\"Connect It\">\r\n<h3>Beyond Neurons and Hormones: The Gut\u2013Brain Axis<\/h3>\r\n<p>The nervous and endocrine systems keep your body balanced, but researchers have uncovered another network that connects the brain and body\u2014the <strong>gut\u2013brain axis<\/strong>.<\/p>\r\n<p>This system links the <strong>digestive tract<\/strong>, <strong>immune system<\/strong>, and <strong>central nervous system<\/strong> through a constant exchange of chemical and neural messages. The gut doesn't just digest food; it also produces hormones, neurotransmitters, and immune molecules that can affect <strong>mood<\/strong>, <strong>stress<\/strong>, and <strong>thinking<\/strong>. What happens in the gut can influence the mind\u2014and vice versa.<\/p>\r\n<h4>What Is the Gut\u2013Brain Axis?<\/h4>\r\n<p>The gut\u2013brain axis is a <strong>two-way communication system<\/strong> between the <strong>brain<\/strong> and the <strong>digestive tract<\/strong>. The brain can influence digestion and stress responses, while the <strong>gut microbiota<\/strong>\u2014the trillions of microorganisms living in your intestines\u2014can affect brain chemistry and behavior through <strong>immune<\/strong>, <strong>hormonal<\/strong>, and <strong>neural<\/strong> pathways (Doenyas, Clarke, &amp; Cserj\u00e9si, 2025).[footnote]Doenyas, C., Clarke, G., &amp; Cserj\u00e9si, R. (2025). Gut\u2013brain axis and neuropsychiatric health: Recent advances. <em>Scientific Reports, 15<\/em>, 3415. https:\/\/doi.org\/10.1038\/s41598-025-86858-3[\/footnote]<\/p>\r\n<p>Your gut hosts more than <strong>1,000 bacterial species<\/strong>, dominated by <em>Firmicutes<\/em> and <em>Bacteroidetes<\/em>, with smaller groups like <em>Actinobacteria<\/em> and <em>Proteobacteria<\/em> (Vl\u0103du\u021bu et al., 2025).[footnote]Vl\u0103du\u021bu, D. S., et al. (2025). Gut over mind: Exploring the powerful gut\u2013brain axis. <em>Nutrients, 17<\/em>(5), 842. https:\/\/doi.org\/10.3390\/nu17050842[\/footnote] Because it contains the body's <strong>second-largest cluster of neurons<\/strong> after the brain, scientists call it the <strong>\"second brain.\"<\/strong><\/p>\r\n<h4>How Do the Gut and Brain Communicate?<\/h4>\r\n<ul>\r\n\t<li><strong>Neural Pathways:<\/strong> The <strong>vagus nerve<\/strong> acts as a communication highway, carrying signals in both directions\u2014allowing the brain to regulate digestion and the gut to report on what's happening inside the intestines.<\/li>\r\n\t<li><strong>Immune System Interactions:<\/strong> Gut bacteria produce metabolites that influence immune responses, which can affect brain activity and mood (Wang, Buffington, &amp; Salas, 2024).[footnote]Wang, I. C., Buffington, S. A., &amp; Salas, R. (2024). Microbiota\u2013gut\u2013brain axis in psychiatry: Focus on depressive disorders. <em>Current Opinion in Behavioral Sciences, 11<\/em>(4), 222\u2013232.[\/footnote] When this balance is disrupted\u2014a condition called <strong>dysbiosis<\/strong>\u2014inflammation may rise and contribute to anxiety or depression.<\/li>\r\n\t<li><strong>Neuroendocrine Signaling:<\/strong> The <strong>hypothalamic\u2013pituitary\u2013adrenal (HPA) axis<\/strong> coordinates the body's stress response. Stress hormones such as <strong>cortisol<\/strong> can change the gut's microbial composition, while some microbes can influence HPA activity, creating a <strong>feedback loop<\/strong> between stress and digestion (Kim &amp; Shin, 2018).[footnote]Kim, Y. K., &amp; Shin, C. (2018). The microbiota\u2013gut\u2013brain axis in neuropsychiatric disorders: Pathophysiological mechanisms and novel treatments. <em>Current Neuropharmacology, 16<\/em>(5), 559\u2013573.[\/footnote]<\/li>\r\n\t<li><strong>Neurotransmitter Production:<\/strong> Many gut bacteria help make <strong>neurotransmitters<\/strong> such as serotonin, dopamine, and GABA. Remarkably, about <strong>90 percent of the body's serotonin<\/strong> is produced in the gut, not the brain (Yano et al., 2015).[footnote]Yano, J. M., Yu, K., Donaldson, G. P., et al. (2015). Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis. <em>Cell, 161<\/em>(2), 264\u2013276. https:\/\/doi.org\/10.1016\/j.cell.2015.02.047[\/footnote] However, this gut-produced serotonin cannot cross the <strong>blood\u2013brain barrier<\/strong>, a protective layer that blocks most substances from entering the brain. Instead, it influences brain function indirectly by stimulating the vagus nerve and affecting stress-hormone signaling (Cain, 2023).[footnote]Cain, N. (2023). Depression, serotonin, and the gut. <em>Psychology Today<\/em>. https:\/\/www.psychologytoday.com\/us\/blog\/mood-mind-and-microbes\/202304\/depression-serotonin-and-the-gut[\/footnote]<\/li>\r\n\t<li><strong>Short-Chain Fatty Acids:<\/strong> Gut microbes also generate <strong>short-chain fatty acids (SCFAs)<\/strong>\u2014small molecules formed when bacteria digest dietary fiber\u2014that can cross the blood\u2013brain barrier and directly affect brain function. SCFAs such as <strong>butyrate<\/strong> help maintain barrier integrity and support mood regulation (Flora, 2024; van de Wouw et al., 2018). People with depression often have <strong>lower SCFA levels<\/strong> and reduced microbial diversity (Liu et al., 2020).[footnote]Liu, S., Guo, R., Liu, F., et al. (2020). Associations between disordered gut microbiota and changes of neurotransmitters and short-chain fatty acids in depressed mice. <em>Translational Psychiatry, 10<\/em>, 350. https:\/\/doi.org\/10.1038\/s41398-020-01038-3[\/footnote]<\/li>\r\n<\/ul>\r\n<h4>Emerging Research on the Gut\u2013Brain Axis and Mental Health<\/h4>\r\n<ul>\r\n\t<li><strong>Depression and Anxiety:<\/strong> Individuals with depression often show less diverse microbiomes and shifts in bacterial composition compared with healthy individuals, changes that may influence immune and metabolic processes tied to mood (Pan et al., 2025).[footnote]Pan, B., Pan, Y., Huang, Y. S., et al. (2025). Efficacy and safety of gut microbiome-targeted treatment in patients with depression: A systematic review and meta-analysis. <em>BMC Psychiatry, 25<\/em>, 64. https:\/\/doi.org\/10.1186\/s12888-024-06438-z[\/footnote]<\/li>\r\n\t<li><strong>Stress Response:<\/strong> Chronic stress activates the HPA axis and disrupts gut bacteria, increasing gut permeability and inflammation. This disturbance may intensify anxiety and reinforce a brain\u2013gut feedback loop (Doenyas et al., 2025).<\/li>\r\n\t<li><strong>Social Behavior and Personality:<\/strong> People with larger social networks tend to have more diverse gut microbes, suggesting that social interaction itself may shape the gut microbiome (Johnson, 2020).[footnote]Johnson, K. (2020). Gut microbiome composition and diversity are related to human personality traits. <em>Human Microbiome Journal, 15<\/em>, 100069.[\/footnote]<\/li>\r\n<\/ul>\r\n<h4>Therapeutic Implications<\/h4>\r\n<ul>\r\n\t<li><strong>Psychobiotics:<\/strong> These probiotic supplements aim to support mental health. Meta-analyses show that certain strains\u2014such as <em>Lactobacillus plantarum<\/em> PS128 and <em>Bifidobacterium breve<\/em>\u2014can modestly reduce depression and anxiety, though effects are small and vary by strain (Pan et al., 2025).<\/li>\r\n\t<li><strong>Dietary Interventions:<\/strong> <strong>High-fiber, plant-rich diets<\/strong>\u2014like the Mediterranean diet\u2014promote microbial diversity, lower inflammation, and correlate with improved mood (Vl\u0103du\u021bu et al., 2025).<\/li>\r\n\t<li><strong>Fecal Microbiota Transplantation (FMT):<\/strong> FMT transfers gut microbes from a healthy donor to a patient's intestines. Early trials show possible mood benefits, but this approach remains <strong>experimental<\/strong> for mental-health treatment (Vl\u0103du\u021bu et al., 2025).<\/li>\r\n<\/ul>\r\n<h4>Current Research and Future Directions<\/h4>\r\n<p>Scientists continue to study how the microbiome interacts with the brain in neurodegenerative, psychiatric, and metabolic disorders\u2014from Parkinson's disease to mood disorders (Doenyas et al., 2025). These insights may lead to microbiome-based therapies that complement existing psychological and medical approaches.<\/p>\r\n<p>The gut\u2013brain axis demonstrates a core biopsychological principle: the mind and body are interconnected. Mental health depends not only on brain activity but also on the ecosystems within our bodies\u2014ecosystems shaped by diet, stress, sleep, and lifestyle.<\/p>\r\n<\/section>\r\n<section class=\"textbox tryIt\" aria-label=\"Try It\">[ohm2_question]42283[\/ohm2_question]<\/section>","rendered":"<section class=\"textbox learningGoals\">\n<ul>\n<li>Describe the differences between the central and peripheral nervous systems and the somatic and autonomic nervous systems<\/li>\n<li>Describe the difference between the sympathetic and parasympathetic divisions of the autonomic nervous system<\/li>\n<li><span data-sheets-value=\"{&quot;1&quot;:2,&quot;2&quot;:&quot;Describe the endocrine system and how it affects behavior&quot;}\" data-sheets-userformat=\"{&quot;2&quot;:12673,&quot;3&quot;:{&quot;1&quot;:0},&quot;10&quot;:2,&quot;11&quot;:4,&quot;15&quot;:&quot;Calibri&quot;,&quot;16&quot;:9}\">Describe the endocrine system and how it affects behavior<\/span><\/li>\n<\/ul>\n<\/section>\n<section class=\"textbox interact\" aria-label=\"Interact\">\n<p>First, review some key components of the endocrine system by matching the words with their definitions.<\/p>\n<p><iframe loading=\"lazy\" src=\"https:\/\/lumenlearning.h5p.com\/content\/1291880103496990308\/embed\" width=\"1089\" height=\"651\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\" aria-label=\"(3. Endocrine System) Vocab Drag and Drop\"><\/iframe><script src=\"https:\/\/lumenlearning.h5p.com\/js\/h5p-resizer.js\" charset=\"UTF-8\"><\/script><\/p>\n<\/section>\n<section class=\"textbox tryIt\"><iframe loading=\"lazy\" id=\"ohm3955\" class=\"resizable\" src=\"https:\/\/ohm.one.lumenlearning.com\/multiembedq.php?id=3955&theme=lumen&iframe_resize_id=ohm3955&source=tnh&show_question_numbers\" width=\"100%\" height=\"850\"><\/iframe><\/section>\n<section class=\"textbox connectIt\" aria-label=\"Connect It\">\n<h3>Beyond Neurons and Hormones: The Gut\u2013Brain Axis<\/h3>\n<p>The nervous and endocrine systems keep your body balanced, but researchers have uncovered another network that connects the brain and body\u2014the <strong>gut\u2013brain axis<\/strong>.<\/p>\n<p>This system links the <strong>digestive tract<\/strong>, <strong>immune system<\/strong>, and <strong>central nervous system<\/strong> through a constant exchange of chemical and neural messages. The gut doesn&#8217;t just digest food; it also produces hormones, neurotransmitters, and immune molecules that can affect <strong>mood<\/strong>, <strong>stress<\/strong>, and <strong>thinking<\/strong>. What happens in the gut can influence the mind\u2014and vice versa.<\/p>\n<h4>What Is the Gut\u2013Brain Axis?<\/h4>\n<p>The gut\u2013brain axis is a <strong>two-way communication system<\/strong> between the <strong>brain<\/strong> and the <strong>digestive tract<\/strong>. The brain can influence digestion and stress responses, while the <strong>gut microbiota<\/strong>\u2014the trillions of microorganisms living in your intestines\u2014can affect brain chemistry and behavior through <strong>immune<\/strong>, <strong>hormonal<\/strong>, and <strong>neural<\/strong> pathways (Doenyas, Clarke, &amp; Cserj\u00e9si, 2025).<a class=\"footnote\" title=\"Doenyas, C., Clarke, G., &amp; Cserj\u00e9si, R. (2025). Gut\u2013brain axis and neuropsychiatric health: Recent advances. Scientific Reports, 15, 3415. https:\/\/doi.org\/10.1038\/s41598-025-86858-3\" id=\"return-footnote-197-1\" href=\"#footnote-197-1\" aria-label=\"Footnote 1\"><sup class=\"footnote\">[1]<\/sup><\/a><\/p>\n<p>Your gut hosts more than <strong>1,000 bacterial species<\/strong>, dominated by <em>Firmicutes<\/em> and <em>Bacteroidetes<\/em>, with smaller groups like <em>Actinobacteria<\/em> and <em>Proteobacteria<\/em> (Vl\u0103du\u021bu et al., 2025).<a class=\"footnote\" title=\"Vl\u0103du\u021bu, D. S., et al. (2025). Gut over mind: Exploring the powerful gut\u2013brain axis. Nutrients, 17(5), 842. https:\/\/doi.org\/10.3390\/nu17050842\" id=\"return-footnote-197-2\" href=\"#footnote-197-2\" aria-label=\"Footnote 2\"><sup class=\"footnote\">[2]<\/sup><\/a> Because it contains the body&#8217;s <strong>second-largest cluster of neurons<\/strong> after the brain, scientists call it the <strong>&#8220;second brain.&#8221;<\/strong><\/p>\n<h4>How Do the Gut and Brain Communicate?<\/h4>\n<ul>\n<li><strong>Neural Pathways:<\/strong> The <strong>vagus nerve<\/strong> acts as a communication highway, carrying signals in both directions\u2014allowing the brain to regulate digestion and the gut to report on what&#8217;s happening inside the intestines.<\/li>\n<li><strong>Immune System Interactions:<\/strong> Gut bacteria produce metabolites that influence immune responses, which can affect brain activity and mood (Wang, Buffington, &amp; Salas, 2024).<a class=\"footnote\" title=\"Wang, I. C., Buffington, S. A., &amp; Salas, R. (2024). Microbiota\u2013gut\u2013brain axis in psychiatry: Focus on depressive disorders. Current Opinion in Behavioral Sciences, 11(4), 222\u2013232.\" id=\"return-footnote-197-3\" href=\"#footnote-197-3\" aria-label=\"Footnote 3\"><sup class=\"footnote\">[3]<\/sup><\/a> When this balance is disrupted\u2014a condition called <strong>dysbiosis<\/strong>\u2014inflammation may rise and contribute to anxiety or depression.<\/li>\n<li><strong>Neuroendocrine Signaling:<\/strong> The <strong>hypothalamic\u2013pituitary\u2013adrenal (HPA) axis<\/strong> coordinates the body&#8217;s stress response. Stress hormones such as <strong>cortisol<\/strong> can change the gut&#8217;s microbial composition, while some microbes can influence HPA activity, creating a <strong>feedback loop<\/strong> between stress and digestion (Kim &amp; Shin, 2018).<a class=\"footnote\" title=\"Kim, Y. K., &amp; Shin, C. (2018). The microbiota\u2013gut\u2013brain axis in neuropsychiatric disorders: Pathophysiological mechanisms and novel treatments. Current Neuropharmacology, 16(5), 559\u2013573.\" id=\"return-footnote-197-4\" href=\"#footnote-197-4\" aria-label=\"Footnote 4\"><sup class=\"footnote\">[4]<\/sup><\/a><\/li>\n<li><strong>Neurotransmitter Production:<\/strong> Many gut bacteria help make <strong>neurotransmitters<\/strong> such as serotonin, dopamine, and GABA. Remarkably, about <strong>90 percent of the body&#8217;s serotonin<\/strong> is produced in the gut, not the brain (Yano et al., 2015).<a class=\"footnote\" title=\"Yano, J. M., Yu, K., Donaldson, G. P., et al. (2015). Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis. Cell, 161(2), 264\u2013276. https:\/\/doi.org\/10.1016\/j.cell.2015.02.047\" id=\"return-footnote-197-5\" href=\"#footnote-197-5\" aria-label=\"Footnote 5\"><sup class=\"footnote\">[5]<\/sup><\/a> However, this gut-produced serotonin cannot cross the <strong>blood\u2013brain barrier<\/strong>, a protective layer that blocks most substances from entering the brain. Instead, it influences brain function indirectly by stimulating the vagus nerve and affecting stress-hormone signaling (Cain, 2023).<a class=\"footnote\" title=\"Cain, N. (2023). Depression, serotonin, and the gut. Psychology Today. https:\/\/www.psychologytoday.com\/us\/blog\/mood-mind-and-microbes\/202304\/depression-serotonin-and-the-gut\" id=\"return-footnote-197-6\" href=\"#footnote-197-6\" aria-label=\"Footnote 6\"><sup class=\"footnote\">[6]<\/sup><\/a><\/li>\n<li><strong>Short-Chain Fatty Acids:<\/strong> Gut microbes also generate <strong>short-chain fatty acids (SCFAs)<\/strong>\u2014small molecules formed when bacteria digest dietary fiber\u2014that can cross the blood\u2013brain barrier and directly affect brain function. SCFAs such as <strong>butyrate<\/strong> help maintain barrier integrity and support mood regulation (Flora, 2024; van de Wouw et al., 2018). People with depression often have <strong>lower SCFA levels<\/strong> and reduced microbial diversity (Liu et al., 2020).<a class=\"footnote\" title=\"Liu, S., Guo, R., Liu, F., et al. (2020). Associations between disordered gut microbiota and changes of neurotransmitters and short-chain fatty acids in depressed mice. Translational Psychiatry, 10, 350. https:\/\/doi.org\/10.1038\/s41398-020-01038-3\" id=\"return-footnote-197-7\" href=\"#footnote-197-7\" aria-label=\"Footnote 7\"><sup class=\"footnote\">[7]<\/sup><\/a><\/li>\n<\/ul>\n<h4>Emerging Research on the Gut\u2013Brain Axis and Mental Health<\/h4>\n<ul>\n<li><strong>Depression and Anxiety:<\/strong> Individuals with depression often show less diverse microbiomes and shifts in bacterial composition compared with healthy individuals, changes that may influence immune and metabolic processes tied to mood (Pan et al., 2025).<a class=\"footnote\" title=\"Pan, B., Pan, Y., Huang, Y. S., et al. (2025). Efficacy and safety of gut microbiome-targeted treatment in patients with depression: A systematic review and meta-analysis. BMC Psychiatry, 25, 64. https:\/\/doi.org\/10.1186\/s12888-024-06438-z\" id=\"return-footnote-197-8\" href=\"#footnote-197-8\" aria-label=\"Footnote 8\"><sup class=\"footnote\">[8]<\/sup><\/a><\/li>\n<li><strong>Stress Response:<\/strong> Chronic stress activates the HPA axis and disrupts gut bacteria, increasing gut permeability and inflammation. This disturbance may intensify anxiety and reinforce a brain\u2013gut feedback loop (Doenyas et al., 2025).<\/li>\n<li><strong>Social Behavior and Personality:<\/strong> People with larger social networks tend to have more diverse gut microbes, suggesting that social interaction itself may shape the gut microbiome (Johnson, 2020).<a class=\"footnote\" title=\"Johnson, K. (2020). Gut microbiome composition and diversity are related to human personality traits. Human Microbiome Journal, 15, 100069.\" id=\"return-footnote-197-9\" href=\"#footnote-197-9\" aria-label=\"Footnote 9\"><sup class=\"footnote\">[9]<\/sup><\/a><\/li>\n<\/ul>\n<h4>Therapeutic Implications<\/h4>\n<ul>\n<li><strong>Psychobiotics:<\/strong> These probiotic supplements aim to support mental health. Meta-analyses show that certain strains\u2014such as <em>Lactobacillus plantarum<\/em> PS128 and <em>Bifidobacterium breve<\/em>\u2014can modestly reduce depression and anxiety, though effects are small and vary by strain (Pan et al., 2025).<\/li>\n<li><strong>Dietary Interventions:<\/strong> <strong>High-fiber, plant-rich diets<\/strong>\u2014like the Mediterranean diet\u2014promote microbial diversity, lower inflammation, and correlate with improved mood (Vl\u0103du\u021bu et al., 2025).<\/li>\n<li><strong>Fecal Microbiota Transplantation (FMT):<\/strong> FMT transfers gut microbes from a healthy donor to a patient&#8217;s intestines. Early trials show possible mood benefits, but this approach remains <strong>experimental<\/strong> for mental-health treatment (Vl\u0103du\u021bu et al., 2025).<\/li>\n<\/ul>\n<h4>Current Research and Future Directions<\/h4>\n<p>Scientists continue to study how the microbiome interacts with the brain in neurodegenerative, psychiatric, and metabolic disorders\u2014from Parkinson&#8217;s disease to mood disorders (Doenyas et al., 2025). These insights may lead to microbiome-based therapies that complement existing psychological and medical approaches.<\/p>\n<p>The gut\u2013brain axis demonstrates a core biopsychological principle: the mind and body are interconnected. Mental health depends not only on brain activity but also on the ecosystems within our bodies\u2014ecosystems shaped by diet, stress, sleep, and lifestyle.<\/p>\n<\/section>\n<section class=\"textbox tryIt\" aria-label=\"Try It\"><iframe loading=\"lazy\" id=\"ohm42283\" class=\"resizable\" src=\"https:\/\/ohm.one.lumenlearning.com\/multiembedq.php?id=42283&theme=lumen&iframe_resize_id=ohm42283&source=tnh&show_question_numbers\" width=\"100%\" height=\"150\"><\/iframe><\/section>\n<hr class=\"before-footnotes clear\" \/><div class=\"footnotes\"><ol><li id=\"footnote-197-1\">Doenyas, C., Clarke, G., &amp; Cserj\u00e9si, R. (2025). Gut\u2013brain axis and neuropsychiatric health: Recent advances. <em>Scientific Reports, 15<\/em>, 3415. https:\/\/doi.org\/10.1038\/s41598-025-86858-3 <a href=\"#return-footnote-197-1\" class=\"return-footnote\" aria-label=\"Return to footnote 1\">&crarr;<\/a><\/li><li id=\"footnote-197-2\">Vl\u0103du\u021bu, D. S., et al. (2025). Gut over mind: Exploring the powerful gut\u2013brain axis. <em>Nutrients, 17<\/em>(5), 842. https:\/\/doi.org\/10.3390\/nu17050842 <a href=\"#return-footnote-197-2\" class=\"return-footnote\" aria-label=\"Return to footnote 2\">&crarr;<\/a><\/li><li id=\"footnote-197-3\">Wang, I. C., Buffington, S. A., &amp; Salas, R. (2024). Microbiota\u2013gut\u2013brain axis in psychiatry: Focus on depressive disorders. <em>Current Opinion in Behavioral Sciences, 11<\/em>(4), 222\u2013232. <a href=\"#return-footnote-197-3\" class=\"return-footnote\" aria-label=\"Return to footnote 3\">&crarr;<\/a><\/li><li id=\"footnote-197-4\">Kim, Y. K., &amp; Shin, C. (2018). The microbiota\u2013gut\u2013brain axis in neuropsychiatric disorders: Pathophysiological mechanisms and novel treatments. <em>Current Neuropharmacology, 16<\/em>(5), 559\u2013573. <a href=\"#return-footnote-197-4\" class=\"return-footnote\" aria-label=\"Return to footnote 4\">&crarr;<\/a><\/li><li id=\"footnote-197-5\">Yano, J. M., Yu, K., Donaldson, G. P., et al. (2015). Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis. <em>Cell, 161<\/em>(2), 264\u2013276. https:\/\/doi.org\/10.1016\/j.cell.2015.02.047 <a href=\"#return-footnote-197-5\" class=\"return-footnote\" aria-label=\"Return to footnote 5\">&crarr;<\/a><\/li><li id=\"footnote-197-6\">Cain, N. (2023). Depression, serotonin, and the gut. <em>Psychology Today<\/em>. https:\/\/www.psychologytoday.com\/us\/blog\/mood-mind-and-microbes\/202304\/depression-serotonin-and-the-gut <a href=\"#return-footnote-197-6\" class=\"return-footnote\" aria-label=\"Return to footnote 6\">&crarr;<\/a><\/li><li id=\"footnote-197-7\">Liu, S., Guo, R., Liu, F., et al. (2020). Associations between disordered gut microbiota and changes of neurotransmitters and short-chain fatty acids in depressed mice. <em>Translational Psychiatry, 10<\/em>, 350. https:\/\/doi.org\/10.1038\/s41398-020-01038-3 <a href=\"#return-footnote-197-7\" class=\"return-footnote\" aria-label=\"Return to footnote 7\">&crarr;<\/a><\/li><li id=\"footnote-197-8\">Pan, B., Pan, Y., Huang, Y. S., et al. (2025). Efficacy and safety of gut microbiome-targeted treatment in patients with depression: A systematic review and meta-analysis. <em>BMC Psychiatry, 25<\/em>, 64. https:\/\/doi.org\/10.1186\/s12888-024-06438-z <a href=\"#return-footnote-197-8\" class=\"return-footnote\" aria-label=\"Return to footnote 8\">&crarr;<\/a><\/li><li id=\"footnote-197-9\">Johnson, K. (2020). Gut microbiome composition and diversity are related to human personality traits. <em>Human Microbiome Journal, 15<\/em>, 100069. <a href=\"#return-footnote-197-9\" class=\"return-footnote\" aria-label=\"Return to footnote 9\">&crarr;<\/a><\/li><\/ol><\/div>","protected":false},"author":20,"menu_order":24,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"The Brain and Nervous System\",\"author\":\"Robert Biswas-Diener \",\"organization\":\"Portland State University\",\"url\":\"https:\/\/nobaproject.com\/modules\/the-brain-and-nervous-system\",\"project\":\"The Noba Project\",\"license\":\"cc-by-nc-sa\",\"license_terms\":\"\"},{\"type\":\"cc\",\"description\":\"The Brain and Spinal Cord\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"https:\/\/openstax.org\/books\/psychology-2e\/pages\/3-4-the-brain-and-spinal-cord\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Access for free at https:\/\/openstax.org\/books\/us-history\/pages\/1-introduction\"}]","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"part":210,"module-header":"apply_it","content_attributions":[{"type":"cc","description":"The Brain and Nervous System","author":"Robert Biswas-Diener ","organization":"Portland State University","url":"https:\/\/nobaproject.com\/modules\/the-brain-and-nervous-system","project":"The Noba Project","license":"cc-by-nc-sa","license_terms":""},{"type":"cc","description":"The Brain and Spinal Cord","author":"","organization":"OpenStax","url":"https:\/\/openstax.org\/books\/psychology-2e\/pages\/3-4-the-brain-and-spinal-cord","project":"","license":"cc-by","license_terms":"Access for free at https:\/\/openstax.org\/books\/us-history\/pages\/1-introduction"}],"internal_book_links":[],"video_content":null,"cc_video_embed_content":{"cc_scripts":"","media_targets":[]},"try_it_collection":null,"_links":{"self":[{"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/pressbooks\/v2\/chapters\/197"}],"collection":[{"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/wp\/v2\/users\/20"}],"version-history":[{"count":17,"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/pressbooks\/v2\/chapters\/197\/revisions"}],"predecessor-version":[{"id":7616,"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/pressbooks\/v2\/chapters\/197\/revisions\/7616"}],"part":[{"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/pressbooks\/v2\/parts\/210"}],"metadata":[{"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/pressbooks\/v2\/chapters\/197\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/wp\/v2\/media?parent=197"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/pressbooks\/v2\/chapter-type?post=197"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/wp\/v2\/contributor?post=197"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/wp\/v2\/license?post=197"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}