Uploaded August 2026 | Updated September 2026, 1 week ago
Clinical depression is a disorder that affects mood, thinking, and behavior. In this video, I discuss several hypotheses regarding the neurobiological mechanisms that may contribute to depression.
🧠Take your learning further with my free, self-paced Introduction to Neuroscience course featuring my videos, articles, and hundreds of quiz questions: neuroscientificallychallenged.com/course
If you're looking for accessible and entertaining ways to learn more about the brain, check out my books:
đź“šYour Brain, Explained: What Neuroscience Reveals About Your Brain and its Quirks: amazon.com/dp/1473696569
đź“šBizarre: The Most Peculiar Cases of Human Behavior and What They Tell Us About How the Brain Works: amazon.com/dp/139980121X
TRANSCRIPT
Clinical depression is a disorder that affects mood, thinking, and behavior. Scientists do not yet fully understand the brain mechanisms underlying depression, in part because the disorder arises from a complex interplay of biological and environmental influences.
One of the best-known ideas about the biology of depression is the serotonin hypothesis, which proposed that depression is linked to reduced serotonin signaling. Although serotonin appears to play a role in depression in some individuals, researchers now recognize that the disorder cannot be explained by a simple serotonin deficiency. Instead, it seems to involve broader changes in brain function, such as alterations in other neurotransmitter systems and differences in the activity of brain networks involved in emotion, reward, and cognitive control.
Research has also implicated other biological systems in depression. One of these is the HPA axis, a major stress response system. In some people with depression, this system appears to be overactive, leading to elevated levels of the stress hormone cortisol. Over time, high cortisol levels may negatively affect brain regions involved in emotion, memory, and decision-making.
The immune system may be implicated in some cases of depression as well. Inflammatory molecules released by the immune system can influence neural activity, and chronic inflammation has been linked to changes in brain function and behavior that may contribute to depressive symptoms.
Some evidence also suggests that depression involves disruptions in neuroplasticity, the brain's ability to change and adapt throughout life. These disruptions may be related to reduced levels of BDNF, a protein that supports neuron growth and survival. Altered BDNF signaling could be linked to a decreased ability of the brain to adapt to experiences and stress in ways that promote psychological well-being.
REFERENCES
Krishnan V, Nestler EJ. The molecular neurobiology of depression. Nature. 2008 Oct 16;455(7215):894-902. doi: 10.1038/nature07455. PMID: 18923511; PMCID: PMC2721780.
Moncrieff J, Cooper RE, Stockmann T, Amendola S, Hengartner MP, Horowitz MA. The serotonin theory of depression: a systematic umbrella review of the evidence. Mol Psychiatry. 2023 Aug;28(8):3243-3256. doi: 10.1038/s41380-022-01661-0. Epub 2022 Jul 20. PMID: 35854107; PMCID: PMC10618090.
Otte C, Gold SM, Penninx BW, Pariante CM, Etkin A, Fava M, Mohr DC, Schatzberg AF. Major depressive disorder. Nat Rev Dis Primers. 2016 Sep 15;2:16065. doi: 10.1038/nrdp.2016.65. PMID: 27629598.
đź“ť Pass your next test with my neuroscience videos!
I’m Marc, a university professor at Penn State, and I’m here to take you on a journey into the fascinating world of the brain. I created this channel to break down complex topics into easy-to-understand snippets—perfect for both students and curious minds alike. 📚
My goal is to make learning neuroscience fun and accessible. Whether you're a student looking to supplement your studies or simply eager to understand the basics of the brain, this channel is for you.
Hit subscribe and get to know your brain, one video at a time! đź§
Clinical depression is a disorder that affects mood, thinking, and behavior. In this video, I discuss several hypotheses regarding the neurobiological mechanisms that may contribute to depression.
🧠Take your learning further with my free, self-paced Introduction to Neuroscience course featuring my videos, articles, and hundreds of quiz questions: neuroscientificallychallenged.com/course
If you're looking for accessible and entertaining ways to learn more about the brain, check out my books:
đź“šYour Brain, Explained: What Neuroscience Reveals About Your Brain and its Quirks: amazon.com/dp/1473696569
đź“šBizarre: The Most Peculiar Cases of Human Behavior and What They Tell Us About How the Brain Works: amazon.com/dp/139980121X
TRANSCRIPT
Clinical depression is a disorder that affects mood, thinking, and behavior. Scientists do not yet fully understand the brain mechanisms underlying depression, in part because the disorder arises from a complex interplay of biological and environmental influences.
One of the best-known ideas about the biology of depression is the serotonin hypothesis, which proposed that depression is linked to reduced serotonin signaling. Although serotonin appears to play a role in depression in some individuals, researchers now recognize that the disorder cannot be explained by a simple serotonin deficiency. Instead, it seems to involve broader changes in brain function, such as alterations in other neurotransmitter systems and differences in the activity of brain networks involved in emotion, reward, and cognitive control.
Research has also implicated other biological systems in depression. One of these is the HPA axis, a major stress response system. In some people with depression, this system appears to be overactive, leading to elevated levels of the stress hormone cortisol. Over time, high cortisol levels may negatively affect brain regions involved in emotion, memory, and decision-making.
The immune system may be implicated in some cases of depression as well. Inflammatory molecules released by the immune system can influence neural activity, and chronic inflammation has been linked to changes in brain function and behavior that may contribute to depressive symptoms.
Some evidence also suggests that depression involves disruptions in neuroplasticity, the brain's ability to change and adapt throughout life. These disruptions may be related to reduced levels of BDNF, a protein that supports neuron growth and survival. Altered BDNF signaling could be linked to a decreased ability of the brain to adapt to experiences and stress in ways that promote psychological well-being.
REFERENCES
Krishnan V, Nestler EJ. The molecular neurobiology of depression. Nature. 2008 Oct 16;455(7215):894-902. doi: 10.1038/nature07455. PMID: 18923511; PMCID: PMC2721780.
Moncrieff J, Cooper RE, Stockmann T, Amendola S, Hengartner MP, Horowitz MA. The serotonin theory of depression: a systematic umbrella review of the evidence. Mol Psychiatry. 2023 Aug;28(8):3243-3256. doi: 10.1038/s41380-022-01661-0. Epub 2022 Jul 20. PMID: 35854107; PMCID: PMC10618090.
Otte C, Gold SM, Penninx BW, Pariante CM, Etkin A, Fava M, Mohr DC, Schatzberg AF. Major depressive disorder. Nat Rev Dis Primers. 2016 Sep 15;2:16065. doi: 10.1038/nrdp.2016.65. PMID: 27629598.
đź“ť Pass your next test with my neuroscience videos!
I’m Marc, a university professor at Penn State, and I’m here to take you on a journey into the fascinating world of the brain. I created this channel to break down complex topics into easy-to-understand snippets—perfect for both students and curious minds alike. 📚
My goal is to make learning neuroscience fun and accessible. Whether you're a student looking to supplement your studies or simply eager to understand the basics of the brain, this channel is for you.
Hit subscribe and get to know your brain, one video at a time! đź§
