Biology of depression
Scientific studies have found that numerous brain areas show altered activity in patients suffering from depression, and this has encouraged advocates of various theories that seek to identify a biochemical origin of the disease, as opposed to theories that emphasize psychological or situational causes. Several theories concerning the biologically based cause of depression have been suggested over the years, of which the most prominent and widely researched is the monoamine hypothesis.
- 1 Genetic factors
- 2 Circadian rhythm
- 3 Monoamines
- 4 Abnormalities by brain region
- 5 Altered neuroplasticity
- 6 Large-scale brain network theory
- 7 References
- 8 Further reading
In contrast to other psychiatric disorders such as autism and schizophrenia, genetic factors involved in depression have been more difficult to identify. In 2003 Science published an influential study of Avshalom Caspi et al. who found that a gene-environment interaction (GxE) may explain why life stress is a predictor for depressive episodes in some individuals, but not in others, depending on an allelic variation of the serotonin-transporter-linked promoter region (5-HTTLPR). Soon after, the results were replicated by Kenneth Kendler's group, raising hopes in the psychiatric genetics community. By 2007 there were 11 replications, 3 partial replication and 3 non-replications of this proposed GxE. However, two of the largest studies were negative. Two 2009 meta-analyses were also negative; one included 14 studies, the other just five, owing to different study selection criteria. A 2010 review of studies in this area found 17 replications, 8 partial replications (interaction only in females or only with one of several types of adversity), and 9 non-replications (no interaction or an interaction in the opposite direction). It also found a systematic relationship between the method used to assess environmental adversity and the results of the studies; all studies using objective indicators or structured interviews to assess stress replicated the gene–environment interaction fully or partially, whereas all non-replications relied on brief self-report measures of adversity. This review also found that both 2009 meta-analyses were significantly biased toward negative studies.
Other hypothesized genomic influences are BDNF polymorphisms, but the replications studies have been mixed and insufficient as of 2005 for a meta-analysis. Studies also indicate an association of BDNF to suicidal behavior. However, findings from the gene-environment interactions studies suggest that the current BDNF models of depression are too simplistic. A 2008 study found interactions (biological epistasis) in the signaling pathways of the BDNF and the serotonin transporter; the BDNF Val66Met allele, which was predicted to have reduced responsitivity to serotonin, was found to exercise protective effects in individuals with the short 5-HTTLPR allele that is otherwise believed to predispose individuals to depressive episodes after stressful events. Thus, the BDNF-mediated signalling involved in neuroplastic responses to stress and antidepressants is influenced by other genetic and environmental modifiers.
The largest genome-wide study to date failed to identify variants with genome-wide significance in over 9000 cases.
Recently, the first genetics study has been published with positively identified two variants with genome-wide association with major depressive disorder. This study, conducted in Chinese Han woman, identified two variants in intronic regions near SIRT1 and LHPP.
Depression may be related to abnormalities in the circadian rhythm, or biological clock. For example, rapid eye movement (REM) sleep—the stage in which dreaming occurs—may be quick to arrive and intense in depressed people. REM sleep depends on decreased serotonin levels in the brain stem, and is impaired by compounds, such as antidepressants, that increase serotonergic tone in brain stem structures. Overall, the serotonergic system is least active during sleep and most active during wakefulness. Prolonged wakefulness due to sleep deprivation activates serotonergic neurons, leading to processes similar to the therapeutic effect of antidepressants, such as the selective serotonin reuptake inhibitors (SSRIs). Depressed individuals can exhibit a significant lift in mood after a night of sleep deprivation. SSRIs may directly depend on the increase of central serotonergic neurotransmission for their therapeutic effect, the same system that impacts cycles of sleep and wakefulness.
Research on the effects of light therapy on seasonal affective disorder suggests that light deprivation is related to decreased activity in the serotonergic system and to abnormalities in the sleep cycle, particularly insomnia. Exposure to light also targets the serotonergic system, providing more support for the important role this system may play in depression. Sleep deprivation and light therapy both target the same brain neurotransmitter system and brain areas as antidepressant drugs, and are now used clinically to treat depression. Light therapy, sleep deprivation and sleep time displacement (sleep phase advance therapy) are being used in combination quickly to interrupt a deep depression in hospitalized patients.
Monoamines are neurotransmitters and neuromodulators that include serotonin, dopamine, norepinephrine, and epinephrine. Many antidepressant drugs increase synaptic levels of the monoamine neurotransmitter, serotonin, but they may also enhance the levels of two other neurotransmitters, norepinephrine and dopamine. The observation of this efficacy led to the monoamine hypothesis of depression, which postulates that the deficit of certain neurotransmitters is responsible for the corresponding features of depression: "Norepinephrine may be related to alertness and energy as well as anxiety, attention, and interest in life; [lack of] serotonin to anxiety, obsessions, and compulsions; and dopamine to attention, motivation, pleasure, and reward, as well as interest in life." The proponents of this hypothesis recommend choosing the antidepressant with the mechanism of action impacting the most prominent symptoms. Anxious or irritable patients should be treated with SSRIs or norepinephrine reuptake inhibitors, and the ones with the loss of energy and enjoyment of life—with norepinephrine and dopamine enhancing drugs.
Consistent with the monoamine hypothesis, a longitudinal study uncovered a moderating effect of the serotonin transporter (5-HTT) gene on stressful life events in predicting depression. Specifically, depression seems especially likely to follow stressful life events, but even more so for people with one or two short alleles of the 5-HTT gene. Serotonin may help to regulate other neurotransmitter systems, and decreased serotonin activity may "permit" these systems to act in unusual and erratic ways. Facets of depression may be emergent properties of this dysregulation.
An offshoot of the monoamine hypothesis suggests that monoamine oxidase A (MAO-A), an enzyme which metabolizes monoamines, may be overly active in depressed people. This would, in turn, cause the lowered levels of monoamines. This hypothesis received support from a PET study, which found significantly elevated activity of MAO-A in the brain of some depressed people. In genetic studies, the alterations of MAO-A-related genes have not been consistently associated with depression. Contrary to the assumptions of the monoamine hypothesis, lowered but not heightened activity of MAO-A was associated with the depressive symptoms in youth. This association was observed only in maltreated youth, indicating that both biological (MAO genes) and psychological (maltreatment) factors are important in the development of depressive disorders. In addition, some evidence indicates that problems in information processing within neural networks, rather than changes in chemical balance, might underlie depression.
Since the 1990s, research has uncovered multiple limitations of the monoamine hypothesis, and its inadequacy has been criticized within the psychiatric community. For one thing, serotonin system dysfunction cannot be the sole cause of depression; antidepressants usually bring serotonin levels up to normal very quickly, but it often takes at least two to four weeks before mood improves significantly. Intensive investigation has failed to find convincing evidence of a primary dysfunction of a specific monoamine system in patients with major depressive disorders. The antidepressants that do not act through the monoamine system, such as tianeptine and opipramol, have been known for a long time. Experiments with pharmacological agents that cause depletion of monoamines have shown that this depletion does not cause depression in healthy people nor does it worsen the symptoms in depressed patients. Already limited, the monoamine hypothesis has been further oversimplified when presented to the general public.
Abnormalities by brain region
Research on the brains of depressed patients usually shows disturbed patterns of interaction between multiple parts of the brain. Several areas of the brain are implicated in studies seeking to more fully understand the biology of depression:
The sole source of serotonin in the brain is the raphe nuclei, a group of small nerve cell nuclei in the upper brain stem, located directly at the mid-line of the brain. There is some evidence for neuropathological abnormalities in the rostral raphe nuclei in depression. Despite their small size, they reach very widely through their projections, and are involved in a very diverse set of functions. Most antidepressants are serotonergic.
Suprachiasmatic nucleus (SCN)
The suprachiasmatic nucleus (SCN) is the control center for the body's "biological clock." It contains neurons whose activity waxes and wanes throughout the day. The output from the SCN controls the sleep/wake cycle as well as a number of other biological rhythms, such as fluctuations in body temperature. Disturbances of these cycles are a consistent symptom of depression, especially of the melancholic type. The "classic" pattern is for depressed people to have great difficulty falling asleep at night, and then to wake bolt upright at around 3 AM. The waking is usually preceded by a rise in body temperature, which in non-depressed people does not usually occur until several hours later. It is a common observation that antidepressants produce a return to normal sleep patterns before they produce an improvement in mood: if good sleep does not return, it is a strong sign that the treatment is not going to be effective. Conversely, disruptions to sleep are often the first indication of impending relapse.
There is a powerful interaction between the Raphe nuclei and the SCN. On one hand, the Raphe nuclei send a strong serotonergic projection to the SCN. In animal studies, this input has been shown to modulate the ability of light to reset the timing of the biological clock: the more serotonin, the stronger the effects of light. On the other hand, the biological clock exerts a strong influence on the Raphe nuclei: serotonin levels drop during sleep, and fall almost to nothing during REM (dreaming) sleep. It is worth noting that one of the characteristics of sleep in depressed people is that REM tends to appear very soon after sleep onset, whereas in non-depressed people it does not usually dominate sleep until the last hours, in the early morning. Antidepressants are powerful suppressors of REM.
Ventral tegmental area (VTA)
The ventral tegmentum (or ventral tegmental area) is a small area in the basal midbrain which is a critical part of the brain's reward system. It sends projections to the nucleus accumbens that use the neurotransmitter dopamine. Addictive drugs universally increase the effects of dopamine in this system, whereas drugs that oppose dopamine produce anhedonia of the sort seen in depressed people. Dopamine-enhancers such as cocaine often relieve the lack-of-pleasure in depression, but the effects only last as long as a drug is present in the body: that is, they temporarily alleviate one of the main symptoms, but do not help to cure the disease.
Nucleus accumbens (NAc)
Anterior cingulate cortex (ACC)
The anterior cingulate cortex is activated by negative experiences of many types, and consistently shows higher levels of activity in depressed people than in non-depressed people. The functions of the ACC are controversial, but one proposal is that it mediates the conscious experience of suffering. Several decades ago, trials were made of ablating parts of the ACC in an attempt to relieve intolerable pain in patients who were terminally ill. These patients reported that after the surgery, they could still perceive the physical sensations of pain, but they no longer found them distressing. (The effects of heroin and morphine are sometimes described in the same way.) Very recently, clinical experiments were made in using deep brain stimulation to temporarily inactivate the ACC in severely depressed patients. This was not effective in all cases, but in some patients very striking results were achieved, with a perceptible lifting of mood immediately apparent to the patient as soon as the stimulus was applied.
Recent studies have shown that Brodmann area 25, also known as Subgenual cingulate is metabolically overactive in treatment-resistant depression. This region is extremely rich in serotonin transporters and is considered as a governor for a vast network involving areas like hypothalamus and brain stem, which influences changes in appetite and sleep; the amygdala and insula, which affect the mood and anxiety; the hippocampus, which plays an important role in memory formation; and some parts of the frontal cortex responsible for self-esteem. Thus disturbances in this area or a smaller than normal size of this area contributes to depression. Deep Brain Stimulations of this area have been successful in reducing its elevated activity and thus curing depression in patients that could not be cured by anti-depressants.
Hypothalamic-pituitary-adrenal (HPA) axis
The hypothalamic-pituitary-adrenal axis is a chain of endocrine structures that are activated during the body's response to stressors of various sorts. It often shows increased activation in depressed people, but the mechanism behind this is not yet known.
Multiple studies have found evidence of ventricular enlargement in people who have depression, particularly enlargement of the third ventricle. These observations are interpreted as indicating loss of neural tissue in brain regions adjacent to the enlarged ventricle, leading to suggestions that cytokines and related mediators of neurodegeneration may play a role in giving rise to the disease.
Recent studies have called attention to the role of altered neuroplasticity in depression. A review found convergence of three phenomena:
- Chronic stress reduces synaptic and dendritic plasticity
- Depressed subjects show evidence of impaired neuroplasticity (e.g. shortening and reduced complexity of dendritic trees)
- Anti-depressant medications enhance neuroplasticity at both a molecular and dendritic level.
The conclusion is that disrupted neuroplasticity is an underlying feature of depression, and is reversed by antidepressants.
Large-scale brain network theory
Instead of studying one brain region, studying large scale brain networks is another approach to understanding psychiatric and neurological disorders, supported by recent research that has shown that multiple brain regions are involved in these disorders. Understanding the disruptions in these networks may provide important insights into interventions for treating these disorders. Recent work suggests that at least three large-scale brain networks are important in psychopathology:
Central executive network
The executive network is made up of fronto-parietal regions, including dorsolateral prefrontal cortex and lateral posterior parietal cortex. This network is crucially involved in high level cognitive functions such as maintaining and using information in working memory, problem solving, and decision making. Deficiencies in this network are common in most major psychiatric and neurological disorders, including depression. Because this network is crucial for everyday life activities, those who are depressed can show impairment in basic activities like test taking and being decisive.
Default mode network
The default mode network includes hubs in the prefrontal cortex and posterior cingulate, with other prominent regions of the network in the medial temporal lobe and angular gyrus. The default mode network is usually active during mind-wandering and thinking about social situations. In contrast, during specific tasks probed in cognitive science (for example, simple attention tasks), the default network is often deactivated. Research has shown that regions in the default mode network (including medial prefrontal cortex and posterior cingulate) show greater activity when depressed participants ruminate (that is, when they engage in repetitive self-focused thinking) than when typical, healthy participants ruminate. Individuals suffering from major depression also show increased connectivity between the default mode network and the subgenual cingulate and the adjoining ventromedial prefrontal cortex in comparison to healthy individuals, individuals with dementia or with autism. Numerous studies suggest that the subgenual cingulate plays an important role in the dysfunction that characterizes major depression. The increased activation in the default mode network during rumination and the atypical connectivity between core default mode regions and the subgenual cingulate may underlie the tendency for depressed individual to get “stuck” in the negative, self-focused thoughts that often characterize depression. However, further research is needed to gain a precise understanding of how these network interactions map to specific symptoms of depression.
The salience network is a cingulate-frontal operculum network that includes core nodes in the anterior cingulate and anterior insula. A salience network is a large-scale brain network involved in detecting and orienting the most pertinent of the external stimuli and internal events being presented. Individuals who have a tendency to experience negative emotional states (scoring high on measures of neuroticism) show an increase in the right anterior insula during decision-making, even if the decision has already been made. This atypically high activity in the right anterior insula is thought to contribute to the experience of negative and worrisome feelings. In major depressive disorder, anxiety is often a part of the emotional state that characterizes depression.
- Nierenberg, AA (2009). "The long tale of the short arm of the promoter region for the gene that encodes the serotonin uptake protein" (PDF). CNS spectrums 14 (9): 462–3. PMID 19890228.
- Caspi, A.; Sugden, K.; Moffitt, T. E.; Taylor, A.; Craig, I. W.; Harrington, H.; McClay, J.; Mill, J.; Martin, J.; Braithwaite, A.; Poulton, R. (2003). "Influence of Life Stress on Depression: Moderation by a Polymorphism in the 5-HTT Gene". Science 301 (5631): 386–389. Bibcode:2003Sci...301..386C. doi:10.1126/science.1083968. PMID 12869766.
- Kendler, K.; Kuhn, J.; Vittum, J.; Prescott, C.; Riley, B. (2005). "The interaction of stressful life events and a serotonin transporter polymorphism in the prediction of episodes of major depression: a replication". Archives of General Psychiatry 62 (5): 529–535. doi:10.1001/archpsyc.62.5.529. PMID 15867106.
- Gillespie, N. A.; Whitfield, J. B.; Williams, B.; Heath, A. C.; Martin, N. G. (2005). "The relationship between stressful life events, the serotonin transporter (5-HTTLPR) genotype and major depression". Psychological Medicine 35 (1): 101–111. doi:10.1017/S0033291704002727. PMID 15842033.
- Surtees, P.; Wainwright, N.; Willis-Owen, S.; Luben, R.; Day, N.; Flint, J. (2006). "Social adversity, the serotonin transporter (5-HTTLPR) polymorphism and major depressive disorder". Biological Psychiatry 59 (3): 224–229. doi:10.1016/j.biopsych.2005.07.014. PMID 16154545.
- Uher, R.; McGuffin, P. (2008). "The moderation by the serotonin transporter gene of environmental adversity in the aetiology of mental illness: review and methodological analysis". Molecular psychiatry 13 (2): 131–146. doi:10.1038/sj.mp.4002067. PMID 17700575.
- Risch, N.; Herrell, R.; Lehner, T.; Liang, K.; Eaves, L.; Hoh, J.; Griem, A.; Kovacs, M.; Ott, J.; Merikangas, K. R. (2009). "Interaction between the serotonin transporter gene (5-HTTLPR), stressful life events, and risk of depression: a meta-analysis". Journal of the American Medical Association 301 (23): 2462–2471. doi:10.1001/jama.2009.878. PMC 2938776. PMID 19531786.
- Munafo, M.; Durrant, C.; Lewis, G.; Flint, J. (2009). "Gene × Environment Interactions at the Serotonin Transporter Locus". Biological Psychiatry 65 (3): 211–219. doi:10.1016/j.biopsych.2008.06.009. PMID 18691701.
- Uher, R.; McGuffin, P. (2010). "The moderation by the serotonin transporter gene of environmental adversity in the etiology of depression: 2009 update". Molecular psychiatry 15 (1): 18–22. doi:10.1038/mp.2009.123. PMID 20029411.
- Levinson, D. (2006). "The genetics of depression: a review". Biological Psychiatry 60 (2): 84–92. doi:10.1016/j.biopsych.2005.08.024. PMID 16300747.
- Dwivedi Y (2009). "Brain-derived neurotrophic factor: role in depression and suicide". Neuropsychiatr Dis Treat 5: 433–49. doi:10.2147/NDT.S5700. PMC 2732010. PMID 19721723.
- Krishnan, V.; Nestler, E. (2008). "The molecular neurobiology of depression". Nature 455 (7215): 894–902. Bibcode:2008Natur.455..894K. doi:10.1038/nature07455. PMC 2721780. PMID 18923511.
- Pezawas, L.; Meyer-Lindenberg, A.; Goldman, A. L.; Verchinski, B. A.; Chen, G.; Kolachana, B. S.; Egan, M. F.; Mattay, V. S.; Hariri, A. R.; Weinberger, D. R. (2008). "Evidence of biologic epistasis between BDNF and SLC6A4 and implications for depression". Molecular Psychiatry 13 (7): 709–716. doi:10.1038/mp.2008.32. PMID 18347599.
- Major Depressive Disorder Working Group of the Psychiatric GWAS Consortium; Ripke, S; Wray, N. R.; Lewis, C. M.; Hamilton, S. P.; Weissman, M. M.; Breen, G; Byrne, E. M.; Blackwood, D. H.; Boomsma, D. I.; Cichon, S; Heath, A. C.; Holsboer, F; Lucae, S; Madden, P. A.; Martin, N. G.; McGuffin, P; Muglia, P; Noethen, M. M.; Penninx, B. P.; Pergadia, M. L.; Potash, J. B.; Rietschel, M; Lin, D; Müller-Myhsok, B; Shi, J; Steinberg, S; Grabe, H. J.; Lichtenstein, P; et al. (2013). "A mega-analysis of genome-wide association studies for major depressive disorder". Molecular Psychiatry 18 (4): 497–511. doi:10.1038/mp.2012.21. PMC 3837431. PMID 22472876.
- Converge, Consortium; Bigdeli, Tim B.; Kretzschmar, Warren; Li, Yihan; Liang, Jieqin; Song, Li; Hu, Jingchu; Li, Qibin; Jin, Wei; Hu, Zhenfei; Wang, Guangbiao; Wang, Linmao; Qian, Puyi; Liu, Yuan; Jiang, Tao; Lu, Yao; Zhang, Xiuqing; Yin, Ye; Li, Yingrui; Xu, Xun; Gao, Jingfang; Reimers, Mark; Webb, Todd; Riley, Brien; Bacanu, Silviu; Peterson, Roseann E.; Chen, Yiping; Zhong, Hui; Liu, Zhengrong; et al. (2015). "Sparse whole-genome sequencing identifies two loci for major depressive disorder". Nature 523 (7562): 588–91. doi:10.1038/nature14659. PMC 4522619. PMID 26176920.
- Carlson, N. (2013). Physiology of behavior. (11 ed., pp. 578-582). United States of America: Pearson.
- Adrien J.. Neurobiological bases for the relation between sleep and depression. Sleep Medicine Review. 2003;6(5):341–51. doi:10.1053/smrv.2001.0200. PMID 12531125.
- Carlson, N. (2013). Physiology of behavior. (11 ed., pp. 578-580). United States of America: Pearson.
- Terman M. Evolving applications of light therapy. Sleep Medicine Review. 2007;11(6):497–507. doi:10.1016/j.smrv.2007.06.003. PMID 17964200.
- Benedetti F, Barbini B, Colombo C, Smeraldi E. Chronotherapeutics in a psychiatric ward. Sleep Medicine Review. 2007;11(6):509–22. doi:10.1016/j.smrv.2007.06.004. PMID 17689120.
- Neil Carlson: Foundations of Physiological Psychology, 6th ed. 2005. ISBN 0-205-42723-5 Page: 108
- Nutt DJ (2008). "Relationship of neurotransmitters to the symptoms of major depressive disorder". Journal of Clinical Psychiatry. 69 Suppl E1: 4–7. PMID 18494537.
- Carlson, N. (2013). Physiology of behavior. (11 ed., pp. 575-576). United States of America: Pearson.
- Avshalom Caspi, Karen Sugden, Terrie E. Moffitt, Alan Taylor, Ian W. Craig, HonaLee Harrington, Joseph McClay, Jonathan Mill, Judy Martin, Antony Braithwaite, and Richie Poulton (July 2003). "Influence of Life Stress on Depression: Moderation by a Polymorphism in the 5-HTT Gene". Science 301 (5631): 386–389. doi:10.1126/science.1083968. PMID 12869766.
- Caspi A; et al. (2003). "Influence of life stress on depression: Moderation by a polymorphism in the 5-HTT gene". Science 301 (5631): 386–89. Bibcode:2003Sci...301..386C. doi:10.1126/science.1083968. PMID 12869766.
- Mandell AJ, Knapp S (1979). "Asymmetry and mood, emergent properties of serotonin regulation: A proposed mechanism of action of lithium". Archives of General Psychiatry 36 (8): 909–16. doi:10.1001/archpsyc.1979.01780080083019. PMID 454111.
- Meyer JH, Ginovart N, Boovariwala A; et al. (November 2006). "Elevated monoamine oxidase a levels in the brain: An explanation for the monoamine imbalance of major depression". Archives of General Psychiatry 63 (11): 1209–16. doi:10.1001/archpsyc.63.11.1209. PMID 17088501.
- Huang SY, Lin MT, Lin WW; Huang CC; Shy MJ; Lu RB (2007-12-19). "Association of monoamine oxidase A (MAOA) polymorphisms and clinical subgroups of major depressive disorders in the Han Chinese population". World Journal of Biological Psychiatry (Informa Healthcare) 10 (4 Pt 2): 544–51. doi:10.1080/15622970701816506. PMID 19224413. Retrieved 2008-09-20.
- Yu YW, Tsai SJ, Hong CJ, Chen TJ, Chen MC, Yang CW (September 2005). "Association study of a monoamine oxidase a gene promoter polymorphism with major depressive disorder and antidepressant response". Neuropsychopharmacology 30 (9): 1719–23. doi:10.1038/sj.npp.1300785. PMID 15956990.
- Cicchetti D, Rogosch FA, Sturge-Apple ML (2007). "Interactions of child maltreatment and serotonin transporter and monoamine oxidase A polymorphisms: depressive symptomatology among adolescents from low socioeconomic status backgrounds". Dev. Psychopathol. 19 (4): 1161–80. doi:10.1017/S0954579407000600. PMID 17931441.
- Castrén, E (2005). "Is mood chemistry?". Nature Reviews Neuroscience 6 (3): 241–46. doi:10.1038/nrn1629. PMID 15738959.
- Hirschfeld RM (2000). "History and evolution of the monoamine hypothesis of depression". Journal of Clinical Psychiatry. 61 Suppl 6: 4–6. PMID 10775017.
- Delgado PL, Moreno FA (2000). "Role of norepinephrine in depression". J Clin Psychiatry. 61 Suppl 1: 5–12. PMID 10703757.
- Delgado PL (2000). "Depression: the case for a monoamine deficiency". Journal of Clinical Psychiatry. 61 Suppl 6: 7–11. PMID 10775018.
- Lacasse J, Leo J (2005). "Serotonin and Depression: A Disconnect between the Advertisements and the Scientific Literature". PLoS Med 2 (12): e392. doi:10.1371/journal.pmed.0020392. PMC 1277931. PMID 16268734. Free full text, open-access source
- Underwood MD, Khaibulina AA, Ellis SP, Moran A, Rice PM, Mann JJ, Arango V (August 1999). "Morphometry of the dorsal raphe nucleus serotonergic neurons in suicide victims". Biol Psychiatry 46 (4): 473–83. doi:10.1016/S0006-3223(99)00043-8. PMID 10459396.
- Arango V, Underwood MD, Boldrini M, Tamir H, Kassir SA, Hsiung S, Chen JJ, Mann JJ (December 2001). "Serotonin 1A receptors, serotonin transporter binding and serotonin transporter mRNA expression in the brainstem of depressed suicide victims". Neuropsychopharmacology 25 (6): 892–903. doi:10.1016/S0893-133X(01)00310-4. PMID 11750182.
- Matthews PR, Harrison PJ (March 2012). "A morphometric, immunohistochemical, and in situ hybridization study of the dorsal raphe nucleus in major depression, bipolar disorder, schizophrenia, and suicide". J Affect Disord 137 (1–3): 125–134. doi:10.1016/j.jad.2011.10.043. PMC 3314923. PMID 22129767.
- Di Chiara G, Loddo P, Tanda G (1999). "Reciprocal changes in prefrontal and limbic dopamine responsiveness to aversive and rewarding stimuli after chronic mild stress: implications for the psychobiology of depression". Biol. Psychiatry 46 (12): 1624–33. doi:10.1016/S0006-3223(99)00236-X. PMID 10624543.
- Scheggi S, Leggio B, Masi F; et al. (2002). "Selective modifications in the nucleus accumbens of dopamine synaptic transmission in rats exposed to chronic stress". J. Neurochem. 83 (4): 895–903. doi:10.1046/j.1471-4159.2002.01193.x. PMID 12421362.
- Rossetti ZL, Lai M, Hmaidan Y, Gessa GL (1993). "Depletion of mesolimbic dopamine during behavioral despair: partial reversal by chronic imipramine". Eur. J. Pharmacol. 242 (3): 313–5. doi:10.1016/0014-2999(93)90257-I. PMID 8281997.
- Mayberg HS, Brannan SK, Tekell JL, Silva JA, Mahurin RK, McGinnis S, Jerabek PA (Oct 2000). "Regional metabolic effects of fluoxetine in major depression: serial changes and relationship to clinical response". Biol Psychiatry 48 (8): 830–43. doi:10.1016/s0006-3223(00)01036-2. PMID 11063978.
- Carlson, N. (2013). Physiology of behavior. (11 ed., pp. 576-578). United States of America: Pearson.
- "Faulty Circuits", Scientific American, April 2010
- Mayberg Helen S., Lozano Andres M., Voon Valerie, McNeely Heather E., Seminowicz David, Hamani Clement, Schwalb Jason M., Kennedy Sidney H. (2005). "Deep Brain Stimulation for Treatment-Resistant Depression .". Neuron 45 (5): 651–660. doi:10.1016/j.neuron.2005.02.014. PMID 15748841.
- Pariante CM, Lightman SL. (September 2008). "The HPA axis in major depression: classical theories and new developments.". Trends Neurosci. 31 (9): :464–468. doi:10.1016/j.tins.2008.06.006. PMID 18675469.
- Hendrie, C.A.; Pickles, A.R. (2009). "Depression as an evolutionary adaptation: Implications for the development of preclinical models". Medical Hypotheses 72 (3): 342–347. doi:10.1016/j.mehy.2008.09.053. PMID 19153014. Retrieved September 25, 2013.
- Hendrie, C.A.; Pickles, A.R. (2010). "Depression as an evolutionary adaptation: Anatomical organisation around the third ventricle". Medical Hypotheses 74 (4): 735–740. doi:10.1016/j.mehy.2009.10.026. PMID 19931308. Retrieved September 25, 2013.
- Sheline, Yvette (August 2003). "Neuroimaging studies of mood disorder effects on the brain". Biological Psychiatry 54 (3): 338–352. doi:10.1016/s0006-3223(03)00347-0. PMID 12893109. Retrieved September 25, 2013.
- Manji, Husseini K.; Quiroz, Jorge A.; Sporn, Jonathan; Payne, Jennifer L.; Denicoff, Kirk; Gray, Neil A.; Zarate Jr., Carlos A.; Charney, Dennis S. (April 2003). "Enhancing neuronal plasticity and cellular resilience to develop novel, improved therapeutics for difficult-to-treat depression". Biological Psychiatry 53: 707–742. doi:10.1016/s0006-3223(03)00117-3. Retrieved September 25, 2013.
- Miller, A. H.; Maletic, V.; Raison, C. L. (2009). "Inflammation and its discontents: the role of cytokines in the pathophysiology of major depression". Biological Psychiatry 65 (9): 732–741. doi:10.1016/j.biopsych.2008.11.029. PMID 19150053.
- Raison, C. L.; Capuron, L.; Miller, A. H. (2006). "Cytokines sing the blues: inflammation and the pathogenesis of depression". Trends in Immunology 27 (1): 24–31. doi:10.1016/j.it.2005.11.006. PMC 3392963. PMID 16316783.
- Christopher Pittenger and Ronald S Duman (2008). "Stress, Depression, and Neuroplasticity: A Convergence of Mechanisms". Neuropsychopharmacology 33 (1): 88–109. doi:10.1038/sj.npp.1301574. PMID 17851537
- Menon, Vinod (October 2011). "Large-scale brain networks and psychopathology: a unifying triple network model". Trends in Cognitive Sciences 15 (10): 483–506. doi:10.1016/j.tics.2011.08.003. PMID 21908230.
- Seeley, W.W; et al. (February 2007). "Dissociable intrinsic connectivity networks for salience processing and executive control". The Journal of Neuroscience 27.
- Habas, C; et al. (1 July 2009). "Distinct cerebellar contributions to intrinsic connectivity networks". The Journal of Neuroscience 29.
- Petrides, M (2005). "Lateral prefrontal cortex: architecture and functional organization". Philosophical Transactions of the Royal Society B 360 (1456): 781–795. doi:10.1098/rstb.2005.1631.
- Koechlin, E; Summerfield, C (2007). "An information theoretical approach to prefrontal executive function". Trends in Cognitive Sciences 11 (6): 229–235. doi:10.1016/j.tics.2007.04.005. PMID 17475536.
- Miller, E.K.; Cohen, J.D. (2001). "An integrative theory of prefrontal cortex function". Annual Review of Neuroscience 24: 167–202. doi:10.1146/annurev.neuro.24.1.167. PMID 11283309.
- Muller, N.G.; Knight, R.T. (2006). "The functional neuroanatomy of working memory: contributions of human brain lesion studies". Neuroscience 139 (1): 51–58. doi:10.1016/j.neuroscience.2005.09.018. PMID 16352402.
- Woodward, N.D.; et al. (2011). "Functional resting-state networks are differentially affected in schizophrenia". Schizophrenia Research 130 (1–3): 86–93. doi:10.1016/j.schres.2011.03.010. PMC 3139756. PMID 21458238.
- Menon, Vinod; et al. (2001). "Functional neuroanatomy of auditory working memory in schizophrenia: relation to positive and negative symptoms". Neuroimage 13 (3): 433–446. doi:10.1006/nimg.2000.0699. PMID 11170809.
- Levin, R.L.; et al. (2007). "Cognitive deficits in depression and functional specificity of regional brain activity". Cognitive Therapy and Research 31 (2): 211–233. doi:10.1007/s10608-007-9128-z.
- Qin, P; Northoff, G (2011). "How is our self related to midline regions and the default mode network?". Neuroimage 57 (3): 1221–1233. doi:10.1016/j.neuroimage.2011.05.028. PMID 21609772.
- Raichle, M.E.; et al. (2001). "A default mode of brain function". Proceedings of the National Academy of Sciences of the United States of America 98 (2): 676–682. doi:10.1073/pnas.98.2.676. PMC 14647. PMID 11209064.
- Cooney, R.E.; et al. (2010). "Neural correlates of rumination in depression". Cognitive Affective and Behavioral Neuroscience 10 (4): 470–478. doi:10.3758/cabn.10.4.470.
- Broyd, S.J.; et al. (2009). "Default mode brain dysfunction in mental disorders: a systematic review". Neuroscience & Biobehavioral Reviews 33 (3): 279–296. doi:10.1016/j.neubiorev.2008.09.002. PMID 18824195.
- Hamani, C; et al. (15 February 2011). "The subcallosal cingulate gyrus in the context of major depression". Biological Psychiatry 69 (4): 301–8. doi:10.1016/j.biopsych.2010.09.034. PMID 21145043.
- Feinstein, J.S.; et al. (September 2006). "Anterior insula reactivity during certain decisions is associated with neuroticism". Social Cognition and Affective Neuroscience 1 (2): 136–142. doi:10.1093/scan/nsl016.
- Paulus, M.P; Stein, M.B. (2006). "An insular view of anxiety". Biological Psychiatry 60 (4): 383–387. doi:10.1016/j.biopsych.2006.03.042. PMID 16780813.
- Antony, M.M. (2009). Oxford Handbook of Anxiety and Related Disorders. Oxford University Press.
- Szafran K, Faron-Górecka A, Kolasa M; et al. (2013). "Potential role of G protein-coupled receptor (GPCR) heterodimerization in neuropsychiatric disorders: a focus on depression". Pharmacol Rep 65 (6): 1498–505. doi:10.1016/s1734-1140(13)71510-x. PMID 24552997.
- Naumenko VS, Popova NK, Lacivita E, Leopoldo M, Ponimaskin EG (2014). "Interplay between serotonin 5-HT1A and 5-HT7 receptors in depressive disorders". CNS Neurosci Ther 20 (7): 582–90. doi:10.1111/cns.12247. PMID 24935787.