The Biological Basis of Depression (Major Depressive Disorder)

The Biological Basis of Depression (Major Depressive Disorder)

– refers to distress or disability arising from abnormally negative mood
– common symptoms: feelings of hopelessness; loss of enjoyment in activities
– our understanding of the cause is still very limited
– fMRI studies show no consistent brain explanations or abnormalities
– however, some abnormal activity has been found within the frontal lobes (showing less activity)
– limbic structures (also show increased activity)
[note: how these areas of the brain are involved in emotion regulation]
– in regards to stress, it has also been found that there are abnormal blood concentrations of certain hormones associated with stress (such as cortisol, a major stress hormone)
– the part of the brain that controls stress hormones is called the hypothalamus
– the hypothalamus communicates back & forth with the frontal lobes & the limbic system structures of the brain
– the stress hormones affect all tissues in the body & the structures above in the brain
– note: still to be understood is whether the stress hormones are the cause or the effect of depression
– there also appears to be differences/abnormalities in neuronal pathways & the use of neurotransmitters (which communicate), resulting in increased or decreased activity in the frontal lobes & the limbic structures
– one of these pathways start in what is called the raphe nuclei of the brain stem (located in several areas along the brain stem)
– they send projections up to many areas of the cerebrum, including the frontal lobes & the limbic structures
– they are responsible for much of the serotonin that is produced by the brain
– another pathway is located in the locus coeruleus (also in the brain stem)
– it transmits the neurotransmitter norepinephrine
– another pathway called the VTA (ventral tegmental area) & also in the brainstorm
– it transmits dopamine to the brain
[note: there are serotonin, norepinephrine & dopamine abnormalities often associated with major depression]
– a newer theory is that depression may in fact be linked to abnormalities in neuroplasticity (in particular how the brain changes as a result of experience) – animal studies seem to suggest this; however, again it is not certain whether neuroplasticity is the cause or the effect of depression
– genetic studies point to a genetic predisposition towards depression which may run in families & which increases the risk of the brain developing abnormal responses to negative or stressful events [biological explanation]
– psychosocial explanations for depression [childhood abuse; stressful events; limited social support during adverse childhood experiences]
[also known as biopsychosocial explanation informing a biopsychosocial approach to treatment]

Source: The Khan Academy @


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