New cases of depression are common after traumatic brain injury. But it is not fully understood whether the depression is directly related to a brain injury, or if it is an indirect result of negative lifestyle changes after a brain injury.
Emotional symptoms of depression such as sadness, lack of motivation, or feelings of worthlessness have been linked to the right hemisphere of the brain. Therefore, if depression were directly related to a brain injury, lesions would occur more often in the right hemisphere.
In a study that compared MRI scans of brain-injured patients with depression to MRI scans of brain-injured patients without depression, the right hemisphere was confirmed to be related to new cases of depression-but, not in terms of lesions. Instead, newly depressed brain injury patients had a relatively larger right frontal lobe and relatively smaller parietal lobe than patients without depression.
This kind of imbalance can create a negative valence of emotions and lowered levels of arousal. The enlargement of one brain area and the atrophy of another are most likely to be the result of brain changes over time. This current study suggests that, over time, negative aspects of lifestyle after a brain injury are more likely to be responsible for depression than direct injury to the brain.
Schonberger M, Ponsford J, Reutens D, et al. The relationship between mood disorders and MRI findings following traumatic brain injury. Brain Injury. (June 2011).