Depressed people are notorious for dwelling on the negative. A lot of people often think that it is something they can snap out of if they try hard enough, despite ample information on the Internet and other resources informing people that depressed individuals can’t simply change their attitude. There is a neurological reason for this.
It is observed that people with depression lack cognitive control. Cognitive Control is described on the Carter lab, University of California’s Translational Cognitive and Affective Neuroscience website as “processes that allow information processing and behavior to vary adaptively from moment to moment depending on current goals, rather than remaining rigid and inflexible”. It is this ability to adapt and be flexible in the brains of depressed people that is lacking, a part of this is selective attention.
It has been established, as cited in the by researchers in paper Emotional Dysfunction in Psychopathology and Neuropathology, that the dorsolateral prefrontal cortex is an area in the brain associated with executive functions including working memory and selective attention. It is precisely this area of the brain, on the left, that has been reported by a handful of studies, cited in the paper Improved Frustration Tolerance and Processing Speed by tDCS, to have relatively low activity levels in people with depression. This literally means that because of decreased activity in this area of the brain, which is responsible for our ability to control what we pay attention to, depressed individuals can’t control their negativity. This means depressed individuals can’t just stop themselves from thinking of negative things or being preoccupied with certain things because they have lost control of what they can focus on.