The Bewildered Brain: Asymmetric Brain Activity as a Source of Cognitive Impairment in Depression

Abstract

Individuals with depression commonly complain about cognitive deficits such as memory loss and poor decision making ability (Lahr, Beblo, & Hartje, 2007). However, despite considerable research, no single profile of cognitive deficits in depression has emerged (Ravnkilde et al., 2002). This may be a result of heterogeneity within the diagnostic category of depression. While typically diagnosed as a single disorder, the symptoms of depression may stem from different neurobiological causes leading to different profiles of cognitive deficits. Shenal, Harrison, and Demaree (2003) theorised that subtypes of depression could arise from dysfunctional brain activity in each of the quadrants of the brain (right frontal, left frontal, right posterior, and left posterior). For example, reduced left frontal activity in depression may be associated with impairments in tasks reliant on left frontal regions. Little research has directly investigated the possible link between variability in cognitive deficits and different patterns of dysfunctional brain activity in depression. The current paper reviews evidence for this link by describing depressed individuals’ performance on lateralised cognitive tasks, and discusses possibilities for future research.