The impact of clinical depression on working memory

Introduction. Both Channon, Baker, and Robertson (1993) and Hartlage, Alloy, Vazquez, and Dykman (1993) claim that working memory impairment in depressed patients is limited to Baddeley's (1996) central executive and does not affect either the phonological loop or the visuospatial scratchpad. Our key questions were: (1) is there an impairment of working memory in depression and which elements does it effect; (2) is another major clinical group also affected and in what ways, and finally, (3) how do these groups vary when compared with each other and with normals? Thus we sought to locate a depression-specific effect and define its extent. Methods. We tested 35 depressed patients, using both 24 anxiety patients and 29 normal controls as comparisons. Several tasks were used so that we could differentiate between the three key aspects of working memory. Results. Contrary to Channon et al., we found that depression affects the allocation of attention and all elements of working memory. The depression group showed a distinct performance profile, with impairments occurring on measures of both the phonological loop and visuospatial sketch pad. On measures of central executive functioning, both depression and anxiety groups showed comparable levels of impairment when compared with the control group. Conclusions. We propose that the source of general disruption in both depressed and anxious patients may be a competition between attempts to direct attentional resources to the task in hand and away from the distractive and intrusive effects of automatic negative thoughts.