Experimental evidence for a motivational origin of cognitive impairment in major depression

Background. Diagnostic criteria and empirical evidence support the existence of cognitive deficits in depression. However, depressed mood, loss of interest and low self-efficacy might influence cognitive performance. Method. Goal-setting instructions were used to promote motivation in depressed patients and control subjects during neuropsychological assessment. The resulting performance was compared with performance using standard instructions. Sixty in-patients with non-psychotic unipolar depression and 60 age- and education-matched healthy control subjects were assessed with standard neuropsychological tests [the Auditory Verbal Learning Test (AVLT), the Digit Symbol Test (DST), the Regensburg Word Fluency Test (RWT), and the Number Combination Test (Zahlen-Verbindungs-Test, ZVT)] using either goal-setting or standard test instructions. Results. Depressed patients showed lower baseline performance and lower generalized self-efficacy (p < 0.0005) than controls. However, goal-setting instructions significantly improved patients' memory performance by 10% [AVLT: F(5,54)=3.611, p=0.007] and psychomotor performance by 13% [ZVT: F(3,56)=3.667, p=0.017]. Consequently, patients and control subjects demonstrated similar results when goal-setting instructions were applied. Goal-setting instructions showed a statistical trend, increasing patients' performance in the DST by 12 % [F(1, 58) = 2.990, p = 0.089], although their verbal fluency measured by the RWT did not increase. No significant correlations of increased performance with generalized self-efficacy were found. Conclusions. Cognitive deficits in depressed patients are influenced by motivational shortcomings. Because generalized self-efficacy failed to correlate to increased test performance, future research needs to disentangle the effective components of goal-setting instructions. Task-specific self-efficacy as well as enhancement of task-focused attention might underlie the significant goal-setting effect in depressed patients.