Background: Most of the available evidence on the effects of depression is based on in- and out-patient samples focusing on individuals suffering from major depression. The aims of this study were to examine cognitive functioning in population-based samples and to determine whether cognitive performance varies as a function of depression subgroup.
Method: Population-based samples (aged 20-64 years) with major depression (N = 68), dysthymia (N = 28), mixed anxiety-depressive disorder (N = 25) and minor depression (N = 66) were examined on a variety of cognitive tasks (i.e. episodic memory, verbal fluency, perceptual-motor speed and mental flexibility). One hundred and seventy-five non-depressed individuals served as controls.
Results: The total group of depressed individuals showed impairments in tasks tapping episodic memory and mental flexibility. Of more interest, however, was the observation that the pattern of impairments varied as a function of depression subgroup: the major depression and mixed anxiety-depressive disorder groups exhibited significant memory dysfunction, whereas individuals with dysthymia showed pronounced difficulties in mental flexibility. Minor depression did not affect cognitive performance. Verbal fluency and perceptual-motor speed were not affected by depression.
Conclusions: These results indicate that persons with depressive disorders in the population exhibit cognitive impairments in tasks tapping episodic memory and mental flexibility and that cognitive impairment varies as a function of depressive disorder.