Cognitive impairment in depression: a systematic review and meta-analysis

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Abstract

Background

This review aimed to address the question of whether cognitive impairment should be considered a core feature of depression that may be a valuable target for treatment.

Method

We conducted a systematic review and meta-analysis of cognitive function, assessed with a single neuropsychological test battery, the Cambridge Neuropsychological Test Automated Battery (CANTAB), in patients with depression during symptomatic and remitted states. Inclusion of studies comparing patients remitted from depression and controls enabled us to investigate whether cognitive impairment persists beyond episodes of low mood in depression.

Results

Our meta-analysis revealed significant moderate cognitive deficits in executive function, memory and attention in patients with depression relative to controls (Cohen's d effect sizes ranging from −0.34 to −0.65). Significant moderate deficits in executive function and attention (Cohen's d ranging from −0.52 to −0.61) and non-significant small/moderate deficits in memory (Cohen's d ranging from −0.22 to −0.54) were found to persist in patients whose depressive symptoms had remitted, indicating that cognitive impairment occurs separately from episodes of low mood in depression.

Conclusions

Both low mood and cognitive impairment are associated with poor psychosocial functioning. Therefore, we argue that remediation of cognitive impairment and alleviation of depressive symptoms each play an important role in improving outcome for patients with depression. In conclusion, this systematic review and meta-analysis demonstrates that cognitive impairment represents a core feature of depression that cannot be considered an epiphenomenon that is entirely secondary to symptoms of low mood and that may be a valuable target for future interventions.

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Most cited references 8

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Cambridge Neuropsychological Test Automated Battery (CANTAB): A Factor Analytic Study of a Large Sample of Normal Elderly Volunteers

T.W. Robbins, M. James, A.M. Owen … (1994)

The CANTAB battery was administered to a large group (n = 787) of elderly volunteers in the age range from 55 to 80 years. This battery, which is based on tests used to identify the neural substrates of learning and memory in non-human primates, has now been extensively used in the assessment of various forms of dementia and also validated on patients with neurosurgical lesions of the frontal and temporal lobes. The tests employed were pattern and spatial recognition, simultaneous and delayed matching to sample, learning of visuo-spatial paired associates, a matching to sample, reaction time task and a test of spatial working memory. The sample was banded into different IQ bands based on performance on 5 standard tests of intelligence. The MMSE was also administered to exclude cases of possible dementia (n = 16) in the normal sample. In general, performance declined with age and IQ, but these factors did not interact. A factor analysis (with varimax rotation) identified 4 factors with eigenvalues greater than 1, which accounted for over 60% of the variance. Factor 1 was equated with general learning and memory ability and loaded significantly with the Intelligence scores; factor 2 was related to speed of responding and loaded most heavily with Age. Comparisons were also made of performance on CANTAB of those subjects with dementing scores on the MMSE and the lowest 5th percentile of the population sample. The results are discussed in terms of the utility of the CANTAB battery for the assessment of dementia and of the implications for theories of changes in cognitive function during normal aging.

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Socioeconomic burden of subsyndromal depressive symptoms and major depression in a sample of the general population.

Nancy Judd, Yannis Paulus, J Rapaport … (1996)

The authors' goal was to evaluate the association between impairment in daily function and subsyndromal depressive symptoms as well as major depression to determine the economic and societal significance of these conditions. Using 12-month prevalence data gathered by the National Institute of Mental Health (NIMH) Epidemiologic Catchment Area Program (ECA), based on responses to the NIMH Diagnostic Interview Schedule, the authors divided the 2,393 subjects from the Los Angeles ECA site into three groups: subjects with subsyndromal depressive symptoms (N = 270), major depression (N = 102), and no depressive disorder or symptoms (N = 2,021). The groups were compared on 10 domains of functional outcome and well-being. Significantly more subjects with depressive symptoms than subjects who had no disorder reported high levels of household strain, social irritability, and financial strain as well as limitations in physical or job functioning, restricted activity days, bed days, and poor health status. Significantly more subjects with major depression than subjects with no disorder reported major financial losses, bed days, high levels of financial strain, limitations in physical or job functioning, and poor health status. Except for lower self-ratings of health status, no significant differences were found between subjects with subsyndromal symptoms and those with major depression. Significantly more people with subsyndromal depressive symptoms or major depression reported impairment in eight of 10 functional domains than did subjects with no disorder. The high 1-year prevalence of subsyndromal depressive symptoms, combined with the associated functional impairment, emphasizes the clinical and public health importance and need for additional investigations into these symptoms.

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On the nature and pattern of neurocognitive function in major depressive disorder.

Emma Leach, K. Zakzanis, Matthew E Kaplan (1998)

An effect size analysis of neurocognitive function in patients with major depressive disorder using meta-analytic principles was conducted. The results from 726 patients with depression and 795 healthy normal controls revealed that depression had the largest effect on measures of encoding and retrieval from episodic memory. Intermediate effect sizes were recorded on tests of psychomotor speed and tests that require sustained attention. Minimal effect sizes were found on tests of semantic memory, primary memory, and working memory. Moreover, major depressive disorder is accompanied by dysfunction of effortful encoding of information along with an accompanying inefficiency of retrieving poorly encoded information from declarative memory.