Abstract
Normal aging and depression both slow information processing speed which leads to poorer attentional control, shallower inhibition monitoring, poorer encoding, poorer updating of short term memory, and subsequent poorer learning, set-shifting, error monitoring, inhibition control, and cognitive planning. A combination of aging and depression amplifies these cognitive effects. Deterioration in frontal brain functioning in normal aging is irreversible, but altering of frontal brain function due to depression may be reversible. Since the symptoms are indistinguishable, it is difficult to separate effects of depression and aging with use of neuropsychological tests, even when premorbid history is known. Statistical group effects show more severe cognitive effects in late life depression than in normal aging or depression in younger persons, but no particular cognitive markers of depression in older subjects have been identified. Attention and inhibition are closely related, but their relationship needs to be studied further. It is not clear, whether a problem with inhibition of irrelevant stimuli occurs because of attentional deficits due to late life depression, or if it is a primary consequence of the depression. Further studies on the relationship between inhibition, attention and processing speed involving homogeneous depressed and non-depressed groups of different age may help disentangle this relationship.
Highlights
Previous literature has suggested that cognitive functions are affected in depression and that cognitive decline due to depression may be permanent or lasting, even when the patient enters a euthymic stage [1]
This literature review points to information processing speed as the common factor that may explain most of the cognitive decline found in depression, and depression in old age in particular, since normal aging causes slower information processing speed
As depression affect brain function in areas involved in attention and executive control, at least on a temporary basis [6] it may be that this changing of brain activity pattern can lead to a permanent or lasting effects on cognitive functioning
Summary
Previous literature has suggested that cognitive functions are affected in depression and that cognitive decline due to depression may be permanent or lasting, even when the patient enters a euthymic stage [1]. (2014) Cognitive Effects of Late Life Depression: Review of Neuropsychological Findings. Story et al [3] included attention and processing speed in their definition of executive functions, since these functions rely on prefrontal and subcortical brain-structures. This approach makes it difficult to assess which of the underlying cognitive sub-functions are directly affected by the depressed state and which are affected because of dependencies of interconnected cognitive sub-functions. We review the current literature with focus on practical application rather than theoretical framework, and investigate which cognitive sub-functions are directly or indirectly affected by depression. The search was repeated without the aging terms in order to identify the most referred articles on neuropsychological findings on depression
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