Memory functioning in depression : Empirical evidence for episodic memory impairments, possible causes, and suggested risk factors

Abstract

Depressive disorders are amongst the most widespread mental health issues that can lead to a reduced quality of life. Even though depression is commonly known to be a disorder of affect, it is often accompanied by various difficulties with cognitive functions such as memory-related impairments as well. However, inconsistent empirical findings of previous investigations still lead to a lack of clarity regarding cognitive functioning in depression. Therefore, the major aim of the present doctoral thesis was to assess and explore memory-related functioning in clinically depressed patients compared to healthy individuals using the Wechsler Memory Scale in its recent edition (WMS-IV). Particularly, the main purpose was to clarify whether depression is associated with severe episodic memory impairments and if certain characteristics of depressed individuals might explain such cognitive deficits. In Study I, age and gender could be shown to exert a general effect on certain components of episodic memory. As a major prerequisite for all subsequent analyses, Study II confirmed that the WMS-IV test battery for the most part provides suitable neuropsychological measures for the purpose of comparing test performances of depressed patients with those of healthy controls. In line with preliminary expectations, episodic memory performances turned out to be significantly lower for depressed patients than for healthy controls in Study III. The findings additionally supported the assumption that depression-related impairments in episodic memory might be partially explained by certain executive dysfunctions in depression. Study IV further emphasized the role of disorder subtypes for explaining cognitive dysfunctions as patients with recurrent depressive episodes were found to feature even lower WMS-IV test performances than patients with their first depressive episode. Finally, these findings were extended by examining certain factors that might possibly contribute to the development of episodic memory impairments in depression. Besides the general effects of age, gender, and education, the findings of Study V further suggested that especially those patients that are affected by higher levels of depression severity, longer illness durations, or by more depressive episodes than other depressed patients are at greater risk to develop more severe memory-related impairments in the course of the disorder. In due consideration of several methodological strengths and limitations, the findings of the present research studies and their implications for future research and clinical practice are discussed at the end of this thesis.