Explicit and Implicit Memory in Late-Life Depression

Objective: Late-life depression has been associated with memory loss and is frequently assumed to be a risk factor for continued cognitive decline. This study examined cognition in patients with late-life depression with a focus on the assessment of the extent and type of memory loss among elderly depressed patients. Methods: Two-year cross-sectional study of elderly depressed (N = 112) and nondepressed (N = 138) individuals at or older than 60 years in an urban area surrounding a major medical center in southern California. Participants had little to moderate stroke risk. Volunteers were screened with the Hamilton Depression Rating Scale and the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) Axis I Disorders. Patients were diagnosed for major depression by a geriatric psychiatrist using DSM-IV criteria. Volunteers completed neuropsychological testing, a standard battery of laboratory tests, and a neurologic and psychiatric evaluation to rule out a medical burden that might contribute to depression or early dementia. Results: Depressed patients showed deficits in attention and processing, executive function, and immediate explicit recall. Implicit learning and episodic recall of the testing procedure, semantic and phonetic fluency, and retention of newly acquired verbal material after a delay period were comparable with controls. Conclusion: Moderately depressed patients demonstrate a pattern of cognitive deficits suggestive of mild frontal dysfunction during recall tasks. Their retention of material over a delay period and their intact language skills indicate medial hippocampal function similar to controls. Subcortically mediated implicit memory is also at normal levels. These findings support current efforts to identify pathways of frontal and/or striatal compromise during depressive episodes. (Am J Geriatr Psychiatry 2011; 19:364-373)