Evidence for continuing neuropsychological impairments in depression

Abstract

Background: Neuropsychological deficits have been reported in patients with major depressive disorder (MDD) during an acute episode of MDD. Little is known whether these abnormalities persist when patients are remitted. The purpose of the present study was to describe the neuropsychological functioning of fully remitted, unmedicated patients with a history of MDD by focusing on tasks related to prefrontal cortex functioning. Methods: Twenty-eight young to middle-aged, unmedicated, fully remitted patients with MDD were compared to 23 healthy control subjects on tasks from the Cambridge Automated Neuropsychological Test Battery (CANTAB) and the California Verbal Learning Test (CVLT). Results: Patients with remitted MDD relative to controls were impaired on tasks of rapid visual information processing (RVIP), psychomotor performance and spatial working memory (SWM). After correction for residual depressive symptoms, deficits in sustained attention remained significant. Limitations: CANTAB tasks are not equated for difficulty, and difficulty differences between the CANTAB tasks and the CVLT are not known. Conclusions: These findings suggest deficits in sustained attention as vulnerability marker for MDD. The functional importance of this finding and the neuronal networks involved remain to be elucidated.

Introduction

During the past few years, there has been interest in cognitive impairments in recurrent major depressive disorder (MDD) as reflected in the increasing number of studies, which characterize neuropsychological deficits in this population. So far, these studies have exclusively involved patients during the acute phase of MDD, and the results suggest that MDD is associated with cognitive deficits in domains of psychomotor speed (Sobin and Sackeim, 1997), memory Burt et al., 1995, Cohen et al., 1982, Golinkoff and Sweeney, 1989, sustained attention (Cornblatt et al., 1989), and executive functioning in domains including memory and complex problem solving Merriam et al., 1999, Sweeney et al., 1998. However, thus far, in MDD patients, a consistent and specific profile of neuropsychological abnormalities has not been established. Clinical correlates of cognitive deficits in MDD include symptom severity with more pronounced depressive symptoms associated with more prominent cognitive dysfunction Albus et al., 1996, Grant et al., 2001, Landro et al., 2001, melancholic features (Austin et al., 1999), and age with more abnormalities found in elderly patients relative to younger MDD patients Beats et al., 1996, Grant et al., 2001, Nelson et al., 1998, Sweeney et al., 2000. Moreover, it remains unclear whether cognitive disturbances persist beyond the symptomatic phase of MDD. The aim of the present study was to compare neuropsychological functions between groups of young to middle-aged, unmedicated, remitted patients with unipolar MDD and healthy controls. Based on previous studies about cognitive impairments in symptomatic depressed, untreated MDD patients, we tested the hypothesis that these deficits are characteristic for MDD and expected impairments on psychomotor performance, executive functions, memory, and sustained attention in the remitted MDD patients relative to healthy controls.