Event-Related Brain Potentials in Depression : Clinical , Cognitive and Neurophysiologic Implications

Individuals having a depressive disorder commonly experience difficulties in concentration, attention and other cognitive functions, such as memory and executive control (Austin et al., 2001; Porter et al., 2003). The recording of event-related brain potentials (ERPs) provides a noninvasive means for studying cognitive deficits in depressive disorders and their underlying neurophysiologic mechanisms. The precise temporal resolution of ERPs can reveal unique information about the specific stage of processing that may lead to disruption of performance on cognitive tasks, e.g., early sensory/attentional processing as reflected in the N1 potential or later cognitive evaluation as reflected in the P3 potential. Moreover, ERPs can provide noninvasive biological markers for assessing treatment effects and, most promisingly, for determining who will benefit from a particular course of treatment. By far, the largest number of ERP studies of depression have focused on the cognitive P3 potential during target detection “oddball” tasks. We will review the findings of these studies and focus on recent studies that examined P3 subcomponents, which provide new evidence concerning specific cognitive operations that may be disturbed in depression. After reviewing these findings, we will examine ERP findings in depressed patients obtained during more challenging cognitive paradigms, including more demanding auditory or visual discrimination tasks. We will also review studies that have recorded ERPs in depressed patients during recognition memory tasks, which provide information on ERP correlates of episodic memory. Surprisingly few studies have measured ERPs of depressed patients during processing of emotional stimuli, and yet, such data may have particular relevance to mood disorders and will therefore be reviewed. A number of recent studies in depressed patients have found abnormalities of negative brain potentials associated with monitoring of cognitive performance, e.g., error-related negativity (ERN). These studies, as well as others measuring the intensity-dependency of auditory N1-P2 potentials, will be highlighted because they suggest the potential value of these ERP measures for predicting clinical response to antidepressants. One aim of this review is therefore to bring together the findings of studies measuring ERPs in depressed patients during a variety of sensory, cognitive and emotional tasks, so as to contribute toward a better understanding of the specific processes and neurophysiologic mechanisms that are dysfunctional in depressive disorders. For instance, evidence of ERP abnormalities related to attentional or cognitive control processes are suggestive of deficits involving frontal or anterior cingulate cortex. Another aim is to highlight the clinical relevance of ERP findings in depressed patients by pointing to the relation of the patients’ ERPs to their clinical features, most notably severity of depressive symptoms, diagnostic subtype, and therapeutic response to treatments. From a more methodological perspective, we will present new findings illustrating the power of combining current-source density (CSD) and principal components analysis (PCA) techniques, which take better advantage of both the temporal resolution of ERPs and the spatial resolution of dense electrode arrays than traditional analysis methods of reference-dependent surface potentials (Kayser & Tenke, 2006a,b).