Dysfunction of frontal cortex, and particularly the ACC, has been reported in depressed patients using imaging techniques (Bremner, Vythilingam, Vermetten, Vaccarino, & Charney, 2004; Drevets et al., 1997; Siegle, Steinhauer, & Thase, 2004), consistent with an attentional impairment. However, a similarity between P3a and no-go P3 produced in a go/no-go task (Polich, 2007) suggests the possibility that parallel findings in novelty oddball and executive control paradigms may result from common neuroanatomical mechanisms that underlie attentional control, response selection, and/or response inhibition. The present findings of an early source reduction in depression for novels (i.e., responses correctly inhibited) may thereby be related to the reported no-go performance decrement in depression (Kaiser et al., 2003) and to a reduction in no-go P3 (Ruchsow et al., 2008). If the early central novelty source actually reflects inhibition of a task-specific response to irrelevant stimuli, it would suggest that a motor, rather than an attentional, process is impaired in depression. However, inhibition in the novelty oddball task could extend well beyond the task-specific behavioral response, to encompass autonomic/affective aspects of the orienting response as well.
