Cognitive control in late-life depression: response inhibition deficits and dysfunction of the anterior cingulate cortex.

OBJECTIVES: Geriatric depression is associated with frontolimbic functional deficits, and this frontal dysfunction may underlie the marked executive control deficits often seen in this population. The authors' goal was to assess the integrity of frontal cortical functioning in geriatric depression, while these individuals performed a standard cognitive control task. The N2 component of the event-related potential (ERP), an evoked response generated within the anterior cingulate cortex (ACC), is significantly enhanced when nondepressed individuals successfully inhibit a response, providing an excellent metric of frontal inhibitory function.
DESIGN: The authors used a variant of a demanding Go/NoGo task-switching paradigm that required participants to inhibit response execution during NoGo trials by overcoming a potent response tendency established by frequent Go trials. PARTICIPANTS: The authors compared a cohort of depressed geriatric outpatients (N = 11) with a similarly aged group of nondepressed participants (N = 11). MEASUREMENTS: Reaction times, accuracy, and high-density event-related potential recordings from a 64-channel electrode montage were obtained.
RESULTS: A significantly enhanced N2 to NoGo trials was observed in nondepressed elderly participants, with generators localized to the ACC. In contrast, this enhancement was strongly reduced in the depressed sample. Source analysis and topographic mapping pointed to a displacement of N2 generators toward more posterior areas of the middle frontal gyrus in depressed subjects.
CONCLUSIONS: Findings confirm previous reports of an inhibitory control deficit in depressed elderly who show significantly increased rates of commission errors (i.e., failures to inhibit responses on NoGo trials). Electrophysiologic data suggest underlying dysfunction in ACC as the basis for this deficit.