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. Our 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 non-depressed individuals successfully inhibit a response, providing an excellent metric of frontal inhibitory function.
Design
We 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
We compared a cohort of depressed geriatric outpatients (n=11) with a similarly aged group of non-depressed participants (n=11).
Measurements
Reaction times, accuracy and high-density ERP recordings from a 64-channel electrode montage were obtained.
Results
A significantly enhanced N2 to NoGo trials was observed in non-depressed 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 towards 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). Electrophysiological data suggest underlying dysfunction in ACC as the basis for this deficit.