The anterior cingulate cortex (ACC) participates in both performance optimization and evaluation, with dissociable contributions from dorsal (dACC) and rostral (rACC) regions. Deactivation in rACC and other default-mode regions is important for performance optimization, whereas increased rACC and dACC activation contributes to performance evaluation. Errors activate both rACC and dACC. We propose that this activation reflects differential errorrelated involvement of rACC and dACC during both performance optimization and evaluation, and that these two processes can be distinguished by the timing of their occurrence within a trial. We compared correct and error antisaccade trials. We expected errors to correlate with an early failure of rACC deactivation and increased activation of both rACC and dACC later in the trial. Eighteen healthy subjects performed a series of prosaccade and antisaccade trials during event-related functional MRI. We estimated the hemodynamic responses for error and correct antisaccades using a finite impulse-response model. We examined ACC activity by comparing error and correct antisaccades with a fixation baseline and error to correct antisaccades directly. Compared with correct antisaccades, errors were characterized by an early bilateral failure of deactivation of rACC and other default-mode regions. This difference was significant in rACC. Errors also were associated with increased activity in both rACC and dACC later in the trial. These results show that accurate performance involves deactivation of the rACC and other default mode regions and suggest that both rACC and dACC contribute to the evaluation of error responses.default-mode network ͉ performance evaluation ͉ task-induced deactivation ͉ inhibition ͉ cognition E lectrophysiological and neuroimaging studies consistently report anterior cingulate cortex (ACC) activity during error commission (1-5). The ACC, however, is a heterogeneous structure that can be parsed into dorsal (dACC) and rostral (rACC) regions based on cytoarchitecture, function, and connectivity (6-9). The dACC extends caudally from the genu of the corpus callosum to the vertical plane of the anterior commissure and connects with the lateral prefrontal cortex and hippocampus to regulate effortful cognitive operations. The rACC lies anterior and ventral to the genu of the corpus callosum and forms a circuit with the amygdala, insula, and ventral striatum to oversee emotional processing (for review, see ref. 10). Given these specializations, it is likely that the dACC and rACC make different contributions during error commission. In the present study, we examined activity in both these regions during different phases of error commission.Error-related activity in both rACC and dACC is thought to reflect their contributions to performance evaluation (2, 5, 11). The dACC is believed to be the primary generator of the error-related negativity (ERN) (5, 12), an event-related potential occurring 80-180 ms post-error (13), although a generator in the medial prefrontal cor...