The behavioral effects of lesions of the prelimbic cortex (PL), mediodorsal nucleus of the thalamus (MD), and anterior thalamic nuclei (ANT) were investigated in 2 attentional tasks in rats: the 5-choice serial reaction time task and a vigilance task. Although there was no lesion effect on accuracy in the 5-choice task, PL lesions enhanced perseverative responding during baseline performance and when stimulus duration was reduced. In contrast, MD lesions increased premature responding during baseline performance and when the intertrial interval was varied unpredictably. In the vigilance paradigm, PL lesions also impaired rats' ability to detect the light signal at baseline and at the reduced stimulus duration. ANT lesions did not substantially disrupt performance. The results suggest that different aspects of attention may be attributable to the PL and the MD and that the mechanisms underlying inhibitory control of behavior may be attributable to functionally different thalamocortical circuits.