ABNORMAL NEURAL RESPONSE TO FEEDBACK ON PLANNING AND GUESSING TASKS IN PATIENTS WITH UNIPOLAR DEPRESSION

Background. It has been suggested that patients with unipolar depressi on show abnormal responses to negative feedback in the performance of cognitive tasks. Positron emission tomography (PET) has previously ide ntified blood flow abnormalities in depressed patients during cognitiv e performance. We have also used PET to identify regions where there i s differential neural response to performance feedback in normal volun teers. In this study we aimed to test the hypothesis that blood flow i n these regions, the medial caudate and ventromedial prefrontal cortex , would be abnormal in depressed patients. Methods. Six patients with unipolar depression and six matched controls were scanned using PET wh ile performing cognitive tasks in the presence and absence of feedback . Results. Compared with controls, depressed patients failed to show s ignificant activation in the medial caudate and ventromedial orbitofro ntal cortex. Blood flow was lower and a differential response, observe d in normals, under different task and feedback conditions was not see n in the patients. Discussion. The findings suggest that the behaviour al response to feedback in depressed patients is associated with an ab normal neural response within the medial caudate and ventromedial orbi tofrontal cortex, regions implicated in reward mechanisms. We argue th at the observed abnormalities may depend on a combination of psycholog ical factors, with both cognitive and emotive components.