Delay discounting and task performance consistency in patients with schizophrenia.

To study impaired goal-oriented behavior in schizophrenia (SZ), we used a delay discounting task, which consists of a series of choices between receiving a small immediate or larger delayed reward. Few studies of delay discounting have evaluated response consistency (R(2)), which is especially relevant in SZ because of documented inconsistency in task performance. We calculated the rate of discounting (k) and R(2) in SZ (n=35) and healthy controls (HC; n=21). Using a criterion value of R(2)>0.60 to define consistent performance allowed us to compare discounting in consistent SZ and HC, as well as in inconsistent SZ. Groups did not differ significantly in smoking. Compared to HC, consistent SZ showed greater delay discounting. Both groups exhibited similar patterns of decreasing immediate choices across trial categories, although the decrease was less for SZ. Separate analyses on smokers and non-smokers showed that this group difference was carried by the non-smokers. Inconsistent SZ discounted more than HC and consistent SZ, but their aberrant pattern of choices casts doubt on the validity of their calculated k values.

An fMRI investigation of delay discounting in patients with schizophrenia.

Schizophrenia (SZ) is associated with a reduced ability to set meaningful goals to reach desired outcomes. The delay-discounting (DD) task, in which one chooses between sooner smaller and later larger rewards, has proven useful in revealing executive function and reward deficits in various clinical groups. We used fMRI in patients with SZ and healthy controls (HC) to compare brain activation during performance of a DD task. Prior to the neuroimaging session, we obtained each participant's rate of DD, k, on a DD task and used it to select a version of the DD task for each participant's fMRI session. Because of the importance of comparing fMRI results from groups matched on performance, we used a criterion value of R (2) > 0.60 for response consistency on the DD task to analyze fMRI activation to DD task versus control trials from consistent SZ (n = 14) and consistent HC (n = 14). We also compared activation between the groups on contrasts related to trial difficulty. Finally, we contrasted the inconsistent SZ (n = 9) with the consistent HC and consistent SZ; these results should be interpreted with caution because of inconsistent SZ's aberrant performance on the task. Compared with consistent HC, consistent SZ showed reduced activation to DD task versus control trials in executive function and reward areas. In contrast, consistent SZ showed more activation in the precuneus and posterior cingulate, regions of the default mode network (DMN) that are typically deactivated during tasks, and in the insula, a region linked to emotional processing. Furthermore, consistent SZ had abnormal activation of lateral and medial frontal regions in relation to trial difficulty. These results point to disruption of several neural networks during decision making, including the executive, reward, default mode, and emotional networks, and suggest processes that are impaired during decision making in schizophrenia.