Negative symptoms are associated with an increased subjective cost of cognitive effort

Motivational deficits in schizophrenia are proposed to be attributable in part to abnormal effort-cost computations. Inflated subjective cognitive effort costs may explain diminished functioning in schizophrenia to the extent that they drive avoidance of complex decision-making and planning. Although previous data support inflated subjective physical effort costs for individuals with schizophrenia, evidence on cognitive effort is mixed. We exploited the methodological advantages of a recently developed cognitive effort-discounting paradigm (Westbrook, Kester, & Braver, 2013) to examine effort-cost computations in schizophrenia. The paradigm quantifies subjective costs in terms of explicit, continuous discounting of monetary rewards based on parametrically varied demands (levels N of the N-back working memory task), holding objective features of task duration and reward likelihood constant. Both healthy participants (N = 25) and schizophrenia patients (N = 25) showed systematic influences of reward and task demands on choice patterns. Critically, however, participants with schizophrenia discounted rewards more steeply as a function of effort, indicating that effort was more costly for this group. Moreover, discounting varied robustly with symptomatology, such that schizophrenia patients with greater clinically rated negative symptom severity discounted rewards more steeply. These findings extend the current literature on abnormal-effort cost computations in schizophrenia by establishing a clear relationship between the costliness of cognitive effort and negative symptoms.