Temporal processing in schizophrenia: effects of task-difficulty on behavioral discrimination and neuronal responses.

Deficits in temporal judgment in schizophrenia have been observed in behavioral and electrophysiological studies for years. The functional neuroanatomy of temporal judgment in schizophrenia is, however, poorly understood. Recent neurophysiological research suggests that timing deficits in this population may not be widespread across all timing tasks, but specifically associated with high levels of difficulty. We evaluated differences between individuals with schizophrenia (N=16) and healthy subjects (N=18) during a temporal discrimination task at two levels of difficulty. Subjects were studied with functional magnetic resonance imaging (fMRI) at 3T while discriminating tone durations. Behaviorally, the schizophrenia group performed worse than the control group at both levels of difficulty. Similarly, group differences in patterns of brain activation were observed across both difficulty conditions. In the easy condition, individuals with schizophrenia showed less activation in the supplementary motor area and insula/opercula, regions known to be involved in temporal processing. These group differences increased in the difficult condition. In addition, the striatum was less active in individuals with schizophrenia in the difficult condition. Comparing the difficult to easy conditions revealed robust differences in the bilateral striatum and the insula/opercula, suggesting that the striatum plays a key role in temporal processing deficits in schizophrenia, especially under difficult conditions. These observations suggest that temporal judgment deficits reflect widespread neuroanatomical network involvement in schizophrenia, some of which are not directly related to task difficulty. These findings shed light on disparate findings in the timing literature regarding the role of task difficulty in temporal judgment deficits in schizophrenia.