Abstract
Cognitive control – a system that modulates the operation of other cognitive in the service of goal-directed behavior – is a core deficit in schizophrenia and its association with frontal cortical gamma oscillatory disturbances suggests a way to integrate molecular findings and models of cognition. Here we present data from first episode patients and address the role of concurrent cannabis usage in cognitive control impairments and its neurophysiological markers. 62 healthy controls were compared to 101 first episode patients performing the Preparing to Overcome Prepotency (POP) task, a cued stimulus-response reversal task, which in chronic schizophrenia patients, has been shown reduced engagement of prefrontal gamma activity. Psychosis subjects included patients with schizophrenia, schizoaffective disorder as well as other psychosis spectrum disorders, and had a variable history of cannabis usage. Patients showed impaired performance and complex spectral alterations of EEG activity. This included reduction of gamma activity in the frontal electrodes during high-control trials. However in the patient group, significant variability was explained by cannabis usage history. In particular a greater gamma power impairment was observed for subjects who had greater lifetime cannabis usage and heavy earlier cannabis use (<16 years old) appeared to exert a more deleterious effect than later use or more minimal use. The findings of this study suggest that the presence and time course of cannabis use history in first episode psychosis has a significant deleterious impact on frontal cortical gamma oscillations in the context of a cognitive control task. Cannabis effects during development are recognized as a critical area in psychosis research, possibly implicated in the genesis, presentation of the disorder and/or serving as an important confounding factor. The present data highlights how the development of specific and accurate models of cognitive impairment in psychosis needs to address and be informed by complex interactions with cannabis usage.