Background:
The cerebral activation changes associated with the overlapping cognitive features of cannabis use and schizophrenia have not been systematically studied. The Tower of London Task (TOL) was used to assess functional brain activation in these two groups and in comorbid first-episode schizophrenia and cannabis users.
Methods:
Event-related functional magnetic resonance imaging measured cerebral activation during the TOL task in 12 patients with first-episode schizophrenia, 17 recently abstinent long-term cannabis users, 7 recently abstinent cannabis using patients with schizophrenia and 17 healthy subjects. A two-stage random-effects analysis was used to model the BOLD response to assess cortical activation as a function of increasing task difficulty and to assess for the main effect of each diagnosis.
Results:
We found prefrontal activation defi cits in patients with schizophrenia that overlapped with cannabis users. A statistical trend in the comorbid subjects for reduced BOLD activation in the left superior parietal lobule and prefrontal cortices was observed. The diagnosis of schizophrenia largely accounted for the prefrontal deficit, while a history of heavy cannabis use associated with increased BOLD activation in the visual cortex.
Conclusions:
There were common deficits in activation of the dorsolateral prefrontal cortex to the most difficult tasks. Ancillary brain regions were recruited, possibly to subserve the demands of complex TOL tasks. The combination of cannabis use and schizophrenia may exert a synergistic effect on altering frontal lobe recruitment during high-demand cognitive tasks.
