The Impact of Caffeine on Cognition in Schizophrenia

Caffeine is the most used psychoactive drug in Canada, with regular consumption by 88% of the adult population, While rates of caffeine consumption are considered to be high in the general population, there is some evidence that they may be even higher within schizophrenia patients; in a 2006 U.S. study, daily consumption rates of caffeine were nearly double those observed in a healthy control population (471.6 mg/day vs. 254.2 mg/day). Furthermore, 13% of the schizophrenia population studied ingested more than 1000 mg/day of caffeine, well above the 400 mg daily maximum recommended by Health Canada. High doses of caffeine are particularly concerning for individuals with schizophrenia; caffeine alters dopaminergic activity at post-synaptic neurons through its actions at adenosine A2A receptors, which may exacerbate positive symptoms, such as delusions and hallucination. This significant rate of consumption is likely due in part to caffeine's actions on the human brain, resulting in increased arousal, elevated mood and beneficial effects on a wide-range of cognitive processes including verbal working memory, sustained attention, and executive function. These areas of caffeine-induced cognitive improvement notably overlap with the cognitive domains that are reported to be diminished in schizophrenia. Despite this overlap and the rates of caffeine consumption observed within schizophrenia, research reports examining the effects of caffeine on cognition and brain activity are all but non-existent in this population. The primary objective of this proposal is to compare the effects of caffeine and placebo on brain function during cognitive tasks in participants with schizophrenia. While the investigators have specific hypotheses for each task, overall the investigators hypothesize that caffeine will improve cognitive function (as evidenced by larger ERP amplitudes and/or reduced ERP latencies) compared to placebo in schizophrenia patients, with similar effects (albeit reduced in magnitude) observed in non-patient healthy controls.