Plain language summary
Impairments in goal-directed attention are a frequent problem in older adults but these problems become magnified in neurodegenerative conditions like Parkinson's disease (PD). Although symptomatic treatment of PD focuses on motor deficits, cognitive deficits can be disabling, even in the early stages. This study is a single-blind, cross-over trial which compared the effect of a tablet containing 100-mg caffeine (Proplus) which was dissolved in instant decaffeinated coffee. Twenty-four PD patients and forty-four aged matched healthy elderly participants (controls) were enrolled in the study. Results show that caffeine: - did not affect attention in a unitary manner, across all attentional networks. In fact, the effect of caffeine on cognitive performance depended greatly upon the specific task requirements. - improved accuracy on the choice reaction time task. - improved accuracy of response selection in both the congruent and incongruent conditions. Authors conclude that caffeine’s overall attentional effects put forward by their study should be considered neither exclusively positive nor detrimental but instead conditional on task demands.
Abstract
INTRODUCTION Caffeine is frequently consumed to boost goal-directed attention. These procognitive effects may occur due to the adenosine-mediated enhancement of monoamines, such as dopamine, after caffeine administration. As such, caffeine's beneficial effects may be altered in conditions such as Parkinson's disease (PD). However, whether caffeine improves cognition, and at what cost, has not been experimentally established in patients with neurodegenerative disease. METHODS Single-dose trials to probe cognitive effects of caffeine are often confounded by short-term caffeine abstinence which conflates caffeine's effects with treatment of withdrawal. Using a placebo controlled, blinded, randomised trial design, we assessed the effect of 100 mg of caffeine across well-established tasks (Choice reaction time, Stroop Task and Rapid Serial Visual Presentation Task; RSVP) that probe different aspects of attention in PD patients (n = 24) and controls (n = 44). Critically, participants withdrew from caffeine for a week prior to testing to eliminate the possibility that withdrawal reversal explained any cognitive benefit. RESULTS Caffeine administration was found to reduce the overall number of errors in patients and controls on the Stroop (p = .018, η2p = .086) and Choice reaction time (p < . 0001, η2p = .588) tasks, but there was no specific effect of caffeine on ignoring irrelevant information in the Stroop task. On the RSVP task, caffeine improved dual item accuracy (p = .037) but impaired single item accuracy (p = .044). Across all tasks, there was little evidence that caffeine has different effects in PD participants and controls. CONCLUSION When removing withdrawal effects as a factor, we demonstrate caffeine has beneficial effects on selective attention but is a double-edge sword for visual temporal attention and would need careful targeting to be clinically useful.
