Abstract
Purpose :
Caffeine is the most common neurostimulator, with an average daily consumption of 165 mg in the US. Caffeine is known to affect central nervous system processing through an antagonistic mechanism at certain adenosine receptors leading to an upregulation of dopamine which causes increases awareness and enhanced motor and sensory behavior. Through a double-blinded prospective study, we investigated whether caffeine alters the phosphene threshold, a marker of visual cortex excitability.
Methods :
18 participants with normal vision were randomly assigned to the caffeine and placebo groups. The participants in the caffeine group were given a 200 mg caffeine pill, while those in the placebo group received a similar-looking rice flour pill. In the preliminary baseline session, phosphene thresholds were measured using a single-pulse transcranial magnetic stimulation (TMS) on the occipital cortex (primary visual cortex). Neuronavigation-guided TMS coil was placed at 3 cm above the inion and was moved across a 1 x 1 cm2 grid to locate the "hotspot" that elicits phosphene with minimal stimulation strength. The hotspot was then marked on the Brainsight software of the neuronavigation unit. 6 of 9 participants in the caffeine group and 5 of 9 participants in the placebo group successfully detected phosphene and continued with the study. Caffeine/placebo pills were administered, and the participants watched a show on Disney for 45 mins. The phosphene thresholds were remeasured at the previously marked hotspot, 45 mins post-caffeine intake to look for any effect of caffeine.
Results :
Post-intervention, none of the participants, in either caffeine (pre-intervention: 48 ± 6%, post-intervention: 44 ± 7%, p = 0.44) or the placebo (pre-intervention: 49 ± 6%, post-intervention: 48 ± 7%, p = 0.85) groups, showed any significant change in phosphene threshold.
Conclusions :
Our results indicate that caffeine does not alter neuronal excitability within the primary visual cortex. However, our study does not establish a dose-response relationship between caffeine and phosphene threshold. In addition, further studies are warranted to understand the effect of caffeine on the behavioral vision that is processed within the primary visual cortex.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.