Caffeine improves contrast sensitivity of freely moving rats.

Caffeine (1, 3, 7-trimethylxanthine) is a well-known central nervous system stimulant that affects various brain functions such as attention, memory and sensation. However, it remains unclear whether and how caffeine modulates visual ability such as contrast sensitivity (CS) and the CS-spatial frequency (SF) relationship. To investigate these points, we tested the effects of caffeine on the perceptual CS of rats under three SF conditions. CS was measured using a two-alternative forced choice (2AFC) grating detection task combined with a staircase method. Intraperitoneal administration of caffeine 30 min prior to the task improved CS in an SF-dependent manner, in which the improving effect was observed at 0.1 cycles/degree (cpd) of the optimal SF for rats but not at 0.5 or 1 cpd. We concluded that caffeine, a representative ingredient contained in foods or drinks consumed daily, leads to an improvement of perceptual visual sensitivity.