Scientists have shown that a single exposure to blue wavelength light for a period of approximately one-half hour leads to measurable changes in brain activity in the prefrontal cortex when people engage in a cognitive task, even after light exposure is terminated.

Researchers at the University of Arizona studied 35 healthy adults between the ages of 18 and 32. The participants were randomized to receive a 30-minute exposure to either blue (active) or amber (placebo) light, followed immediately by functional magnetic resonance imaging (fMRI) while undertaking a working memory task.

Participants receiving the blue light were faster in their responses during the memory task and showed increased activation in the dorsolateral  prefrontal cortex (DLPFC) and ventrolateral (VLPFC) prefrontal cortex, compared with participants in the amber light group. Further, greater activation within the VLPFC was correlated with faster working memory response times.

The findings suggest that a short single exposure to blue light is sufficient to produce measurable changes within the DLPFC and VLPFC, leading to faster reaction times and more efficient responses during conditions of greater cognitive load. These findings may have important implications for using blue light as a tool to increase alertness and response times in a variety of work settings, such as cockpits, operating rooms and in military settings.

"Previous studies only focused on the effects of light during the period of exposure. Our study adds to this research by showing that these beneficial effects of blue wavelength light may outlast the exposure period by over 40 minutes," said Anna Alkozei, postdoctoral fellow at the University of Arizona.

“Importantly, our findings suggest that using blue light before having to engage in important cognitive processes may still impact cognitive functioning for over half an hour after the exposure period ended. This may be valuable in a wide range of situations where acute blue light exposure is not a feasible option, such as testing situations,” said Alkozei.

"These findings are important as they link the acute behavioral effects of blue light to enhanced activation of key cortical systems involved in cognition and mental control," said William D.S. Killgore, principal investigator of the project.

The research was presented at SLEEP 2016, a joint meeting of the American Academy of Sleep Medicine and the Sleep Research Society.