Improving executive function using transcranial infrared laser stimulation

Abstract

Transcranial infrared laser stimulation is a new non-invasive form of low-level light therapy that may have a wide range of neuropsychological applications. It entails using low-power and high-energy-density infrared light from lasers to increase metabolic energy. Preclinical work showed that this intervention can increase cortical metabolic energy, thereby improving frontal cortex-based memory function in rats. Barrett and Gonzalez-Lima (2013, Neuroscience, 230, 13) discovered that transcranial laser stimulation can enhance sustained attention and short-term memory in humans. We extend this line of work to executive function. Specifically, we ask whether transcranial laser stimulation enhances performance in the Wisconsin Card Sorting Task that is considered the gold standard of executive function and is compromised in normal ageing and a number of neuropsychological disorders. We used a laser of a specific wavelength (1,064 nm) that photostimulates cytochrome oxidase - the enzyme catalysing oxygen consumption for metabolic energy production. Increased cytochrome oxidase activity is considered the primary mechanism of action of this intervention. Participants who received laser treatment made fewer errors and showed improved set-shifting ability relative to placebo controls. These results suggest that transcranial laser stimulation improves executive function and may have exciting potential for treating or preventing deficits resulting from neuropsychological disorders or normal ageing.

Keywords: Wisconsin Card Sorting Task; executive function; low-level light therapy; neuroenhancement; prefrontal cortex; transcranial infrared laser stimulation.

© 2015 The British Psychological Society.

Figures

Figure 1. Locations targeted by LLLT administration

LLLT was applied to both locations for 4 one-minute treatments each, beginning with the location 1 (the lower location) and alternating between the two locations, for a total of 8 one-minute treatments.

Figure 2. Participant interface for the Wisconsin Card Sorting Task

The top row contains the four reference cards that are displayed on every trial, and the bottom row shows the target card for an example trial. The subject sorts each target card into one of the four groups represented by the reference cards. Cards vary on color (red, green, blue, or yellow), shape (circle, star, square, or cross), and number (1, 2, 3, or 4).

Figure 3. Results

A) Overall accuracy across all trials for the two groups. The active laser treatment group correctly sorted the cards more often than the placebo group. B) Trials to criterion for each of the first four rules learned. The placebo treatment group took significantly longer to reach criterion on the second rule than the active laser treatment group, suggesting a benefit in set shifting ability in the active treatment group. Error bars represent standard errors.