Sleep and Executive Function in ADHD

RESEARCH

A recent study has found that induction of slow waves during early non-rapid eye movement (non-REM) sleep may improve executive function in children with ADHD .¹ Pointing to emerging data regarding deficits in the prefrontal cortex and non-REM slow-wave sleep in the brains of children with ADHD, Munz and colleagues¹ surmised that the quality of slow oscillations during sleep may impact ADHD symptomology, particularly behavioral inhibition, an aspect of executive function.

The researchers aimed to improve daytime behavioral inhibition in children with ADHD by enhancing slow waves via bilateral slow oscillating transcranial direct current stimulation (so-tDCS; 0.75 Hz) during non-REM sleep.

They conducted a small, randomized, double-blind, crossover trial that included 14 boys, age 10 to 14 years, in whom ADHD was diagnosed. Presence of a sleep disorder or other neurological disorder was a study exclusion criterion, and all participants who were taking methylphenidate discontinued use 48 hours before experiment participation.

Participants received so-tDCS during one of the 2-night experiment. Inhibition control using a visuomotor go/no-go task, intrinsic alertness using a stimulus response task, and motor memory/visuomotor performance using a finger sequence tapping task were assessed. The go/no-go task involved display of a sad or smiling ghost on a computer screen for 200 milliseconds (40 trials). Participants were instructed to press a button only when the sad ghost appeared. The interstimulus period varied and, in 50% of the trials, a visual distractor was presented 400 milliseconds before the stimulus appeared, which the participants were to ignore.

A reaction-time task involved repeatedly being presented with the image of a witch in a centrally located window on the computer screen. Participants were instructed to press a single response button as soon as they saw the witch (30 trials). Visuomotor control was assessed by having participants view 4 boxes on the computer screen and tap, as quickly and as accurately as possible, corresponding numerals on the keyboard with their nondominant hand when a white star appeared in a box.

Four minutes after the participants entered stage 2 non-REM sleep for the first time, 5 intervals of 5 minutes of so-tDCS were applied, with a 1-minute interval between stimulations. In the sham condition, the stimulation simply remained off. The participants performed cognitive tasks immediately before going to bed for the sleep study and immediately after breakfast the following day. Bed time was 8:30 pm, wake time 6:30 am, and post-breakfast testing began at 7:30 am.

The researchers found no differences in quantitative measurements of sleep stages, total time in bed, total sleep time, or sleep efficiency between the stimulation and sham conditions. Intrinsic alertness was not affected, and motor memory performance was slightly slower in participants receiving so-tDCS. However, so-tDCS appeared to result in slowed reaction times for the go/no-go task (P = .037).

The bottom line

Lateral prefrontal slow oscillations during sleep may play a specific role in executive function in ADHD, and the induction of slow waves during non-REM sleep may potentially improve behavioral inhibition in patients with ADHD. The researchers conceded that so-tDCS itself may be unfeasible for clinical use and added that their study needs to be repeated with a non-ADHD control group.

References:

1. Munz MT, Prehn-Kristensen A, Thielking F, et al. Slow oscillating transcranial direct current stimulation during non-rapid eye movement sleep improves behavioral inhibition in attention-deficit/hyperactivity disorder. Front Cell Neurosci. 2015;9:307.