Thirty minutes of aerobic exercise can give people with ADHD a short-term boost in cognition, according to a new study from researchers in Taiwan.
The team, led by neuroscientist Hsiao-I Kuo from National Taiwan University, also found exercise that gets your heart pumping such as fast walking, jogging, swimming, dancing, or cycling ramped up inhibition in the motor cortex for people with attention-deficit hyperactivity disorder (ADHD), while those without the disorder saw quite the opposite result.
We already know that in healthy people who aren't diagnosed with ADHD, aerobic exercise tends to enhance excitability in the brain's 'higher thinking' layer, or cortex, and reduces processes that otherwise inhibit its neural activity.
A similar effect is seen when non-ADHD people take methylphenidate, a common drug treatment for ADHD that increases levels of the neurotransmitters dopamine and norepinephrine.
When people with ADHD take the stimulant methylphenidate (sold under brand names like Ritalin), on the other hand, intracortical inhibition increases. This might explain some of its 'focusing' effects: other studies have found that in general, people with ADHD have significantly lower levels of intracortical inhibition than the general population.
This prompted the team to question: would aerobic exercise affect people with ADHD differently? If it 'normalizes' their intracortical inhibition, as methylphenidate does, could it improve their cognitive performance, too?
Twenty-six unmedicated people with ADHD participated in the study, all around the age of 23 and otherwise healthy, along with 26 non-ADHD counterparts.
In two separate exercise sessions, each person spent 30 minutes on a stationary exercise bike, starting with a 5-minute warm-up, then a 20-minute workout, and a 5-minute cool-down.
Two other sessions were designed as 'controls': participants sat on the exercise bike for 30 minutes watching a nature documentary series.
Before and after one of these exercise or control sessions, Kuo's team tested everyone's performance on a few cognitive tasks: one that assesses the person's ability to 'pull back' from an activity on command, as a measure of inhibitory control, and another that tests motor learning, which is essentially 'muscle memory'.
Before and after the remaining exercise and control sessions, they used TMS (transcranial magnetic stimulation) to measure short-interval intracortical inhibition (SICI) and facilitation (ICF).
TMS allows the scientists to test the strength of signals between the motor cortex and muscles around the body, which to some extent indicates the excitability of neurons and the modulation of channels that keep the whole network in check.
Aerobic exercise increased SICI in ADHD participants, who also performed better in both inhibitory control and motor learning tasks post-workout.
The non-ADHD participants also saw improvement in motor learning after exercise, though it actually decreased their SICI, and had no clear effect on their inhibitory control.
"A single bout of aerobic exercise transiently increases cortical inhibition in adults with ADHD, which is determined primarily by the GABAergic system," Kuo and team write. "This might lead to improvements in inhibitory control and motor learning in ADHD patients."
The study doesn't tell us whether these distinct results are linked in any causal way, but they certainly point to future avenues for research.
Kuo and team say 30-minute bouts of aerobic exercise could benefit some patients with ADHD with respect to cognitive performance in the short-term. However, there's no evidence that it would work as a standalone strategy, and it's unclear how long the effects last.
The research was published in Psychiatry Research.