Reviewed by Kate Anderton, B.Sc. (Editor) Jan 17 2020
Attention-deficit hyperactivity disorder (ADHD) is a neurobiological disorder characterized by symptoms of hyperactivity, inattention and impulsivity. People with the condition are often prescribed a stimulant drug called methylphenidate, which treats these symptoms. However, scientists do not fully understand how the drug works.
Now, researchers at the Okinawa Institute of Science and Technology Graduate University (OIST) have identified how certain areas of the human brain respond to methylphenidate. The work may help researchers understand the precise mechanism of the drug and ultimately develop more targeted medicines for the condition.
Previous research suggests that people with ADHD have different brain responses when anticipating and receiving rewards, compared to individuals without ADHD. Scientists at OIST have proposed that in those with ADHD, neurons in the brain release less dopamine - a 'feel-good' neurotransmitter involved in reward-motivated behavior - when a reward is expected, with dopamine neurons firing more when a reward is given.
In practice, what this means is that children, or even young adults, with ADHD may have difficulty engaging in behavior that doesn't result in an immediate positive outcome. For example, children may struggle to focus on schoolwork, as it may not be rewarding at the time, even though it could ultimately lead to better grades. Instead, they get distracted by external stimuli that are novel and interesting, such as a classmate talking or traffic noises." Dr Emi Furukawa, first author of the study and a researcher in the OIST Human Developmental Neurobiology Unit, led by Professor Gail Tripp
Scientists believe that methylphenidate helps people with ADHD maintain focus by influencing dopamine availability in the brain. Therefore, Dr Furukawa and her colleagues set out to examine how the drug affects a brain region called the ventral striatum, which is a vital component of the reward system and where dopamine is predominantly released.
"We wanted to take a look at how methylphenidate affects the ventral striatum's responses to reward cues and delivery," said Furukawa.
The study, which was recently published in the journal Neuropharmacology , was jointly conducted with scientists at D'Or Institute for Research and Education (IDOR) in Rio de Janeiro, Brazil. The collaboration allowed the researchers to combine expertise across multiple disciplines and provided access to IDOR's functional magnetic resonance imaging (fMRI) facility. Delving into the brain
The researchers used fMRI to measure brain activity in young adults with and without ADHD as they played a computer game that simulated a slot machine. The researchers scanned individuals in the ADHD group on two separate occasions – once when they took methylphenidate and another time when they took a placebo pill. Each time the reels of the slot machine spun, the computer also showed one of two cues, either the Japanese character み (mi) or そ (so). While familiarizing themselves with the game before being scanned, the participants quickly learned that when the slot machine showed み, they often won money, but when the slot machine showed そ, they didn’t. The symbol み therefore acted as a reward-predicting cue, whereas そ acted as a non-reward-predicting cue. Related Stories
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