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Understanding the neuroscience of an ADHD brain

Researcher & Writer: Lianna LEE

Illustrator: Ellie LIU

Attention Deficit Hyperactivity Disorder (ADHD) is one of the most common neurodevelopmental disorders that is distinguished by persistent patterns of inattention, hyperactivity, and impulsivity. Usually, ADHD is first diagnosed during one’s childhood, and can often last into their adulthood. ADHD can also be diagnosed in adults.

ADHD can be diagnosed as one of the three different types:

  1. Predominantly Inattentive Presentation

  2. Predominantly Hyperactive-Impulsive Presentation

  3. Combined Presentation

6 symptoms of ADHD within each type must occur frequently for children or adolescents under 17 years of age to be diagnosed with ADHD, and 5 symptoms must be shown for people over 17. Here are some symptoms for the following types:

1. Predominantly Inattentive

→ Hard for the individual to pay close attention to details

→ Difficulty in staying focused on tasks or activities, such as during conversations

→ Often loses things needed for daily activities

→ Easily Distracted

→ Problems in organizing tasks and work; poor time management

2. Predominantly Hyperactive-Impulsive

→ Has difficulty with waiting for their turn

→ Blurts out an answer before a question has been finished

→ Intense Fidgeting

→ Interrupts others

→ Hard for the individual to listen to instructions

3. Combined

→ Symptoms of the above 2 types of ADHD are equally present in the individual.

The specific cause of ADHD is unknown, however there is evidence that genes play a huge factor in contributing to ADHD. Other factors that may be the cause of the development of ADHD include premature delivery, alcohol and tobacco usage during pregnancy, brain injury, and more.

Researchers have studied many structural and functional brain differences between those with ADHD and others without the disorder, such as brain size, neurotransmitters, etc. It has been found that people with ADHD may have areas of the brain that develop at a slower rate with different activity levels.

The pre-frontal cortex is in charge of controlling emotions, impulsivity, and aggression. Those diagnosed with ADHD have a pre-frontal cortex that is weaker in function and is thinner, which could explain why they present behaviours that may be disruptive and impulsive. The pre-frontal cortex is located in the frontal lobe, which is the area at the front of the brain responsible for decision-making and problem-solving skills, and even plays a role in concentration and attention. This could be the reason why individuals with ADHD lack time management skills and are unable to make decisions.

The limbic system regulates our emotions, like impulse control or restlessness. In a 2017 study that looked at ADHD, it was discovered that people with ADHD have dysfunction in this area of the brain, accounting for the difficulty in controlling emotions.

The amygdala, a part of the limbic system, was also found to be smaller in individuals with ADHD. This part of the brain is linked with experiencing emotions, especially fear and aggression. Emotional dysregulation is another deficit in functioning related to ADHD that is characterised by quick changes in mood. This could be the result of variations in the amygdala.

Moreover, in a 2017 study, the cerebellum was found to be smaller in volume in the brains of children with ADHD. As the cerebellum is associated with motor movements such as balancing control and coordination, this may explain the motor delays often seen in children with ADHD.

The neural pathways in an ADHD brain also do not connect and mature at the same rate, which leads to the difficulty in concentrating and paying attention. Additionally, decreased blood flow to brain regions and different neurotransmitter activity as well as functioning have been demonstrated in the ADHD brain. There are many other parts of the ADHD brain that differ in structure, and as a result of this has led to dysfunction in some areas.

There are key signs that can allow one to identify the presence of ADHD in children, this may include the inability to focus on one activity and complete it due to boredom, or even excessive energy which leads to talking and making noise excessively. Furthermore, signs of ADHD in adults could include finding it hard to listen to others during a conversation due to a lack of focus, time management concerns like procrastination, or having a negative self-image of themselves.

*Please remember to always consult a professional like a psychiatrist and seek help if there are any concerns regarding the diagnosis of ADHD.


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