The Science of ADHD: What’s Really Happening in the Brain and Body

ADHD is more than just being distracted or full of energy.

It is about how the brain and body work together to manage focus, motivation, emotion and time. Understanding the science behind it helps explain why people with ADHD often experience the world differently, and why some of the support offered in schools and workplaces is not always effective.

What Is ADHD?

ADHD (Attention Deficit Hyperactivity Disorder) is a neurodevelopmental condition, which means the brain develops and functions in a different way. These differences affect how attention, motivation, and self-control are managed. It is not caused by poor parenting or lack of effort. It is a difference in brain wiring.

Inside The ADHD Brain

The brain is made up of networks that constantly communicate with each other. In ADHD, some of these networks work differently, especially those that manage attention, planning, reward and impulse control.

The main areas involved include:

• The prefrontal cortex: This area sits just behind the forehead and helps with planning, decision-making, organisation and self-control. In ADHD it can be less active during tasks that require focus or mental effort.

• The striatum: Found deep inside the brain, the striatum helps regulate reward and motivation. It relies on dopamine, a brain chemical that helps you feel satisfaction and drive. Studies show dopamine activity here can be lower in people with ADHD.

• The anterior cingulate cortex: This region helps you switch attention, manage emotions and notice mistakes. It can be less efficient in ADHD, which makes it harder to stay on track once attention drifts.

• The default mode network (DMN): A collection of brain regions that become active when the mind is wandering or daydreaming. In a neurotypical brain this network quietens down during focused tasks. In ADHD it often remains more active, competing with the brain’s focus system and making it harder to concentrate for long periods.

The Default Mode Network And Attention

The default mode network (DMN) is one of the most fascinating discoveries in ADHD research. It is the part of the brain that becomes active when your mind wanders, when you daydream, or when you think about yourself.

In a neurotypical brain, the DMN usually switches off when you need to focus on a task. At the same time, another system called the task-positive network switches on to help you concentrate. These two systems normally take turns: when one is active, the other quietens down.

In ADHD, this switch is less efficient. The DMN tends to stay more active even when the person is trying to focus. This means the “daydream” and “focus” networks compete for attention.

Imagine sitting down to finish a piece of work, but part of your brain keeps thinking about dinner, a conversation from last week or a song lyric stuck in your head. You are not choosing to be distracted. Your daydream network simply is not quietening as is typically expected, making focus much harder to sustain.

Many people with ADHD describe this as having too many thoughts or “too many tabs open” in their mind.

Dopamine And Motivation

At the centre of ADHD is a difference in how the brain handles dopamine, the chemical messenger that regulates reward and motivation.

When most people start a task, dopamine is released and creates a small sense of satisfaction that keeps them going. In ADHD, that dopamine signal is weaker. Tasks may not feel rewarding enough to hold attention unless they are exciting, urgent or interesting.

That is why someone with ADHD might struggle to start routine tasks but can hyperfocus for hours on something stimulating. The ADHD brain is motivated by interest and novelty rather than importance or obligation.

ADHD medication increases dopamine and noradrenaline activity in the brain. This helps balance focus and motivation so tasks feel easier to start and maintain.

What Happens In The Body

ADHD affects more than the brain. Because the brain and body are deeply connected, these differences appear physically too.

• Stress response: The body’s stress system, called the hypothalamic-pituitary-adrenal axis, can be more reactive in ADHD. This can make people feel tense, restless or easily overstimulated.

• Sleep: The body clock, known as the circadian rhythm, is often delayed in ADHD. Falling asleep or waking up at regular times can be difficult.

• Heart rate and alertness: Research shows people with ADHD may have a higher or more variable heart rate, showing that the nervous system is more sensitive to stimulation.

• Emotional regulation: Neurotransmitter differences can make emotions stronger and more changeable, which is why frustration, excitement or sadness can feel more intense.

These are not signs of weakness. They are part of how the ADHD nervous system works: quick to respond, highly sensitive, and easily overwhelmed.

What Professor James Brown says

Professor James Brown, a UK scientist and co-founder of ADHDadultUK, has helped bridge the gap between research and lived experience.

He explains that ADHD is not about knowing what to do but about doing what you already know you should. The brain can plan perfectly well but struggles to activate the plan without an immediate sense of reward or urgency.

Professor Brown also talks about time blindness, the brain’s difficulty in sensing time passing. He gives a clear example from universities, where a common “reasonable adjustment” for students with ADHD is to offer a two-week extension on assignments.

It sounds helpful, but as he points out, if a student with ADHD normally completes their work the night before it is due, giving them two extra weeks simply means they will do it two weeks later, still the night before. The difficulty is not lack of time but the way the ADHD brain experiences time and motivation.

He also highlights that many schools and workplaces are built around neurotypical patterns of focus and organisation. Without understanding how ADHD brains actually function, even well-meant adjustments can miss the mark.

What This Means Day To Day

 ADHD influences far more than concentration. It shapes motivation, sleep, emotions, memory and how time feels. People with ADHD are often creative, quick-thinking and full of ideas, but they may also struggle with organisation and follow-through.

Support works best when it matches how the ADHD brain and body function. Breaking tasks into smaller chunks, giving feedback regularly, using reminders or changing environments can help far more than simply adding extra time.

Medication, therapy and coaching can all play a role. The most effective approach starts with understanding that ADHD is a neurological difference, not a personal flaw.

Did you know?

• People with ADHD can have up to 30% lower dopamine activity in key brain regions.

• ADHD is 70–80% heritable, meaning it often runs in families.

• The default mode network in ADHD stays more active when trying to focus, which makes concentration harder.

• Around 70% of people with ADHD report sleep problems such as delayed sleep or racing thoughts at night.

The Takeaway

ADHD is biological, measurable and very real. The differences in dopamine, brain networks and time processing explain so much of what people experience day to day.

As Professor James Brown says, once you understand what is happening in the brain and body, you can stop blaming yourself and start finding what truly helps you thrive.

At SEND Meadow, we are passionate about building understanding, compassion and inclusion for children and adults with additional needs.

By sharing the science behind conditions like ADHD in plain language, we hope to help families, educators and professionals create support that truly works, support that fits the person, not the other way round.

Together, we can make awareness meaningful and ensure every neurodivergent mind is valued and understood.