The science behind an ADHD brain



Brain size and structure in ADHD

  • A child diagnosed with ADHD has a smaller brain than a child without the disorder.
  • A child with severe ADHD symptoms has smaller frontal lobes, and less temporal grey matter, caudate nucleus, and cerebellum. These regions of the brain  are used for concentration, to control impulses, to stay in control of inhibitions, and to produce fine motor skills. These are the four areas where a child with ADHD will have the most difficulty.
  • Diffusion Tensor Imaging (DTI) allows scientists to look more intensely at the white matter in the brains of children. White matter is made up of (axons) nerve fibres covered by myelin sheaths. DTI allows scientists to have a really good look at the nerve pathways between each different section of a child’s brain.

The cortex (otherwise known as the outer layer of the brain) is referred to as grey matter. It consists of mainly neurone cell bodies and synapses. The white matter in the brain is right underneath the grey matter. The grey matter consists of long neuronal axons covered by a fatty sheath named myelin which insulates these axons, and aids in the conduction of electrical impulses.

Diffuser Tensor imaging was used in a recent study to look at the fibre pathways in the brains of ADHD children. It was confirmed that abnormal features were found in the fibre pathways of the frontal cortex, basal ganglia, brainstem and cerebellum. These areas are involved in attention, impulsivity, inhibition and motor activity.

The study concluded that brain circuits connecting each area of the brain could be altered in a child with ADHD. This is a possible reason children with ADHD have problems with attention, behaviour and learning.

An introduction to the brain

The three major parts of the brain are the cerebellum, cerebrum, and the brainstem.

The areas of the brain which are specific to  ADHD, and to learning, concentration, behaviour and attention regulation,  include the brainstem, cerebellum, frontal lobe, parietal lobe, and the temporal lobe.

The cerebrum

The cerebrum is located in the upper skull, and is the biggest part of the brain. The cerebrum uses the information distributed to it from our five senses. Through this distribution we are able to make sense of what is exactly going on in our surroundings. The cerebrum than relays back to the person’s body how exactly they should respond.

The cerebrum is in control of our emotions, our ability to speak, have thoughts, read language and to learn. It is made up of grey matter, and is named the cerebral cortex.

Cerebal cortex:

The Cerebal cortex is divided into two left and right hemispheres. These hemispheres are connected by a thick band of nerve fibres named the corpus callosum, which allows the two hemispheres to communicate and to share information.

The two left and right hemispheres have been divided into lobes: frontal, temporal, parietal, and occipital lobes.

Frontal lobes are large complex structures, and include the motor cortex which controls movement. These lobes are required for speech, making plans, solving a problem, and for helping people to decide how to behave socially and emotionally. They also give us self – awareness and self- control.

The temporal lobes are the main areas responsible for remembering a fact or event. Together, with the support of the limbic system, they help us express, and understand emotions.

The temporal lobes effect a person’s overall personality. They are needed to hear, have an understanding of language, and to distinguish sounds made by musical instruments. The cerebellum of someone without ADHD will have more grey matter then someone with ADHD, which is why ADHD children have major problems with emotional regulation, and the processing of language.

ADHD children often have difficulty following through with instructions. Often, they are so hyperactive that they simply cannot process the language being spoken to them. It can’t be processed or understood in that moment of out of control hyperactivity.

Even if the language is processed, (which is unlikely) they will have great difficulty stopping what they doing, to put the given instructions into action. If they do put into place a plan to fulfil the task, the behaviour while doing the task will include hyperactivity, poor concentration, vocalisations and other disruptive behaviour. Anything can happen while they are trying to complete the task.

There is a lack of connection between what you are asking a child with ADHD to do, how they process what you are asking them to do, and fulfilling the task.

The parietal lobes make interpretations about sensations and messages from different parts of the brain. They make connections between the information from different senses, and store memories. These lobes interpret touch, temperature, pain, sounds, and visual information about objects and the environment. They help us understand shape, size, texture, and direction.

The occipital lobes contain the primary vision centres, as well as areas that help us visually understand, recognise objects, and help us understand what written words mean.

Underneath the surface of the cerebrum is the ‘white matter’ and deeper structures: the basal ganglia, and the limbic system, which are closely connected.

The basal ganglia are a group of structures around the thalamus, which include the putamun, globes pallibus, and caudate nucleus. The basal ganglia are important for voluntary movement, and contribute to learning skills. They control our response to reinforcement or rewards.

The limbic system is a complex network of brain areas that includes the amygdala, and the hippocampus, as well as the temporal, frontal and parietal lobes. The limbic system is the ”primitive” or ”animal” part of our brain. It controls our immediate, automatic responses to stimuli-our ”gut reactions’.

The cerebellum

The location of the cerebellum is right at the back of the brain. It keeps a person’s balance and physical, more complex movements coordinated. An action such as running or playing a violin are coordinated by the cerebellum. The cerebellum contributes to the control of speech, and participates in many of the functions  controlled by the cerebrum in ways that are not fully understood.

The brainstem

The brain and the spinal cord are connected by the brainstem. The brainstem will pass a message back and forth between parts of a person’s body and the brain. The brainstem is in control of functions like breathing, blood pressure, body temperature, heart rhythms, hunger and thirst, and sleep patterns.

What does the ADHD brain want?

ADHD brains to do not adapt to environments easily. They run on lower levels of dopamine and norepinephrine than the non-ADHD brain, which means it is challenging to keep up stimulation offered by less inspiring, or everyday tasks.

The ADHD brain is motivated by activities which enable high-stimulation, and allow for optimal arousal. This can mean elevating the existing stimulation, by wanting things louder, to go faster, to be bigger, funnier, or riskier. The more intensity, the more aroused the brain will feel.

Most people with ADHD find it difficult to modulate their own levels of stimulation, and often end up over aroused.  Laughter turns to hysteria, the engagement in fun becomes too much fun, stirring somebody up turns into a big argument, and a cuddle becomes a bear hug.

Due to poor modulation, the brain can suddenly become overloaded with stimulation. What was laughter moments ago can suddenly become tears, screaming, or an abrupt departure.

A major factor in ADHD is the brain’s  underlying challenge to self-regulate. The ADHD brain’s stimulation requirements always change in relation to internal and external demands.

The brains response to the environment is based on what is motivating the brain in that very moment, and the focus possible, given neurotransmitter levels. Whether an ADHD brain sways towards over-reactivity, or under-reactivity, these brains rarely get the balance right.



Chadian, Peter. MA, MEd &Tannock, Rosemary, PhD. 2009

Dr Ellen Littman, ‘What the ADHD brain wants, and why’


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