Attention Deficit Hyperactivity Disorder (ADHD) is a buzz phrase that is often used to describe children (and adults) who can’t sit still. But what is ADHD really? And how do those with ADHD and those without differ in terms of behaviour and actual brain structure and function?
ADHD (formerly known as ADD) is a neurodevelopmental disorder. It affects approximately 2-5% of children and adults worldwide, with the disorder being diagnosed three times more in males than females. In 2015 over 51 million people worldwide were reported to be diagnosed with ADHD.
ADHD is characterised by an inability to pay attention, distractibility, fidgeting, excessive talkativeness and impulsivity, among other symptoms. Having some of these symptoms or characteristics does not deem somebody to have ADHD, and before looking at the differences in the brain of an ADHD and non-ADHD person it is important to note how a diagnosis is made.
Making a diagnosis
The Diagnostic and Statistical Manual V provides specific criteria that need to be met in order for a diagnosis of ADHD to be made. A diagnosis is made according to symptoms of inattention or symptoms of hyperactivity and impulsivity.
These symptoms need to be evident for at least six months and present prior to the time a child is 12 years old; they must interfere significantly in social or academic functioning, and be present in more than one setting (i.e. home and school).
In order for a diagnosis of inattentive type ADHD to be made, at least six of the following symptoms need to be present (as seen in the DSM-V):
- Often fails to give close attention to details or makes careless mistakes in schoolwork, at work, or during other activities (e.g., overlooks or misses details, work is inaccurate).
- Often has difficulty sustaining attention in tasks or play activities (e.g., has difficulty remaining focused during lectures, conversations, or lengthy reading).
- Often does not seem to listen when spoken to directly (e.g., mind seems elsewhere, even in the absence of any obvious distraction).
- Often does not follow through on instructions and fails to finish schoolwork, chores, or duties in the workplace (e.g., starts tasks but quickly loses focus and is easily sidetracked).
- Often has difficulty organising tasks and activities (e.g., difficulty managing sequential tasks; difficulty keeping materials and belongings in order; messy, disorganised work; has poor time management; fails to meet deadlines).
- Often avoids, dislikes, or is reluctant to engage in tasks that require sustained mental effort (e.g., schoolwork or homework; for older adolescents and adults, preparing reports, completing forms, reviewing lengthy papers).
- Often loses things necessary for tasks or activities (e.g., school materials, pencils, books, tools, wallets, keys, paperwork, eyeglasses, mobile telephones).
- Is often easily distracted by extraneous stimuli (for older adolescents and adults, may include unrelated thoughts).
- Is often forgetful in daily activities (e.g., doing chores, running errands; for older adolescents and adults, returning calls, paying bills, keeping appointments).
In order for a diagnosis of hyperactive/impulsive type ADHD, at least six of the following symptoms need to be present (as seen in the DSM-V):
- Often fidgets with or taps hands or feet or squirms in seat.
- Often leaves seat in situations when remaining seated is expected (e.g., leaves his or her place in the classroom, in the office or another workplace, or in other situations that require remaining in place).
- Often runs about or climbs in situations where it is inappropriate. (Note: In adolescents or adults, may be limited to feeling restless)
- Often unable to play or engage in leisure activities quietly.
- Is often “on the go,” acting as if “driven by a motor” (e.g., is unable to be or uncomfortable being still for extended time, as in restaurants, meetings; may be experienced by others as being restless or difficult to keep up with).
- Often talks excessively.
- Often blurts out an answer before a question has been completed (e.g., completes people’s sentences; cannot wait for turn in conversation).
- Often has difficulty waiting for his or her turn (e.g., while waiting in line).
- Often interrupts or intrudes on others (e.g., butts into conversations, games, or activities; may start using other people’s things without asking or receiving permission; for adolescents and adults, may intrude into or take over what others are doing).
ADHD brain development
The largest study on ADHD and the brain was conducted by Radboud University Nijmegen Medical Centre. Researchers on this study discovered that there are differences between an ADHD and non-ADHD in three broad areas – structure, function and chemistry of the brain (Understanding the ADHD Brain, 2018).
Looking at all three of these areas of difference helps us understand and acknowledge that ADHD, when properly diagnosed, is physiologically apparent and not just a result of too much sugar or poor boundaries and behaviour.
Brain structure, function and chemistry differences and in the next section the impact that these differences have on a person with ADHD will be discussed.
ADHD brain structure
Researchers discovered that an ADHD brain is structurally smaller than a person without ADHD and there is a smaller brain volume in certain areas. The differences are more notable in children than in adults, suggesting some return to normalcy into adulthood.
It has been seen that parts of the ADHD brain mature slower than they do in a non-ADHD brain (one to three years slower), and some research has shown that these parts never really catch up entirely, suggesting that while one can treat ADHD, or learn to manage it, it will always have an impact in one way or another.
In addition, the amygdala and hippocampus are smaller in those with ADHD than those without. In addition, the non-ADHD brain is generally symmetrical across the hemispheres with regard to white matter, whereas in the ADHD brain asymmetry has been observed which suggests temporal lobe function disruption.
ADHD brain function
In an ADHD brain there is decreased blood flow to the prefrontal areas implying decreased functioning in the area, which affects a variety of functions (mentioned below).
ADHD brain chemistry
Neurotransmitters are chemicals in the brain that send messages across various synapses (small gaps), from one neuron (nerve cell) to another target neuron, muscle cell or gland cell. These target neurons are receptors and need to be able to pick up the message that is sent.
These messages are sent from the brain and help the body know what to do or how to react to a certain stimulus or situation. The brain also has transporters called re-uptake inhibitors, which avoid too much of a certain chemical being absorbed.
Dopamine is one of the main neurotransmitters and is considered to have an important effect on mood, attention and motivation. In order for the dopamine to work effectively in our body, the message has to be passed along the synapses effectively.
It has been discovered over time that there is a dysregulation of dopamine in an ADHD brain. It seems that it either has too little dopamine or has too many re-uptake inhibitors and therefore the dopamine is removed too quickly and it does not have enough time to exert its effect on the brain and the rest of the body.
Medications like Ritalin or Concerta blocks these re-uptakers and therefore slows down the removal of dopamine, allowing it to have its desired effect.
Many children are medicated in order to maintain focus, concentration and ‘good behaviour’ when they may not actually have ADHD. Taking Ritalin or Concerta when you don’t not have ADHD (as described above in terms of structure and chemistry of the brain) will likely still help improve concentration, but will likely not be effective in the long term, as the underlying causes for concentration deficits or hyperactivity could be related to other difficulties or disorders.
How does ADHD affect the brain?
Based on the aforementioned differences, the effects of ADHD can be seen across a range of areas and while a child or person is engaging in a variety of different tasks or challenges.
- The amygdala and hippocampus are the areas responsible for emotional maturity and impulsivity, which explains why those with ADHD struggle with social relationships (in the earlier years) and may be impulsive and careless in the undertakings of their tasks. Asymmetry of the two brain hemispheres will result in less communication between the two sides and more difficulties controlling impulses, and maintaining a balance between rationality and emotionality.
- The prefrontal cortex and prefrontal areas are responsible for executive functioning such as planning, organising, paying attention, remembering and our emotional responses. As a result, a person with ADHD will struggle to plan their work and keep organised. They may be forgetful, struggle to pay attention to instructions or information that is presented to them and become easily distracted.
Those with ADHD may find it difficult to start or complete tasks timeously. Because there are increased demands in the realm of executive functioning that are placed on a person as they grow older, difficulties in these areas are often only noticed later into childhood or adolescence. Children with ADHD will struggle to keep focused and motivated for longer periods and seek instant gratification and reward.
Dopamine is a main factor contributing to the presence of ADHD. Lower levels of dopamine will affect motivation and therefore mood and attention. ADHD symptoms may also be present due to lower levels of serotonin and norepinephrine in the brain.
Serotonin influences mood, memory, social interactions and behaviour. Norepinephrine can function as a stress hormone, and when it does, it affects attention and ability to focus.
There are notable differences on brain scans, such as an MRI or PET scan, of those with ADHD and those without. It can be noted from the ADHD brain scans that there is considerably less activity taking place in an ADHD brain than a non-ADHD brain, especially in the frontal lobe areas.
Brain scans are not used to diagnose ADHD as there can be a variety of factors responsible for more or less activity. In addition, brain scans are only indicative of activity at the time the scan was done and cannot necessarily generalise about symptoms going forward.
However, it is interesting to see how certain areas light up in a non-ADHD brain where they don’t in an ADHD brain, which is likely happening in a classroom or work environment where a child’s brain does not ‘activate’ in order for them to execute and complete tasks effectively.
Some interesting correlations
Some links have been found between a low APGAR score and ADHD. The APGAR score measures a variety of physical signs when a baby is born, such as Activity (muscle tone), Pulse, Grimace (reflex ability), Appearance (skin colour) and Respiration. Points are awarded as either 0, 1 or 2 for each indicator.
Premature birth has also been linked to ADHD. There have also been some associations found between childhood asthma and adolescent ADHD. Difficult pregnancies, alcohol use or smoking during pregnancy and exposure to lead, pesticides or other chemicals have also been found to have an effect.
While there are no clear connections between the above factors and ADHD at this stage, all of the aforementioned factors could hint at sub-optimal foetal health and development which will, therefore, be a cause or preceding factor of ADHD.