Unlocking ADHD writer Tan Si Jie explores the science behind the development and the process of ADHD.
Mental conditions often present with few physical symptoms, making it difficult for people who are not exposed to it to understand what is happening, and why it happens. Today, we aim to explore what exactly happens in the brains of people with ADHD, and why they experience things the way they do.
Some neuropsychological studies have shown that the frontal cortex and basal ganglia play a major role in executive functioning, which is significant in directing attention and practising inhibition. Brain imaging in individuals with ADHD have shown lower activity in the right inferior prefrontal cortex and the left caudate during activities that require the coordination of physical reflexes to sensory cues.
Dopamine Deficiency
People with ADHD are often found to have deficits in the reward centres of the brain, particularly the dopamine system, where children may have low dopaminergic characteristics. ADHD stems from insufficiency of a particular neurotransmitter: norepinephrine (a.k.a. noradrenaline). Each molecule of norepinephrine is composed of dopa. Dopa molecules are converted into dopamine, which is then converted into norepinephrine. ]
ADHD typically involves a deficit of norepinephrine activity in four specific sections of the brain:
- Frontal cortex: manages and controls high-level functioning such as directing and organising attention, as well as executive function and more
- Limbic system: coordinates emotional and behavioural responses
- Basal ganglia: directs communication within the brain, similar to the control tower of an airport. It is heavily involved in motor coordination as well as habit formation, rewards and reinforcement
- Reticular activating system (RAS): a network of neurons that aid the hypothalamus in regulating behaviour
The main neurotransmitters associated with the frontal lobe are catecholamines, which influence dopaminergic and noradrenergic neurotransmission. Studies have shown these to be the main targets of ADHD medication. Norepinephrine deficiencies in these four areas contribute to the symptoms of ADHD. People with ADHD often experience sensory overload, and have increased awareness of stimuli. They are unable to distinguish between what requires focus and what is simply noise, and hence have difficulties focusing.
It has been found that complications such as low birth weight during pregnancy and childbirth may contribute to the development of ADHD in children, through the impairment of certain aspects of neuropsychological functioning. However, these factors are insufficient to explain the development of ADHD, and these effects can often be reduced through parenting methods and provision of a nurturing environment. On the other hand, environmental factors during the gestational period, such as maternal smoking, or food additivessij, may influence the severity of symptoms of ADHD.
While some people believe that the consumption of excessive amounts of sugar can contribute to hyperactive behaviour, there is no evidence that the consumption of refined sugar is a cause of ADHD.
To summarise, ADHD is caused by insufficient norepinephrine and deficiencies in the dopamine system in four main sections of the brain: the frontal cortex, the limbic system, the basal ganglia and the reticular activating system.
