What is “attention”?

Attention is a consistent mental effort. It is our ability to complete our trains of thoughts as intended, to be salient when we process the information, and to execute what we decide to do.

What happens in our brain?

In our brain there are many messages going around all the time. Most of them are irrelevant. When we want to execute a task, our brain sends a group of electrical impulses to the rest of the brain for coordination by inhibiting irrelevant messages in order to keep us focused.

Each electrical impulse is passed from one nerve cell to another chemically through a space (synapse), via ‘neurotransmitters’.

Dopamine is one of the chemical neurotransmitters. Sometimes, the brain may produce too much dopamine into a synapse. Evolutionarily, we have ‘dopamine transporters’ to re-uptake excessive dopamine back to the previous nerve cell.

What happens in the brain of people with ADHD?

An important cause of ADHD is the over production of dopamine transporters which is due to genetic makeup.

Excessive dopamine transporters lead to inadequate dopamine in the synapse. Therefore the inhibitory impulse cannot be passed on to the next nerve cell. As a result, the person is overwhelmed by irrelevant thoughts or behaviors. Clinically ADHD people are easily distracted, hyperactive and impulsive.

How does the medication work?

The stimulant medication, methylphenidate, works by temporarily blocking the excessive dopamine transporters, to allow appropriate amount of dopamine required for inhibition.

It takes about 15 to 30 minutes for the medication to start working, and in about 3 to 5 hours, it leaves the body in the urine. It is like wearing our glasses: when we put them on, we can focus. When we take them off, they are off.

Norepinephrine is another neurotransmitter also involved in ADHD. Atomoxetine is a medication which works mainly on norepinephrine.

There are other ADHD medications, mainly amphetamine derivatives are not approved in many places, including Hong Kong.