LEC 11: ADHD

What is ADHD?

• a developmental disorder

• persistent pattern of inattention and/or hyperactivity-impulsivity

• must be shown to impact development significantly

Symptoms for each type of ADHD

Inattentive type:

• often distracted

• has problems staying focused

• often loses things

Hyperactive/impulsive type:

• excessive fidgeting

• not able to stay seated

• interrupts or intrudes on others

Common neuropsychological tests (behavioural markers) used to explore symptoms of frontal lobe dysfunction

• rewards have less of an influence over the behaviour of children with ADHD

• common tests include:

  • the Stanford marshmallow experiment

  • Go, No-Go Task

  • Iowa Gambling Task

Dual pathway model

A theory about ADHD suggesting dysfunctions in executive function and reward systems contribute to the disorder.

Etiology of ADHD

ADHD is up to 80% genetic

Risk factors to developing ADHD

• perinatal hypoxia: a temporary shortage of oxygen around the time of birth

• children with a specific mutation in the dopamine reuptake transporter (DAT1) are more likely to exhibit symptoms of ADHD if their mothers smoked during pregnancy

Popular drugs used to treat ADHD

methylphenidate (Ritalin/Concerta), amphetamine (Adderall), and d-amphetamine (Dexedrine)

Mechanism of action of common drugs used to treat ADHD

• ADHD medications target the dopamine system in the brain

• the dopamine transporter normally moves unbound dopamine from the synapse into the sending neuron

• methylphenidate (Ritalin) and cocaine both block the dopamine transporter, causing dopamine to build up in the synapse

Prevalence of ADHD

• prevalence of ADHD is about 7.6%

• male to female ratio is about 3:1

Alerting network

• includes the frontal cortex, parietal cortex and the thalamus that interact to support attention

• this network is weaker in individuals with ADHD

Frontostriatal circuit

• the ventral anterior cingulate cortex and the dorsal anterior cingulate cortex control affective and cognitive components of executive control

• also includes the putamen, nucleus accumbens and caudate nucleus

• in ADHD there are abnormalities in this circuit which extend to the amygdala and cerebellum