The impact of methylphenidate reward sensitivity and learning processesin children with ADHD.

The department of Clinical Neuropsychology of the VU University in Amsterdam
holds an international research program into disruptive problem behaviour, with
the main focus on ADHD (prof. dr. Oosterlaan, prof. dr. Sergeant, dr. M.
Luman). The research group studies neurocognitive dysfunctions by the use of
highly sensitive computer tasks and brain imaging techniques. One of the recent
findings is that children with ADHD are more dependent on rewards to perform
optimally. An underlying shortage of dopamine (DA) in the fronto-striatal
system has been offered as a potential explanation.

Activity in the striatum is highly important for learning processes in the
presence of reward cues. Receiving a reward results in an increase in DA in the
fronto-striatal system, which enhances stimulus-response (S-R) learning in the
face of reward cues?

Findings in recent studies by dr. Luman are in line with fronto-striatal
abnormalities in ADHD: (1) children with ADHD need more reward and penalties
than controls in order to perform optimally, and (2) children with ADHD show
impaired S-R learning.

Strikingly, not much is known about the impact of methylphenidate (MPH, the
most prescribed drugs to treat ADHD) on the sensitivity to reinforcement such
as reward. MF blocks the reuptake of AD and possibly MPH can normalize activity
in the fronto-striatal system. This would result in an increase in DA
reactivity in response to reward and possible enhanced S-R learning. This has
never been investigated and therefore the impact of MPH on reward sensitivity
and S-R learning will be studied.

During the tasks, the heartrate of children will be measured by three
electrodes attached to the ribs. Heartrate measures are sensitive to receiving
rewards. A larger sensitivity to reward when children with ADHD are taking MF
would be visible in an increased heartrate response to reward.

Hypothesis
- Can MPH normalize S-R learning and is this effect mediated by an enhanced
sensitivity to contingencies.

Mapping the impact of MPH on reward sensitivity and learningprocesses in
children with ADHD (attention deficit hyperactivity disorder).

In 33 children with a DSM-IV diagnosis of ADHD (age 8 to 12), the impact of MPH
on reward sensitivity and learning processes will be investigated. This study
will be embedded in the outpatient clinic for children with ADHD at the
Bascule, academic centre for child and adolescent psychiatry in Duivendrecht
during the medication trial (four weeks), a standardised procedure to set
children to the correct doses of MPH. To investigate the impact of MPH on
reward sensitivity and learning, during each week of the trial the child will
be asked to perform three computerized tasks, which score is compared to a
baseline score preceding the trial. The baseline score of the ADHD group will
be compared to the score of a group of 33 healthy control children (1
measurement without medication, age 8 to 12) to determine whether children with
ADHD show an abnormal reinforcement sensitivity and abnormal S-R learning,
which may (or may not) be normalized by the effect of MPH.

There are no risks associated with this study.