OADES, R. D. & MÜLLER, B. (1997).
The development of conditioned blocking and monoamine metabolism in
children with attention-deficit-hyperactivity disorder or complex
tics and healthy controls: an exploratory analysis. Behavioural
Brain Research, 88, 95-102. (request
a copy)
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Introduction:
Conditioned blocking (CB) measures the transient suppression of learning
that a new stimulus, added during learning, has the same consequences
as the conditioned stimulus already present. Normal CB increases from
puberty across adolescence, between the age of 8 and 20 years (Oades
et al., 1996). Is there a delay in the development of selective attention
abilities in children with a primary diagnosis of attention-deficit/hyperactivity
disorder (ADHD) and does this differ from children with Tourette syndrome
who also express some symptoms of attention deficit?
Methods:
CB development was compared between 13 healthy children (CN: mean age
11.0 years), 13 with attention-deficit/hyperactivity disorder (ADHD:
mean 10.5y) and 11 with complex tic or Tourette syndrome who also showed
some attention-deficit symptoms (TS: mean 11.8y). The ADHD group were
medication naive, but 3 TS were receiving tiapride, and two pimozide.
The 'mouse-in-house' task form was used.
Results:
1. All children required fewer trials to learn the task with increasing
age: (the ADHD group was slightly slower).
2. However, only healthy controls improved CB with increasing
age (figure 1, left).
3. TS patients under 11y tended to show impaired CB, and over 11y they
were significantly worse than controls.
4. While ADHD children over 11y showed less CB than controls, under
11y they tended to show more CB.
5. A correlational analysis of the status of monoamine metabolism in
24h urine samples showed a positive relationship for CB with dopamine
(DA) metabolism in normal and TS children, but a negative relationship
in ADHD patients (figure 1, right).
6. In contrast, increases of serotonin (5-HT) metabolism were negatively
related to CB in TS, but positively related to CB in ADHD children (figure
1, right).
7. Both ADHD and TS groups showed a depressed NA turnover
compared to normal children: but the ADHD showed a marked suppression
of the ratio of DA and 5HT metabolites (i.e. HVA/5HIAA) that reflected
their higher 5-HIAA levels. [The TS group showed increased DA turnover
possibly reflecting medication.] see figure 2.
Conclusions:
When selective information processing abilities reflected by CB start
to develop at the onset of puberty, there is a relative worsening in
ADHD patients. In contrast TS patients show an impairment independent
of age. Changes in the balance between dopamine and serotonin systems
may contribute to normal and to abnormal cognitive development.
We reported on the development of CB in normal
children and adolescents in 1996
.
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