THE DEVELOPMENT OF CONDITIONED BLOCKING AND MONOAMINE METABOLISM IN CHILDREN WITH ATTENTION-DEFICIT-HYPERACTIVITY DISORDER OR COMPLEX TICS AND HEALTHY CONTROLS - AN EXPLORATORY ANALYSIS

Conditioned blocking (CB) measures the transient suppression of learni ng that a new stimulus, added during learning, has the same consequenc es as the conditioned stimulus already present. Normal CB increases be tween the age of 8 and 20 years (Oades, R.D., Roepcke, B. and Schepker , R., A test of conditioned blocking and its development in childhood and adolescence: relationship to personality and monoamine metabolism, Dev. Neuropsychol., 12 (1996) 207-230). In the present study CB devel opment is compared between healthy children (CN), children with attent ion deficit (ADHD) and those with complex ties or Tourette's syndrome (TS) with mean ages of 10-11 years. All children needed fewer learning trials with increasing age: the ADHD group showed a slight impairment . Only controls improved CB with increasing age. A trend for worse CB in the TS than the other groups was significant for those over 11 year s. While ADHD children over 11 years showed less CB than controls, you nger ADHD children showed more. A correlational analysis of the status of monoamine metabolism in 24 h urine samples showed a positive relat ionship for CB with dopamine metabolism in controls and TS children, b ut a negative relationship in ADHD children. In contrast, increases of serotonin metabolism were negatively related to CB in TS but positive ly in ADHD patients. In conclusion, when selective information process ing abilities reflected by CB start to develop at puberty-onset, there is a relative worsening in ADHD patients. But TS patients show an imp airment independent of age. Changes in the balance between dopamine an d serotonin systems may contribute to normal and abnormal cognitive de velopment. (C) 1997 Elsevier Science B.V.