Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
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The neuroactivation pattern observed in the hyperactive adolescents differed quantitatively and qualitatively from that of comparison subjects during performance of two tasks testing high-level motor control. The hyperactive adolescents showed reduced brain activation in right-hemispheric mesial frontal cortex during both tasks, and right inferior prefrontal cortex and left caudate nucleus during the stop task. The reduced activation in anterior cingulate in both paradigms further supports its attributed role in output related attention, and leads to the suggestion that motor attention is the underlying cause of the executive deficits in ADHD. The reduced right hemispheric inferior frontal and caudate activation in the adolescents with ADHD during the stop task seems to reflect a weakness in a specific network for motor response inhibition.

The finding reported here of hypofrontality in the hyperactive adolescents, is in line with the hypothesis of a maturational lag as the cause of ADHD, emphasizing the late development of the frontal lobes. This is further supported by our results of reduced power of response in frontal lobe structures in healthy adolescents compared to adults. It thus appears that frontal lobe activation during performance of executive paradigms becomes more pronounced with age and is reduced by pathology. Adolescent hypofrontality was in premotor cortex in the stop task and in mesial and inferior frontal lobe in the delay task. The fact that the increase in frontal signal response was more pronounced in the motor timing task, in which adults performed better than adolescents, suggests that there is an interrelationship between frontal activation, age and performance. It seems that those functions that continue to develop into adulthood, are subserved by age-increasing blood flow dynamics in the responsible brain regions. A more "immature" performance pattern in the adolescents with ADHD is likely -decreased performance may not have reached significance due to small statistical power; if so, it would parallel a reduced BOLD signal in the responsible frontal brain regions.

In summary, it has been shown that fMRI is a feasible technique to investigate the underlying neural mechanisms of cognitive functioning in a difficult developmental disorder such as ADHD. Our findings of hypofrontality in adolescents with ADHD and of healthy adolescents compared to adults on the same executive paradigms seems to support the hypothesis of a maturational lag in ADHD pathology.

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