[P1.04]: The protein kinase Dyrk1A regulates cell number during the development of the central nervous system

This review provides an overview of the main imaging studies that investigated the neurobiological substrate of attention deficit hyperactivity disorder (ADHD) a common and impairing neuropsychiatric disorder with preschool onset. Three subtypes have been proposed: inattentive, hyperactive-impulsive and combined type. Researchers have emphasized poor behavioural inhibition as the central impairment of the disorder. Impairment of the ‘‘hot’’ affective aspects of executive functions like behavioural inhibition and attention and the more cognitive, ‘‘cool’’ aspects of executive functions like self-regulation,workingmemory, planning, cognitive flexibility are often reported by studies on ADHD. The hot executive functions are associated with ventral and medial regions of prefrontal cortex (anterior cingulated cortex) and named hotbrain and the cool executive functions are associated with dorsolateral prefrontal cortex and are called coolbrain. Methods: The paradigms mostly used in functional magnetic resonance imaging (fMRI) are tasks of motor inhibition, interference and attention like the go/no-go, stop-signal and the Stroop. Results from previous studies: Convergent data from neuroimaging, neuropsychological, genetics and neurochemical studies consistently point to the involvement of fronto-striatal circuitry asa likely contributor to thepathophysiologyofADHD.This circuitry involves the lateral prefrontal cortex, the dorsal anterior cingulate cortex, the caudate nucleus and putamen. A growing literature demonstrates abnormalities affecting other cortical regions and the cerebellum. Anatomical studies suggest widespread reductions in volume throughout the cerebrum and cerebellum. Functional imaging studies suggest that affected individuals activate more diffuse areas than controls during the performance of cognitive tasks. Reduction in volume has been observed in the total cerebral volume, theprefrontal cortex, thebasal ganglia (striatum), thedorsal anterior cingulate cortex, the corpus callosum and the cerebellum. Hypoactivation of the dorsal anterior cingulate cortex, the frontal cortex and the basal ganglia (striatum) have also been reported. Discussion: Some guidelines for future functional magnetic imaging studies are suggested.