Functional magnetic resonance imaging (MRI), during performance of two tasks requiring high-level executive control, was studied in seven adolescent boys with ADHD, and compared to nine controls, at the Institute of Psychiatry, Kings’ College, London, UK. A “stop“ task required inhibition of a planned motor response, and a “delay“ motor timing task required the synchronization of a motor response to an intermittently appearing visual stimulus. Adolescents with ADHD showed less brain activity, predominantly in the right hemisphere mesial frontal cortex during both tasks, and in the right inferior prefrontal cortex and left caudate nucleus during the stop task. ADHD is associated with subnormal activation of the prefrontal areas responsible for higher-order, inhibitory motor control. 
COMMENT. Motor attention and response selection, impaired in patients with ADHD, is associated with hypofunction of the right mesial frontal lobe and striatal areas. The findings in these functional MRI studies corroborate previous documentation by quantitative MRI of structural changes in the frontal lobe and caudate in ADHD children. (see Progress in Pediatric Neurology III. PNB Publ, 1997;p212; and Vol. II. 1994;ppl72-184).
The role of the right frontal lobe in humor appreciation is evaluated at the University of Toronto and Rotman Research Institute, Baycrest Centre for Geriatric Care, Canada . In patients with damage to the right frontal lobe, the physical or emotional responses of laughter and smiling were diminished, and impaired performance on humor appreciation tests was correlated with cognitive deficits. Working memory, or the ability to retain information, was related to appreciation of verbal (jokes) and non-verbal (cartoon) tests.
A right frontal lobe dysfunction may explain the anhedonia characteristic of some children with ADHD.