Atypical motor and sensory cortex activation in attention-deficit/hyperactivity disorder: a functional magnetic resonance imaging study of simple sequential finger tapping.

BACKGROUND: Attention-deficit/hyperactivity disorder (ADHD) has been shown to be associated with anomalous motor development, including excessive overflow movements. The neurological basis of these deficits has not been established. Functional magnetic resonance imaging (fMRI) was used to determine whether differences in brain activation during sequential finger tapping are present in children with ADHD compared with typically developing control subjects. METHODS: Twenty-two right-handed children between 8 and 12 years old, 11 with ADHD and 11 typically developing control subjects closely matched for age and gender, performed self-paced sequential finger tapping during fMRI acquisition. RESULTS: There were no significant between-group differences in speed of sequential finger tapping. The between-group whole-brain comparison showed greater magnitude of activation for control subjects than children with ADHD in the right superior parietal lobe during both right-handed and left-handed finger tapping. The region-of-interest analysis within Brodmann Area 4 revealed that children with ADHD showed a significantly smaller extent of fMRI activation in the primary motor cortex contralateral to the finger-sequencing hand. CONCLUSIONS: Despite similar speed of sequential finger tapping, children with ADHD showed decreased contralateral motor cortex and right parietal cortex activation during both right-handed finger sequencing (RHFS) and left-handed finger sequencing (LHFS). The fMRI findings suggest that children with ADHD have anomalous development of cortical systems necessary for execution of patterned movements.

fMRI evidence that the neural basis of response inhibition is task-dependent.

Event-related fMRI was used to investigate the hypothesis that neural activity involved in response inhibition depends upon the nature of the response being inhibited. Two different Go/No-go tasks were compared-one with a high working memory load and one with low. The 'simple' Go/No-go task with low working memory load required subjects to push a button in response to green spaceships but not red spaceships. A 'counting' Go/No-go task (high working memory load) required subjects to respond to green spaceships as well as to those red spaceships preceded by an even number of green spaceships. In both tasks, stimuli were presented every 1.5 s with a 5:1 ratio of green-to-red spaceships. fMRI group data for each task were analyzed using random effects models to determine signal change patterns associated with Go events and No-go events (corrected P< or =0.05). For both tasks, Go responses were associated with signal change in the left primary sensorimotor cortex, supplementary motor area (SMA) proper, and anterior cerebellum (right>left). For the simple task, No-go events were associated with activation in the pre-SMA; the working memory-loaded 'counting' task elicited additional No-go activation in the right dorsolateral prefrontal cortex. The findings suggest that neural contributions to response inhibition may be task dependent; the pre-SMA appears necessary for inhibition of unwanted movements, while the dorsolateral prefrontal cortex is recruited for tasks involving increased working memory load.