I know of no specific rule, but you could certainly wing one.
ADHD
A character suffering from ADHD has difficulty concentrating on tasks for long periods of time. Also, s/he has tendencies to become excitable and, well, hyperactive.
Characters with this affliction suffer a -2 penalty to any task that requires any bit of careful attention (exapmles: Concentration, Craft). By contrast, they receive a +2 bonus to any sort of physical activity (examples: Jump, Swim).
Just a random thought.