Does methylphenidate constrict cognitive functioning?

It has been suggested that stimulants enhance attention in children with (attention deficit disorder with hyperactivity) (ADDH) by producing a generalized constriction or "over-focusing." Such a phenomenon might be expected to adversely affect performance on tasks, such as those in the Wallach-Kogan (W-K) battery, which explicitly call for cognitive flexibility or "divergent thinking." Nineteen ADDH children, 6 to 10 years of age, were tested on two modified subtests of the W-K battery at baseline, following placebo, and following three different dosages (.3, .6 and 1.0 mg/kg) of methylphenidate. Contrary to the hypothesis, methylphenidate did not decrease but rather sustained output on the tests, which contrasted with a decline in productivity seen across nondrug days. Some ADDH subjects displayed particularly large increases in output following methylphenidate and may represent an atypical subgroup of children who became overaroused on medication.