Effects of methylphenidate on the fixed-ratio performance of mentally retarded children.

ABSTRACT

The effects of methylphenidate on the lever-pressing of 12 mentally retarded children maintained under fixed-ratio 5, 10 and 20 schedules of food delivery were examined. For five children, methylphenidate at oral doses of 0.3, 0.7 and 1.0 mg/kg produced generally dose-dependent decreases in response rates, whereas for the other seven children the two lower doses increased response rates while the highest dose decreased responding. The differential effects of methylphenidate across participants could not be attributed to differences in control response rates or demographic factors. However, each child whose rate of fixed-ratio responding was increased by methylphenidate also demonstrated a therapeutic response to the drug.