Effects of high and low dosages of methylphenidate in children with strong and sensitive nervous systems

This investigation was undertaken to explore the possible causes and consequences of the finding that attention-and learning-disordered children with sensitive (weak) nervous systems were titrated at higher dosages of methylphenidate than those with strong nervous systems. Pretreatment parent and teacher ratings of hyperkinetic-associated behavior were no different for children typed as having strong or sensitive nervous systems or for those subsequently prescribed higher or lower dosages by a child psychiatrist "blind" to their type as well as condition (drug or placebo). However, those titrated at lower dosages, regardless of whether strong or sensitive, were rated as more improved than those given higher dosages. Pretreatment reaction time (RT) data suggested that sensitive types prescribed low dosages had less of a problem sustaining attention, and placebo RT data suggested that strong types titrated at low dosages had more of a problem sustaining attention. A contrast of placebo and drug RTs showed that strong types titrated at lower dosages improved more than strong types given higher dosages, whereas sensitive types given higher dosages improved more than sensitive types given lower dosages. The latter finding is thought to add support to the theory of Gray (1964), who suggested that, paradoxically, the weak nervous system needs a more intense stimulus than the strong to reach the concentration threshold.