Effects of clinical dosage levels of methylphenidate on two-flash thresholds and perceptual motor performance in hyperactive children.

S?immnry.-Three groups (ns = 10) of children (normals, hyperactives, hyperactives on medication) were administered eight perceptual-motor tasks. The normal controls were significantly superior in performance in comparison wich the hyperactives taken off methylphenidate on rhree tasks but only superior on one task (Digit Symbol) when compared to hyperactives on methylphenidate. The hyperactives on medication were also significantly superior to the hyperactives not on medication on the Digit Symbol task. The purpose of this study was to investigate the effects of clinical dosage levels of methylphenidate and its discontinuance on the two-flash thresholds and perceptual-motor performance of hyperactive children. There is considerable evidence for increase in abiliry to concentrate and in attention span in hyperacrive children following administration of merhylphenidate (e.g., Barkley, 1976; Spring, Yellin, & Greenberg, 1976). Brodemus and Swanson (1977-78) proposed that the "paradoxical effects" of stimulant drugs on hyperactive children results from providing necessary internal stimulation and consequently reducing the need for external stimulation. This input reportedly results in central nervous system arousal and a consequent decrease in hyperactive behavior. One would expect that such changes would also lead ro a lowering of perceptual thresholds. Fehr and Sprague (1969) present suggestive evidence for a temporary raising of two-flash thresholds following discontinuation of methylphenidate in hyperacrive children. The rhree groups of subjects were 10 normal controls. 10 hyperactive children on clinical dosages of methylphenidate. and 10 hyperactive children taken off methylphenidate at least six weeks. The range of medication dosage level and frequency was 5 m, once a day (total = 5 m) to 30 m, three times a day (total = 90 m). The hyperactive subjects off medication had had their clinical dosages routinely discontinued for a summer hiatus; the other hyperacrive subjects were from the same clinical population but tested before their routine summer drug hiatus. The mean age for the 30 male subjects was 10.3 yr. (SD = 1.2). with no significanr differences in age among the rhree groups. Each subject was administered the two-flash threshold by a method of limits technique. The perceptual-motor tests administered were the Finger Tapping Test (motor speed in right and left hands), Trail Making Test A and B (simple and complex visual search), WISC-R Digit Span forwards and backwards (auditory attention), and the WISC-R Digit Symbol (complex psychomo:or task). Table 1 presents means and standard deviations on the eight measures for the three groups. The analysis (t tests. all wich df = 18) yielded no significanr differences among the three groups on two-flash threshold performance. However. the two-flash threshold was significantly (p 6 .05) correlated with all of the perceptual-motor measurFs except Digit Span-backwards. The correlations with the two-flash thresholds were .50 (Trails A), .40 (Trails B) , -.53 (Tapping-right) . -.57 (Tapping-left) , -.53 (Digit Span-forward), -.27 (Digit Span-backwards), and -.38 (Digit Symbol). The relationships were all in the direction of low thresholds associating with good performance