A finger-tapping test requiring rhythmic responses to frequencies from 1 to 6Hz was performed in 27 children (21 males, 6 females; aged 6 to 14 years, mean 11 years) diagnosed with ADHD, and in 33 controls at the Shaare Zedeck Medical Center, Jerusalem, Israel. Patients treated with methylphenidate (n=22) received no medication on the day of the test. Simultaneous computer-generated visual and auditory stimuli were presented at different frequencies over a 7-minute session. Children with ADHD responded at a faster rate than the stimulus, unlike control subjects who tapped in tandem with the stimulus. Fifteen of 27 children with ADHD demonstrated the “hastening” phenomenon (a tendency to exceed the stimulus frequency at the higher frequencies), compared to only 2 of the 33 controls (p<0.05). Children demonstrating the hastening response made recurrent errors in tapping, their responses were faster than controls, and the response frequency was constant (mean 3.8Hz, range 2.8-4.7Hz) regardless of the stimulus. Age and fast tapping responses for ADHD children were correlated inversely (p<0.05). The hastening phenomenon was not correlated with sex or handedness. [1]

COMMENT. This hastened voluntary response, termed hastening phenomenon, is also characteristic of patients with Parkinsonism. It may reflect an abnormal oscillatory mechanism mediated by dopaminergic frontal-striatal circuits that is released by cortical inhibitory frontal lobe deficits peculiar to ADHD. The authors propose that children with ADHD can follow slow rhythmic stimuli but at higher frequencies, their voluntary motor response is deranged by a disturbed central oscillatory mechanism. Impairments of handwriting and typing skills, both rhythmic voluntary movements, are often affected in ADHD and may be amenable to therapeutic intervention. Dysgraphia is frequently responsive to methylphenidate (MPH) as an adjunct to coordination exercises. (Millichap, 1973). The effect of MPH on the hastening phenomenon would be of interest.

A dose-response study of OROS-MPH showed that increasing doses (36-54 mg) were associated with a clear dose-response relationship, with improvements in 66-75% of ADHD-CT children. Parent ratings were more sensitive than teacher ratings. In children with ADHD-PI, improvements in attention occurred at lower doses, and less benefit was derived from higher doses. In both ADHD subtypes, higher doses were associated with increased insomnia and decreased appetite [2]. Biederman J reports that 54 mg of OROS-MPH (Concerta) is equivalent to 20 mg Adderall XR. [3]