Ipsilesional disruptions to reciprocal finger tapping.

Impairments in repetitive finger tapping have not been found in the ipsilesional hand, possibly because the performance measure (tapping rate) which has been used is not sufficiently sensitive. In this study, tapping performance of patients with lateralized brain damage was examined using more detailed measures reflecting intertap variability and the relative timing of each tap cycle. In concert with previous findings, neither the left- nor the right-hemisphere-damaged patients exhibited an impairment in tapping rate. An impairment in tapping variability was observed, however, but only for the left hemisphere group. It is argued that intertap variability may be particularly sensitive to left hemisphere damage as this measure reflects the demands for rather precise and consistent phasing or sequencing of muscle activation. Since left hemisphere damage often leads to deficits in making transitions between movements in a sequence, the consistent sequencing of agonist-antagonist muscle activations in tapping may be compromised. Future research directions to examine this hypothesis are discussed.