Age-related differences in corticomotor facilitation indicate dedifferentiation in motor planning

Efficient motor control requires motor planning. Age-related changes in motor control are well described, e.g. increased movement variability and greater antagonistic muscle co-activation, as well as less functional and less regional specific brain activation. However, less is known about age-related changes in motor planning. By use of transcranial magnetic stimulation we investigated differences in corticomotor facilitation during motor planning in 17 young (25±3years) and 17 older healthy adults (70±13years) in a delayed movement paradigm for wrist movements. Motor evoked potentials (MEPs) were recorded for the flexor and extensor carpi radialis during movement preparation of wrist flexion and extension as well as during rest. We found that MEPs were less specifically facilitated during planning in older as compared to younger adults, as indicated by an Age×Condition×Muscle interaction. Young participants showed significantly facilitated MEPs in the respective muscle needed for wrist flexion or extension. By contrast MEPs in older participants were less specifically modulated. We conclude that age relates to dedifferentiated activation of the primary motor cortex already during preparation of distinct movements which might contribute to less efficient motor control in older adults.