Coupling and Irregularity in the aging motor system: Tremor and movement

This experiment examined the hypothesis that aging reduces the coupling between system components, resulting in a loss of complexity in behavior. Young (18–23 years), old (60–65 years), and older old (70–75 years) subjects performed rhythmical movement and postural tasks with the index finger. Irregularity of the acceleration dynamics was lower during postural tremor and movement in the old and older old subjects, an age effect that was only observed on the mediolateral axis of motion. Coupling across the axes of motion was significantly higher during rhythmic movement in the elderly but remained unaltered across the tasks in the young adults. The results show that the loss of complexity with aging can be detected even in healthy 60–65-year-olds, but demonstrates the need for postural tremor to be examined on more than a single axis of motion. Our findings suggest that reduced motor adaptability with aging results from a greater demand on task-related reorganization of the motor output.