Characterizing the developmental profile of effort-induced motor overflow across a timed trial

Motor overflow is overt involuntary movement that accompanies voluntary movement. This study investigated the change in overflow production across a timed trial and the factors that affected this profile. Seventeen children (aged 8-11 years), 17 young adults (aged 18-35 years), and 17 older adults (aged 60-80 years) performed a 5-s finger pressing task by exerting 33% or 66% of their maximal force output using either index finger. Overflow was recorded as force from the alternative index finger. Young adult overflow remained stable over the 5 s. The rate of overflow increase over time was significantly greater for children than young adults. There was also a tendency for a greater overflow increase in older adults than in young adults. This overflow gradient was also greater in the right hand, particularly for children. These findings indicate that the neurological processes underlying overflow production are age dependent. Overflow progressed in a dynamic fashion over the course of a trial in children and older adults, probably because of increased bilateral cortical activation and the facilitation of motor task performance. This study is unique in quantitatively capturing the dynamic profile of overflow production in healthy participants across the life span.