The purpose of this study was to investigate the effect of motor imagery on the premotor time (PMT). Twelve healthy adults performed reaction time movements in response to external visual signals at rest, when holding an object (muscle activation), or performing different background imagined movements (motor imagery). When compared to rest, muscle activation reduced the PMT; imagined finger extension of the right hand and imagined finger flexion of the left hand elongated the PMT; imagined finger flexion of the right hand had no effect on the PMT. This movement-specific effect is interpreted as the sum of the excitatory effect caused by enhanced corticospinal excitability specifically for the primary mover of the imagined movement and an overall inhibition associated with increased task complexity during motor imagery. Our results clearly demonstrate that motor imagery has movement-specific effects on the PMT.
Li is with the Dept of Physical Therapy, University of Montana–Missoula, Missoula, MT 59801. Stevens is with the Dept of Psychology, College of William & Mary, Williamsburg, VA 23187. Kamper and Rymer are with the Dept of Physical Medicine and Rehabilitation, Northwestern University, Chicago, IL 60611 and the Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL 60611.