Differences in motor imagery strategy change behavioral outcome.

Kinesthetic motor imagery (KMI) involves imagining the feeling and experience of movements. We examined the effects of KMI, number visualizing, and KMI with number visualizing on the excitability of spinal motor neurons and a behavioral outcome measure in a pinch force task. Healthy participants (13 men and 8 women; mean age: 24.8 ± 5.5 years) were recruited. We compared the F-waves of the left thenar muscles after stimulating the left median nerve at the wrist during each motor imagery condition after a practice session. The KMI condition consisted of imagining muscle contraction, the number visualizing condition consisted of imagining the pinch force increasing numerically, and the KMI with number visualizing consisted of alternating between the KMI and imagining the pinch force increasing numerically. Before and after motor imagery, the time required to adjust to the target pinch force was compared. The time required to adjust the pinch force was shorter in the KMI with number visualizing condition than in the KMI and number visualizing conditions. There was no difference in the F/M amplitude ratio between each MI strategy condition, indicating the excitability of spinal motor neurons. Numerical information helped to improve the ability of participants to perform KMI.