Excitability of Spinal Neurons During a Short Period of Relaxation Imagery

To study spinal neuron function during relaxation imagery, we analyzed F-waves of the left thenar muscles in 15 healthy subjects (9 males, 6 females; mean age, 27.9 ± 9.2 years) after stimulating the left median nerve at the wrist. F- waves were recorded in a resting position and during and after a 1-min period of relaxation imagery; they were recorded immediately after and at 5, 10, and 15 min after the relaxation imagery period. Persistence, F/M amplitude ratio, and la- tency were analyzed from the recorded F-waves. No significant differences were observed in the abovementioned parameters obtained at rest, during, or after relaxation imagery (at any time points). However, the F/M amplitude ratio, as an index of spinal neuron excitability, was used to separate subjects into those with lower excitability, unchanged excitability, and higher excitability than the resting F/M ra- tios. In our subjective evaluation of the relaxation imagery methods, almost all subjects in the lower excitability group said they performed "relaxation imagery of the hand and thumb." In the higher excitability, almost all subjects said they performed "relaxation imagery of the whole body." These results indicate that a 1-min period of relaxation imagery does not change the excitability of spinal neurons in healthy subjects. However performing relaxation imagery focused on decreasing muscle tone in a specific area may de- crease the excitability of spinal neurons.