S14-2. F wave and spinal excitability; masseteric contraction or motor imagery enhances ulnar nerve F wave

Abstract

We tested the validity of instructing patients to clench the teeth to facilitate F-waves recorded from a limb muscle in clinical practice. We explored to study effect of motor imagery and voluntary contraction of the masseter muscles on F waves recorded from the first dorsal interosseous muscle in healthy subjects. F waves were recorded at rest, during motor imagery and during voluntary contraction monitored by a force transducer to maintain the level at 10% of maximal effort. F-wave persistence increased from at rest to during motor imagery, and during voluntary contraction. The trial average of F-waves increased from at rest to during motor imagery and during voluntary contraction. The F-wave latency revealed no significant changes. We have previously shown that motor imagery or slight voluntary contraction of the target muscle enhances F-wave persistence. The current study indicates the same process involving a non-target muscle can also cause a transient increase in distant motoneuron excitability, similar to Jendrassik maneuver. Central drive directed to the masseteric motoneurons can enhance the excitability of ulnar nerve anterior horn cells as evidenced by an increase of trial average of F-wave amplitudes.