Modulatory Effects of the Motor Imagery and Jendrassik Maneuver upon the Forearm H-Reflex and Electroencephalographic Activity

While the Jendrassik maneuver (JM) is commonly used in neurology to enhance monosynaptic reflexes such as the knee-jerk reflex, its interaction with cognitive processes like motor imagery (MI) remains unclear. In this study, we examined the effects of JM, MI, and their combination on the left flexor carpi radialis (FCR) H-reflex and cortical electroencephalographic (EEG) activity. Twenty healthy participants completed four tasks: resting, MI (imagining squeezing a tennis ball with the left hand), JM (squeezing a tennis ball with the right hand), and JM combined with MI (JM&MI). The FCR H-reflex was elicited with median nerve stimulation, and EEG changes were analyzed through event-related potentials and modulations of the mu rhythm. Surprisingly, JM performed with the right hand did not affect the contralateral H-reflex. MI of the left hand decreased the H-reflex in the right FCR. JM and MI significantly modulated cortical activity. Event-related desynchronization (ERD) of the mu-rhythm occurred during both JM and MI, and it was contralateral to the physical contraction or imagery. Bilateral ERD was observed during JM&MI. Cortical responses to nerve stimulation (P100, N100 and P300 components) varied by task, and during JM the P100 and P300 components correlated with strength of mu-rhythm ERD.