Análisis de las Co-Fluctuaciones en los Reflejos Hoffman del Músculo Flexor Carpi Radialis en el Humano

Abstract

Introduction: The Hoffman Reflex is a tool that can be useful in determining connection patterns in the spinal cord. In this paper we study bilateral fluctuations in amplitude of reflexes recorded in flexor carpi radialis of both forearms in nine neurologically healthy human subjects. This work was done in order to investigate the possibility of synchronized fluctuations in the excitability of the motor nuclei between both upper limbs. This would allow us to infer the existence of groups of interneurons that command, regulate or synchronize this excitability. Material and methods: Experiments were performed in 9 neurologically healthy subjects who signed informed consent. The protocol was approved by the Ethics Committee of Escuela Superior de Medicina, IPN. To obtain H reflexes, rectangular pulses of constant current were applied with 1 ms duration, between 3 and 7 mA intensity, and frequency of 1 Hz. All 500 records were taken simultaneously from both flexor carpi radialis discarding the first 10 and using the remaining 490 for analysis. Recruitment curves were analyzed to infer background excitability level of motor nuclei. We also analyzed covariance in the amplitude of reflexes for each limb, and the cross covariance between both sides before and after randomizing the amplitudes obtained. Results: We observed that even when background excitability of both sides were different, the amplitudes of RHS fluctuate similarly. Conclusion: Regardless of differences in background excitability for each upper limb, there appears to be some neural circuitry coordinating bilateral variations in amplitude of reflexes. This is consistent with findings by other researchers in lower medular segments.