| The primary objective of this study was to determine the relative contributions of the proprioceptive and vestibular systems to the sense of velocity in the lumbar spine. For this study, an active training/active assessment lateral movement protocol was developed. It was hypothesized that altering vestibular and proprioceptive inputs, using galvanic and vibration stimulus respectively, would alter the sense of lateral trunk motion. Seventeen healthy subjects were recruited for the University of Kansas approved study. Two stimulus modalities were used independently. Transmastoidal bipolar galvanic vestibular stimulus was applied below the cutaneous threshold. Separately, an inertial vibratory stimulus device applied a 44.5Hz and .28g pk-pk acceleration to the left and right paraspinal muscle groups at the L3 level. Subjects performed lateral trunk flexion movements while lying prone with their pelvis fixed. With audible performance-based feedback provided during training, subjects matched target paces of 9.5, 13.5, and 17.5°/s. The protocol consisted of alternate training and assessment trials for each of five conditions per target speed. Subjects moved significantly slower overall but faster in the direction of vibration application. These results suggest that the muscle spindle organs were more sensitive to the applied vibration during lengthening than during shortening. There was a similar, though not statistically significant trend observed with the application of galvanic vestibular stimulus, possibly due to the test configuration. The illusory movement elicited in the spindle organs of the paraspinal muscles due to the local vibratory stimulus was shown to have a significant effect on magnitude and directionality of lateral trunk flexion velocity sense. These findings are a significant first step in understanding proprioceptive contributions to the control of trunk motion and stability. |
