The vestibulospinal reflex in humans: effects on paraspinal muscle activity.

OBJECTIVE

To elucidate the electromyographic (EMG) patterns elicited in the superficial paraspinal muscles (sacrospinalis, ileocostalis lomborum, longissimus dorsi and splenium cervicis).

MATERIAL AND METHODS

In normal subjects adapted to the dark and standing on a force platform, EMG patterns were elicited in the superficial paraspinal muscles by means of unilateral cold caloric stimulation of the labyrinth.

RESULTS

Almost concomitantly with the occurrence of postural derangement of the subject's trunk and head, the EMG patterns of the paraspinal muscles on both sides showed significant and consistent changes. In particular, the paraspinal muscles ipsilateral to the stimulated side showed a significant reduction in activity, while the homologous muscles of the contralateral side markedly increased their activity, with a consistent delay in comparison to the contralateral muscles. Moreover, the EMG changes occurred in a hierarchic fashion in the caudal-rostral direction. In fact, the more powerful and longer-lasting effects were consistently observed in the more caudal muscles, i.e. the sacrospinalis and ileocostalis, while the effects on the longissimus dorsi and splenium cervicis muscles were weak and inconsistent.

CONCLUSION

These results suggest a possible use for the EMG patterns resulting from unilateral cold caloric stimulation for clinical evaluation of the vestibulospinal reflex.