A reevaluation of intervestibular nuclear coupling: its role in vestibular compensation.

Recent experimental observations indicate that pathways interconnecting the bilateral vestibular nuclei (VN) may provide positive-feedback loops for signals across the midline. The implications of such positive feedback are considered in the context of vestibular compensation. A simple conceptual model of the interconnected VN is studied analytically, based on the hypothesis that the restoration of central symmetry is achieved via changes of neural gain in closed commissural loops. A wide variety of experimental conditions related to vestibular compensation are investigated. Analytic model predictions are compared to behavioral and neurophysiological findings in the literature. The results show that organized control over commissural gains in closed loops coupling the bilateral VN is fully compatible with all phenomena cited in the article. In particular, such a mechanism for vestibular compensation can reconcile observations such as the fact that Bechterew phenomena and decompensation can both be elicited from the compensated state. Placing the site of vestibular compensation in pathways linking the VN has many implications. Other forms of central neural plasticity (e.g., vestibuloocular reflex (VOR) gain plasticity) may rely on a similar principle, since modulation of transmidline coupling can be a very powerful means of altering responses in a bilateral nervous system.