Post-lesional plasticity in the central nervous system of the guinea-pig: A "top-down" adaptation process?

Vestibular compensation for the postural and oculomotor deficits following unilateral labyrinthectomy is a model of functional plasticity in the brain of adult vertebrates, The mechanisms involved in this recovery are still c ontroversial.(6,11,17,18,24,27,30) The post-lesional lack of vestibular inp ut might be compensated by changes in the efficacy of the remaining sensory inputs involved in gaze and posture stabilization. However, the compensati on process could also rapidly become independent of these external cues, an d thus be detectable in vitro in preparations obtained from lesioned animal s. In agreement with this hypothesis, we have shown recently(28) that promi nent traces of the compensation process appeared three days after the lesio n on in vitro isolated brains taken from labyrinthectomized guinea-pigs, wh ere the connectivity of the central vestibular-related networks: is preserv ed. We report here that, one week after the lesion, a slight increase in th e intrinsic, spontaneous activity of the deafferented, central vestibular n eurons was found in brainstem slices, This increase became stronger in slic es taken after one month of compensation, and was associated at this stage with a significant decrease in the intrinsic activity of the vestibular neu rons on the contralesional side. Vestibular compensation could thus follow a "top-down" strategy: it would first rely on the external cues given by th e intact sensory systems, then on an internal reorganization of the vestibu lar-related networks, and finally on changes in the intrinsic properties of the vestibular neurons themselves. Similar strategies may be used by the m ammalian brain to compensate for other types of deafferentations or environ mental changes. (C) 1999 IBRO, Published by Elsevier Science Ltd.