Vestffiular Recruitment and Decruitment

Abstract

Serial Thermal Vestibulometry with the application of increasing caloric stimuli (corresponding to decreasing temperature of water at successive irrigation of the ears) was performed on normal subjects and patients with lesions in the central nervous system involving the statoacoustic subsystem. The normal values and 'slope' values (i.e. increase in degrees of velocity of slow component of nystagmus in response to each 4°C change in water temperature) were computed to yield values of the normal vestibulogram. The values obtained in patients were compared with those of the Normograms and the following diagnostic patterns observed: (a) Hypograms, (b) Hypergrams, (c) Central Vestibular Recruitment, and (d) Central Vestibular Decruitment. Central Vestibular Recruitment has been explained on the basis of the locus of the lesion leading to involvement of the nystagmogenic area in the lower part of the reticular formation, supra-segmental neurones in the vicinity of the vestibular nuclear complex, and partial destruction of the complex itself, each being responsible alone or in combination. Hypergrams presumably result from suprasegmental lesions, e.g. in cerebrum, cerebellum and stem components. Central decruitment follows neural lesions in the vestibular subsystem. Hypograms are found in vestibular nuclear pathology. Furthermore, it helps in charting a plan for therapy, viz. head and balance exercises, in particular, in the sense that this exercise is not helpful in cases with central decruitment but is in peripheral one. An explanation for this has been put forward.