Beyond the Non-Specific Attentional Effect of Caloric Vestibular Stimulation: Evidence from Healthy Subjects and Patients

Caloric vestibular stimulation (CVS) is a simple physiological manipulation that has been used for a long time in different clinical fields due to its rapid and relevant effects on behaviour. One of the most debated issues in this research field concerns the degree of specificity of such stimulation, namely whether the effects of CVS can be, and to what extent are, independent of the mere influence of non-specific factors such as general arousal, ocular movements or attentional shift towards the stimulated side. The hypothesis that CVS might cause a shift of attention towards the side of the stimulation has been largely supported; moreover, a large amount of evidence is available nowadays to corroborate the specific effect of CVS, providing behavioural and neurophysiological data in both patients and normal subjects. These data converge in indicating that the effects of CVS can be independent of eye deviation and general arousal, can modulate different symptoms in different directions, and do not merely depend on a general shift of attention. The present article is divided into three main sections. In the first section, we describe classical studies that investigate the effects of CVS on neglect and related symptoms. In the second and third parts, we provide an overview of the modulatory effects of CVS on somatosensory processes and body representation in both brain-damaged patients and healthy subjects. Finally, we conclude by discussing the relevance of these new findings for the understanding of the neural mechanisms underlying the modulatory effects of CVS.