The sense of balance and depth perception are at the basis of survival behaviors that are still not well understood: the fear of falling, and of heights. It is known that perceptual integration of depth occurs in the vestibular system, and in particular in the deep vestibular nuclei, a sensory-motor integration hub controlling posture and balance during walking (Angelaki and Cullen, 2008). But recent researches has revealed that the brainstem nuclei are far from being primitive, each nucleusprojecting directly to structures belonging to the subcortical network of emotion (Anderson and Adolphs, 2014). These emotional networks control behaviors that are thought to optimize the survival of individuals in dangerous situations: from the rapid coordination of instinctive defensive behaviors (flight or freezing responses, associated with physiological changes such as modulation of heart rate or respiration), to the coordination of persistent emotional states, such as anxiety or fear.
In this context, vestibular clinicians and psychiatrists have already reported for several years that a strong comorbidity exists between vestibular and psychiatric patients (Balaban et al., 2011; Staab, 2016): 30-50% of vestibular patients are affected by affective, psychological and psychiatric pathologies such as anxiety disorders in cases, depressive syndromes, or even states close to post-traumatic syndrome. This is reciprocal, as pre-existing psychiatric conditions are sometimes a predictor of the development of vestibular pathologies (Staab, 2016). We are therefore beyond the hypothesis of the existence of a vestibulo-emotional integration system, but rather facing a clinical reality.

From this point of view the fear of heights protects individuals from potentially painful or even fatal falls. These defensive behaviors require the coordinated activity of vestibular and emotional systems to respond to an imminent fall threat, but also to prepare the organisms to it, and to optimize its response. However to date, the brain networks controlling these vestibulo-emotional interactions remain to be revealed and understood.