Vestibular Contributions to Human Memory

The vestibular system is an ancient structure which supports the detection and control of self-motion. The pervasiveness of this sensory system is evidenced by the diversity of its anatomical projections and the profound impact it has on a range of higher level functions, particularly spatial memory. The aim of this thesis was to better characterise the association between the vestibular system and human memory; while many studies have explored this association from a biological perspective few have done so from a psychological one. In Chapter 1, evidence was drawn from 101 neuro-otology patients to show that vestibular dysfunction can exert a direct negative effect on memory and allied cognitive processes, independently of age and comorbid psychiatric and fatigue symptoms. In Chapters 3 and 4, the separability of these cognitive, psychiatric and fatigue symptoms was further demonstrated in eight traumatic brain injury patients who, following a programme of daily vestibular stimulation, showed cognitive improvement and electrophysiological modulation in the absence of psychiatric or fatigue-related changes. Finally in Chapter 5, a set of normative experiments indicated that, beyond any generic arousal effect (unspecific to any particular cognitive process), visual memory can utilise temporally coincident vestibular activation to help individuate one memory from another. Together these findings help clarify the range of and manner in which vestibular signals interact with visual short-term memory and allied cognitive processes. The findings also have clinical implications for the diagnosis and management of vestibular, neuropsychiatric and amnesic conditions.