Introduction: Unilateral spatial neglect (USN) is a disorder of contralesional space awareness which often follows unilateral brain lesion. Since USN impairs awareness of contralesional space/body and often of concomitant motor disorders, its presence represents a negative prognostic factor of functional recovery. Thus, the disorder needs to be carefully diagnosed and treated. Here, we attempted to present a clear and concise picture of current insights in the comprehension and rehabilitation of USN. Methods: We first provided an updated overview of USN clinical and neuroanatomical features and then highlighted recent progresses in the diagnosis and rehabilitation of the disease. In relation to USN rehabilitation, we conducted a MEDLINE literature research on three of the most promising interventions for USN rehabilitation: prismatic adaptation (PA), non-invasive brain stimulation (NIBS), and virtual reality (VR). The identified studies were classified according to the strength of their methods. Results: The last years have witnessed a relative decrement of interest in the study of neuropsychological disorders of spatial awareness in USN, but a relative increase in the study of potential interventions for its rehabilitation. Although optimal protocols still need to be defined, high-quality studies have demonstrated the efficacy of PA, TMS and tDCS interventions for the treatment of USN. In addition, preliminary investigations are suggesting the potentials of GVS and VR approaches for USN rehabilitation. Conclusion: Advancing neuropsychological and neuroscience tools to investigate USN pathophysiology is a necessary step to identify effective rehabilitation treatments and to foster our understanding of neurofunctional bases of spatial cognition in the healthy brain.

Prism adaptation (PA) has been applied with mixed success as a rehabilitation method of spatial neglect. Results from many single-case and multiple case studies as well as randomised controlled trials do not produce a clear picture of the efficacy of PA. We here tested a new method of PA, by inducing adaptation effects in the virtual reality. Healthy participants were attributed to one of four groups: no deviation, 10-, 20-, or 30-degrees rightward deviation. In contrast to classical wedge prisms, we induced the visual shift progressively. Participants performed two variants of the bisection and the landmark task to measure cognitive transfer of adaptation effects. Pointing error was directly related to the degree of optical deviation, and was greatest immediately following adaptation. Transfer was only observed in the bisection tasks, and only in the 30-degrees group. Due to the gradual induction of the spatial deviation the majority of participants were unaware of the adaptation effects. These findings show that large rightward deviation may affect sensorimotor performance in healthy participants similarly to neglect patients. Moreover, the finding that only participants adapted to 30-degrees showed biased bisection performance suggests that a critical threshold must be reached in order to induce significant visuomotor transfer.

During navigation, humans mainly rely on egocentric and allocentric spatial strategies, two different frames 37 of reference working together to build a coherent representation of the environment. Spatial memory deficits 38 during navigation have been repeatedly reported in patients with vestibular disorders. However, little is known 39 about how vestibular disorders can change the use of spatial navigation strategies. Here, we used a new reverse 40 T-maze paradigm in virtual reality to explore whether vestibular loss specifically modifies the use of egocentric 41 or allocentric spatial strategies in patients with unilateral (n = 23) and bilateral (n = 23) vestibular loss 42 compared to healthy volunteers matched for age, sex and education level (n = 23). Results showed that the 43 odds of selecting and using a specific strategy in the T-maze was significantly reduced in both unilateral and 44 bilateral vestibular loss. An exploratory analysis suggests that only right vestibular loss decreased the odds of 45 adopting a spatial strategy, indicating a functional asymmetry of vestibular functions. When considering 46patients who used strategies to navigate, we observed that a bilateral vestibular loss reduced the odds to use of 47 an allocentric strategy, whereas a unilateral vestibular loss decreased the odds to use of an egocentric strategy. 48Age was significantly associated with an overall lower chance to adopt a navigation strategy and, more 49 specifically, with a decrease in the odds of using an allocentric strategy. We did not observe any sex difference 50 in the ability to select and use a specific navigation strategy. Findings are discussed in light of previous studies 51 on visuo-spatial abilities and studies of vestibulo-hippocampal interactions in peripheral vestibular disorders. 52We discuss the potential impact of the history of the disease (chronic stage in patients with a bilateral 53 vestibulopathy vs. subacute stage in patients with a unilateral vestibular loss), of hearing impairment and non-54 specific attentional deficits in patients with vestibular disorders.