Spatial neglect--a vestibular disorder?

The phenomenon of spatial neglect after right brain damage greatly helps our understanding of the normal mechanisms of directing and maintaining spatial attention, of spatial orientation, and the characteristics of neural representation of space. The intriguing symptom is a spontaneous orientation bias towards the right leading to neglect of objects or persons on the left. Interestingly, we observe similar symptoms namely a spontaneous bias of eyes and head along the horizontal dimension of space in patients with unilateral vestibular dysfunction. Further similarities concern anatomical findings. Both spatial neglect and vestibular processing at cortical level show dominance in the right hemisphere and involve common brain areas. Lesion studies in human and monkey, electrical and transcranial magnetic stimulation, as well as functional imaging results have revealed the superior temporal cortex, insula and the temporo-parietal junction to be substantial parts of the multisensory (vestibular) system as well as to be affected in spatial neglect. We argue that these structures are not strictly 'vestibular' but rather have a multimodal character representing a significant site for the neural transformation of converging vestibular, auditory, neck proprioceptive and visual input into higher order spatial representations. Neurons of these regions provide us with redundant information about the position and motion of our body in space. They seem to play an essential role in adjusting body position relative to external space. This view may initiate further development of those strategies to treat spatial neglect that use routes to rehabilitation based on specific manipulations of sensory input feeding into this system.