Neglect: a multisensory deficit?

Neglect is a neurological syndrome characterised by a lack of conscious perception of events localised in the contralesional side of space. Here, we consider the possible multisensory nature of this disorder, critically reviewing the literature devoted to multisensory manifestations and processing in neglect. Although its most striking manifestations have been observed in the visual domain, a number of studies demonstrate that neglect can affect virtually any sensory modality, in particular touch and audition. Furthermore, a few recent studies have reported a correlation in severity between visual and non-visual neglect-related deficits evaluated in the same patients, providing some preliminary support for a multisensory conception of neglect. Sensory stimulation and sensorimotor adaptation techniques, aimed at alleviating neglect, have also been shown to affect several sensory modalities, including some that were not directly affected by the intervention. Finally, in some cases neglect can bias multisensory interactions known to occur in healthy individuals, leading to abnormal behaviour or uncovering multisensory compensation mechanisms. This evidence, together with neurophysiological and neuroimaging data revealing the multisensory role played by the areas that are most commonly damaged in neglect patients, seems to speak in favour of neglect as a multisensory disorder. However, since most previous studies were not conducted with the specific purpose of systematically investigating the multisensory nature of neglect, we conclude that more research is needed to appropriately assess this question, and suggest some methodological guidelines that we hope will help clarify this issue. At present, the conception of neglect as a multisensory disorder remains a promising working hypothesis that may help define the pathophysiology of this syndrome.