Left neglect dyslexia, unilateral spatial neglect and the effects of sensory and transcranial stimulations

Left neglect dyslexia (ND) is a component deficit of the syndrome of spatial unilateral neglect (USN) that is frequently associated with manifestations of USN outside the reading domain, conjuring up a double dissociation of deficits, and prima facie suggesting the independence of these putative discrete components of USN. However, while the number of right-brain-damaged patients with left USN without ND is quite sizeable across studies, right-brain-damaged patients with left ND without any other manifestation of left USN are quite rare, some with bilateral damage, one with a developmental disorder. This asymmetry supports the suggestion that ND is an intrinsic component of extra-personal USN, that shares with it most of the affected processes and representations of near extra-personal space. In line with this conclusion, the severity of left ND has been repeatedly found to be related with that of other manifestations of extra-personal USN, outside the reading domain. Furthermore, the sensory lateralized stimulations (caloric and galvanic vestibular, visual optokinetic, neck muscle vibration, head and trunk rotation, visuo-motor adaptation to optical prisms that displace the visual scene laterally), and transcranial magnetic stimulations of the brain, overall modulate left ND, as other manifestations of extra-personal USN. ND may be temporarily improved, worsened or left unchanged, according to the directionality of the stimulation. These effects appear to involve primarily egocentric/viewer/centred representations of written material, both lexical and non-lexical in nature (words, nonwords, text). Importantly, results from experimental, single session, paradigms, have been used to develop successful rehabilitation paradigms of ND.