Mapping the neglect syndrome onto neurofunctional streams

The syndrome of unilateral spatial neglect (USN) is currently conceived as a multifarious deficit. This reflects, in turn, the multi-component structure of spatial representational/attentional processes, that are not monolithic in nature. A main dimension of the USN syndrome is along the premotor vs. perceptual distinction. The impairment of some USN patients may be confined to the planning, and execution of movements towards the contralesional, neglected, side of space. A main aspect of the disorder may be characterized, however, in terms of the defective perceptual awareness of contralesional, events, that may be, nevertheless, processed implicitly. Such an implicit processing ranges from semantic priming, lexical effects in reading, to preserved sensory illusions. From the neuropsychological vantage-point of USN, we take the view that the two visual streams dichotomy, both in the original version of Ungerleider and Mishkin ( 1982), and in the development by Milner and Goodale (1995 , this volume), captures only partially the neural loops concerned with perception and action in the visual domain. The USN syndrome suggests the existence of a neural system supporting perceptual awareness in spatial reference frames, for vision, and for other sensory modalities, as well as goal-directed, intentional action in the space surrounding us (Rizzolatti et al., 1997). A third, dorsal-ventral, stream, including the inferior parietal lobule, and the ventral premotor cortex (Gallese, 2007; Rizzolatti and Matelli, 2003) may constitute the neural underpinnings of spatial awareness for perception and action.