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SPATIAL NEGLECT

Abstract

Giuseppe Vallar, MD, specialty in Neurology, Italian, was born in Milan. Department of Psychology, University of Milano-Bicocca, & IRCCS Italian Auxological Institute, Milan, Italy. Email: giuseppe.vallar@unimib.it

Giuseppe Vallar since 1999, Professor of Psychobiology and Physiological Psychology and, since 2009, the Director of the Specialty School in Neuropsychology, of the Department of Psychology of the University of Milan-Bicocca-Milan, Italy. Since 2005 Giuseppe Vallar is the Head of the Neuropsychological Laboratory, of the Italian Auxological Institute, Saint Luca Hospital, Milan, Italy. Previously, Giuseppe Vallar has been: (i) Professor of Psychobiology and Physiological Psychology in the Faculty of Psychology, Department of Psychology, of the University of Rome “La Sapienza”, Rome, Italy (1995–1999); (ii) Associate Professor of Psychology in the same University; (iii) Assistant Professor (Research) in the Faculty of Medicine, of the II Neurological Clinic of the University of Milan, Italy (1980–1992). Previous main institutional responsibilities include: (i) Dean of the Faculty of Psychology of the University of Milan-Bicocca (2001–2007), (ii) President of the Conference of the Deans of the Italian Faculties of Psychology (2006), (iii) Coordinator of the Phd Program in Psychology, Linguistics, and cognitive Neurosciences of the Department of Psychology of the University of Milan-Bicocca (2001–2006), (iv) Founding President of the Società Italiana di Neuropsicologia (SINP (1997–2001).

The syndrome of unilateral spatial neglect is one of the most disabling neuropsychological deficits caused by brain damage, most frequently in the right cerebral hemisphere. Neglect affects over 60% of right-brain-damaged patients, particularly in the acute phase after stroke. The manifestations of neglect are manifold, and may occur independent of each other, but all of them share a divide, which distinguishes the neglected (namely, not explored, where events are undetected) from the non-neglected side of space. Clinical manifestations include not only “deficits” (such as impaired search and report of events), but also gratuitous (not required by the environmental set) productions, as perseveration behaviour of varying complexity. Different sectors of space may be selectively affected: one main distinction concerns extra-personal vs. personal, bodily space.

Patients may neglect the side of the body contralateral to the lesion, hence, after right-brain damage, the left side. Neglect for the left side of the body includes simple “defective” impairments (personal hemi-neglect, hemi-asomatognosia), and more “complex” productive delusional belief (somatoparaphrenia) concerning left body parts (most frequently, though not exclusively, the left hand). These delusions may be variably florid, ranging from the mere disownership of the left hand, to the misattribution of its ownership to another person, with a variety of arguments. These patients may be also unaware of left-sided sensori-motor deficits (anosognosia for hemiplegia, hemianesthesia, hemianopia), and this unawareness may occur independent of hemi-asomatognosia and somatoparaphrenia.

Notwithstanding the prima facie higher-level (cognitive) features of these disorders of body knowledge, the relevant neuro-functional representation of the body is mostly, though not exclusively, based on the continuous integration and updating of multisensory signals, as revealed by the effects of direction-specific sensory stimulations (e.g., vestibular caloric) on these bodily manifestations of the neglect syndrome. Also, conditions, in which a conflict between senses (i.e., somatic sensation and vision, as in the Rubber Hand Illusion) is artificially created, may modulate the disownership symptom of somatoparaphrenia in brain-damaged patients, as well as shedding light into the neurofunctional mechanisms supporting the sense of ownership of body parts, and, more generally, of the bodily self, in unimpaired individuals.

The view that putatively lower-level processes, as multisensory integration, play a most important role in different aspects of the representation of the body, and of its parts, is in line with the increasing evidence that some basic homeostatic variables are modulated by cerebral cortical activity, and by sensorimotor information known to affect spatial and bodily representations.

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