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Article #40463
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Tamè L, Braun C, Holmes NP, Farnè A, Pavani F (2016) Bilateral representations of touch in the primary somatosensory cortex. Cognitive Neuropsychology, 33(1-2):48-66    
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Abstract
When coding the location of a tactile stimulus on the skin, the brain must be able to determine which side of the body was stimulated. Concurrently, the behavioural demands of dexterous and coordinated bimanual motor tasks require early integration of bilateral tactile information. This simultaneous requirement both for the disambiguation of the touched body side and the integration of touch across body sides is resolved by the entirely contralateral organisation of the somatosensory cortices, at least according to textbook perspectives. In this view, primary somatosensory cortices (SI) support contralateral tactile representations, whereas structures beyond SI, in particular the secondary somatosensory cortices (SII), support bilateral tactile representations. Growing evidence in the last decade, however, is forcing a revision of this textbook account. Studies in humans and other animals indicate that SI is more than a simple relay for contralateral sensory information and, together with SII, contributes to the integration of somatosensory inputs from the two body sides. Here, we review a series of recent works from our and other laboratories, supporting the existence of interactions between tactile stimuli on the two sides of the body at early stages of tactile processing. We begin by describing behavioural studies, in both healthy and brain-damaged humans that showed tactile interactions between body sides. Then we describe the neural substrates of bilateral interactions in somatosensation, as revealed by neurophysiological work in animals, and neuroimaging studies in humans (i.e., functional magnetic resonance, magnetoencephalography, and transcranial magnetic stimulation). Finally, we conclude by considering how the brain can achieve both body side disambiguation and bilateral integration as a function of task-demands, within the highly integrated somatosensory system