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Stefania Bracci, Magdalena Ietswaart, Cristiana Cavina-Pratesi; Giving the brain a hand: Evidence for a hand selective visual area in the human left lateral occipito-temporal cortex. Journal of Vision 2010;10(7):948. doi: 10.1167/10.7.948.
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There is accumulating evidence for a “map” of brain areas specialized to represent and process specific categories of stimuli. Evolution may have played a significant role in shaping such specializations for particular categories. For example, stimuli which have played a critical role in social adaptive behaviour such as bodies and faces have dedicated cortical representations in visual cortex: extrastriate body area (EBA) and fusiform face area (FFA), respectively. The human hand with its unique structure (e.g., finger-thumb opposition) has played a major role in human evolution, and is thus a prime candidate to be represented by a specialised brain area in the visual cortex. Using functional magnetic resonance imaging (fMRI), we provide the first evidence for a brain area selective for the human hand. In our study, 14 right handed participants looked at 8 different categories of stimuli (whole-bodies, body-parts, hands, fingers, feet, robotic-hands, tools and chairs) and performed the one-back task. The hand-selective area was found in all participants within the lateral occipital sulcus and so we name this area the Lateral Occipital Hand Area (LOHA). LOHA responds more to hands compared to body stimuli and it is anatomically separated from body selective areas (e.g., EBA). In addition, LOHA responds more to hands compared to i) hand parts (fingers), ii) other single body parts (feet) and iii) stimuli sharing functional traits with hands (robotic hands). These findings suggest that LOHA is specialized for representing and processing the shape of the human hand as a whole. Remarkably, in contrast with other body-selective sites, which are primarily lateralized in the right hemisphere (EBA and FFA), LOHA is localized in the left hemisphere. Overall, our study sheds further light on the functional organization of the human visual system and brings new evidence in support of the domain-specificity theory for visual object recognition.
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