| Summary: | Traditionally neuropsychological observations have constrained the view that semantic knowledge is organized in categories: animals, plants or tools (Warrington & Shallice, 1984; Caramazza & Shelton, 1998; Tyler & Moss, 2001). Recently it has suggested that social groups, defined as categories of individuals that share category-relevant characteristics and/or features (Mason & Macrae, 2004),could have a representation of their own. Rumiati et al. (2014) documented double dissociations on word sorting tasks between living things, non-living things and social groups in patients with primary dementia. Consistently with this neuropsychological finding, a neuroimaging study showed that, relatively to non-social concepts, concepts about social groups activated the medial prefrontal cortex, posterior cingulate, and the temporo-parietal junction (Contreras et al., 2012). In the present study we tested whether social groups, such as “Muslims” or “fat people”, are represented independently of the other concepts and, if so, what are their brain correlates. Twenty-nine patients with temporal and frontal brain tumors, either in the left or right hemisphere, and 19 healthy controls matched for age and education (all p> .05) were tested on three tasks (picture naming, word-to-picture-matching, and picture sorting) using stimuli that belonged to three categories: living things (animals and plants, N=15), non-living things (artifacts, N=15) and social groups (N=15). The stimuli belonging to the three categories were matched for letter length and frequency (all p> .05). Results showed that left-brain tumor patients (lBTP) were found to be worse than both healthy controls (HC) and right-brain tumor patients (rBTP) on naming non-living things (p<.05) and social groups (p<.01). lBTP performed significantly worse on naming non-living things than living things and social groups, while rBTP performed as well as healthy controls. Moreover lBTP made significantly more semantic errors and circumlocutions only with social groups category than rBTP who, in turn, made more visual errors. All the patients performed at ceiling level on both the word-to-picture-matching and picture sorting tasks. Voxel-based lesion-symptom mapping (VLSM) revealed that lesions involving the left inferior frontal gyrus led to a selective impairment in naming living things, lesions of the inferior temporal cortex led to a selective impairment in naming non-living things, and lesions of the area between the left inferior and middle frontal gyri led to a selective deficit in naming social groups. Thus the lesion analysis confirms that the social groups are represented independently of other concepts. Moreover, the brain regions, that when damaged give rise to a deficit in naming social groups, are comparable to those found activated in imaging findings dealing with social stereotypes.
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