Catherine Merck

Distinct neural substrates of affective and cognitive theory of mind impairment in semantic dementia.

ABSTRACT Using structural MRI, we investigated the brain substrates of both affective and cognitive theory of mind (ToM) in 19 patients with semantic dementia. We also ran intrinsic connectivity analyses to identify the networks to which the substrates belong and whether they are functionally disturbed in semantic dementia. In line with previous studies, we observed a ToM impairment in patients with semantic dementia even when semantic memory was regressed out. Our results also highlighted different neural bases according to the nature (affective or cognitive) of the representations being inferred. The affective ToM deficit was associated with atrophy in the amygdala, suggesting the involvement of emotion-processing deficits in this impairment. By contrast, cognitive ToM performances were correlated with the volume of medial prefrontal and parietal regions, as well as the right frontal operculum. Intrinsic connectivity analyses revealed decreased functional connectivity, mainly between midline cortical regions and temporal regions. They also showed that left medial temporal regions were functionally isolated, a further possible hindrance to normal social cognitive functioning in semantic dementia. Overall, this study addressed for the first time the neuroanatomical substrates of both cognitive and affective ToM disruption in semantic dementia, highlighting disturbed connectivity within the networks that sustain these abilities.

Relative category-specific preservation in semantic dementia? Evidence from 35 cases

Category-specific deficits have rarely been reported in semantic dementia (SD). To our knowledge, only four previous studies have documented category-specific deficits, and these have focused on the living versus non-living things contrast rather than on more fine-grained semantic categories. This study aimed to determine whether a category-specific effect could be highlighted by a semantic sorting task administered to 35 SD patients once at baseline and again after 2 years and to 10 Alzheimers disease patients (AD). We found a relative preservation of fruit and vegetables only in SD. This relative preservation of fruit and vegetables could be considered with regard to the importance of color knowledge in their discrimination. Indeed, color knowledge retrieval is known to depend on the left posterior fusiform gyrus which is relatively spared in SD. Finally, according to predictions of semantic memory models, our findings best fitted the Devlin and Gonnermans computational account.

Towards a left MTL specialization for arbitrary-associative learning? A multiple-case study

Since the famous case of HM provided unquestionable evidence for the involvement of medial temporal lobe (MTL) structures in memory, a dominant neuropsychological model raised up in the 1970’s. Brenda Milner proposed that “the most significant variable (to explain post-surgery memory outcome in temporal lobe epilepsy) is the verbal or non-verbal character of the material to be retained” [1]. This model predicts that verbal and non-verbal memories are homogenous and independent systems, respectively relying upon left and right temporal lobes. Yet, series of cases of amnesia following unilateral temporal lobectomy have been documented, drawing a more complex picture [2]. Moreover, cases of poorer verbalmemory outcome after right TL surgery had been reported [3], and other studies underlined deficits in spatial learning after left surgery. Taken together, those data strongly challenges the dominant material-specific view. In linewith those challenging data,other authors suggested that beyond material-specificity, task-specifi-

Does the left posterior fusiform gyrus play a critical role in fruit and vegetables categorization? Evidence from 19 semantic dementia patients

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Does the left posterior fusiform gyrus play a critical role in fruit and vegetables categorization? Evidence from 19 semantic dementia patients Catherine Merck, Isabelle Corouge, Pierre-Yves Jonin, Béatrice Desgranges, Jean-Yves Gauvrit, Serge Belliard