Caudate nucleus and social cognition: neuropsychological and SPECT evidence from a patient with focal caudate lesion.

Most studies in social cognition have focused on developmental diseases or analyzed the consequences of acquired frontal lesions on the integrity of Theory of Mind (ToM), but, to our knowledge, none to date has addressed the eventual consequences of damage to the basal ganglia on ToM. To investigate the possible consequences of such lesions on social cognition, we tested a selected patient, MVG, a 44-year-old man with a focal caudate nucleus (CN) lesion following stroke. In the aftermath of this stroke, MVG shows loss of empathy and difficulties recognizing emotions in others. The dual aims of this study were first, to evaluate the implications of CN on ToM and recognition of emotion, and second, to discuss these results as a consequence of a disconnection of the sub-cortical orbito-frontal (OF) loop due to caudate damage. We performed a complete neuropsychological assessment of MVG, as well as different tasks evaluating social cognition, such as the Faux-Pas Test and the Reading the Eyes in the Mind Test. No deficits were found in the neuropsychological tests. However, on tasks assessing social cognition, MVG showed impairments in the "warm" or "affective" part of ToM as well as in the ability to recognize negative emotions (i.e., sadness and fear). These results indicate that damage to the head of the left CN can lead to impairment of ToM and emotion recognition. Furthermore, the data shows that, in MVG, such impairment appears to be due to a disconnection of the sub-cortical OF circuit resulting from damage to the CN. Neuro-imaging data tends to confirm this hypothesis by bringing out a hypo-perfusion in both, the territory of his left CN and prefrontal (i.e., ventromedial) brain areas.