Impaired processing of conspecifics in Parkinson’s disease

Experimental evidence indicates that the inferior frontal gyrus (IFG) processes emotional/affective features crucial to elaborate knowledge about social groups and that knowledge of social concepts is stored in the anterior temporal lobe (ATL). We investigated whether knowledge about social groups is impaired in Parkinson's disease (PD), in which dysfunctional connectivity between IFG and ATL has been demonstrated. PD patients (N = 20) and healthy controls (HC, N = 16) were given a lexical decision task in a semantic priming paradigm: the prime-targets included 144 words and 144 pseudowords, each preceded by three types of prime ("animals," "things," "persons"). Out of these 288 prime-targets, forty-eight were congruent (same category) and 96 incongruent (different category). Out of 48 congruent prime-targets, 24 denoted social items and 24 nonsocial items. Thus, four types of trials were obtained: congruent social; congruent nonsocial; incongruent social; incongruent nonsocial. Congruent target-words were recognized better than incongruent target-words by all groups. The semantic priming effect was preserved in PD; however, accuracy was significantly lower in PD than in HC in social items. No difference emerged between the two groups in nonsocial items. Impaired processing of words denoting social groups in PD may be due to impairment in accessing the affective/emotional features that characterize conceptual knowledge of social groups, for the functional disconnection between the IFG and the ATL.