Valence as principal dimension of the semantic space in primary progressive aphasia semantic variant

Previous studies of the semantic variant of primary progressive aphasia have determined which word features render single words more vulnerable. Here, we applied a graph-based approach and modelled the pathological changes at the network level. In healthy individuals, the two principal dimensions for the organization of the word meaning network are concreteness and valence. Ten semantic variant of primary progressive aphasia cases (mean age 66 years, 6 female, Clinical Dementia Rating: 3 patients = 0; 6 patients = 0.5; 1 patient = 1) participated as well as 79 matched controls. A set of 32 words were selected a priori to cover a broad range of valence and concreteness. In a triad judgement task (total of 192 trials), three words were presented on the screen at the corners of a triangle. Participants had to select which word pair was most closely associated in meaning. Responses were analysed using multidimensional Bayesian scaling. In controls, the first principal dimension was determined by word concreteness (β = 0.39, P = 0.013) and valence (β = 0.34, P = 0.028) and the second by word dominance (β = 2.09, P = 0.0009) and arousal (β = -1.45, P = 0.009). In patients, the semantic network changed to a circumplex configuration with valence as the unique dimension (dimension 1: β = -0.72, P = 0.0005; dimension 2: β = 0.46, P = 0.006) and no effect of word concreteness. In the semantic variant of primary progressive aphasia, there is relative preservation of word valence as one of the organizational principles for the word network despite the loss of concreteness as organizing principle.