Reading words and other people: A comparison of exception word, familiar face and affect processing in the left and right temporal variants of primary progressive aphasia

Abstract

Semantic variant primary progressive aphasia (svPPA) typically presents with left-hemisphere predominant rostral temporal lobe (rTL) atrophy and the most significant complaints within the language domain. Less frequently, patients present with right-hemisphere predominant temporal atrophy coupled with marked impairments in processing of famous faces and emotions. Few studies have objectively compared these patient groups in both domains and therefore it is unclear to what extent the syndromes overlap. Clinically diagnosed svPPA patients were characterized as left- (n = 21) or right-predominant (n = 12) using imaging and compared along with 14 healthy controls. Regarding language, our primary focus was upon two hallmark features of svPPA; confrontation naming and surface dyslexia. Both groups exhibited naming deficits and surface dyslexia although the impairments were more severe in the left-predominant group. Familiarity judgments on famous faces and affect processing were more profoundly impaired in the right-predominant group. Our findings suggest that the two syndromes overlap significantly but that early cases at the tail ends of the continuum constitute a challenge for current clinical criteria. Correlational neuroimaging analyses implicated a mid portion of the left lateral temporal lobe in exception word reading impairments in line with proposals that this region is an interface between phonology and semantic knowledge.

Keywords: Anterior temporal lobe; Primary progressive aphasia; Semantic dementia; Social cognition; Surface dyslexia.

Figure 1

Distribution of temporal lobe volume loss in left-predominant svPPA and right-predominant svPPA. (A) Illustration of the regions of interest (ROIs) in which mean percentage volume loss was calculated for each patient group. The caudal temporal lobe ROI features in dark grey with a black outline. The rostral temporal lobe (rTL) ROI was the combination of the white and black gyral ROIs. The gyral ROIs were used for a focused rTL analysis featured in the bottom two panels. (B) Rostral vs. caudal temporal lobe volume loss in the left and right hemispheres, by patient sub-group. (C) Gyral distribution of left rTL volume loss in left- and right-predominant svPPA. (D) Gyral distribution of right rTL volume loss in left- and right-predominant svPPA. * p<0.05 (error bars display one standard deviation). STG = superior temporal gyrus; MTG = middle temporal gyrus; ITG = inferior temporal gyrus; FG = fusiform gyrus; PhG = parahippocampal gyrus.

Figure 2

Patterns of atrophy in semantic variant PPA (svPPA). Voxel-based morphometry was used to identify regions of grey matter volume loss in svPPA relative to age-matched healthy controls (Row A), left predominant svPPA relative to controls (Row B), and right-predominant svPPA relative to controls (Row C; all p < 0.05, corrected for multiple comparisons). A direct comparison between the patient sub-groups (Row D) reveals greater volume loss in L-svPPA relative to R-svPPA (red-yellow color scale) and vice versa (blue-green color scale; p <0.001, uncorrected). Coronal slice positions are provided in standard stereotactic coordinates according to the Montreal Neurological Institute (MNI) protocol. L = Left; R = Right. HCi = Healthy (age-matched) controls for imaging analyses.

Figure 3

Brain regions associated with irregular word reading deficits in svPPA. Voxel-based morphometry was used to identify regions of grey matter atrophy that correlated with the regularity effect in reading performance (percentage of correctly read regular words minus percentage of correctly read irregular words) across all svPPA patients (p <0.001, uncorrected; minimum cluster size of 100 contiguous voxels).