Reading disorders in primary progressive aphasia: A behavioral and neuroimaging study

Abstract

Previous neuropsychological studies on acquired dyslexia revealed a double dissociation in reading impairments. Patients with phonological dyslexia have selective difficulty reading pseudo-words, while those with surface dyslexia misread exception words. This double dissociation in reading abilities has often been reported in brain damaged patients, but it has not been consistently shown in patients with neurodegenerative diseases.In this study, we investigated reading impairments and their anatomical correlates in various neurodegenerative diseases. First, we performed a behavioral analysis to characterize the reading of different word types in primary progressive aphasia (PPA). Then, we conducted a voxel-based morphometry neuroimaging study to map the brain areas in which gray matter volume correlated with accurate reading of exception and pseudo-words.The results showed a differential pattern of exception and pseudo-word reading abilities in different clinical variants of PPA. Patients with semantic dementia, a disorder characterized by selective loss of semantic memory, revealed a pattern of surface dyslexia, while patients with logopenic/ phonological progressive aphasia, defined by phonological loop deficits, showed phonological dyslexia. Neuroimaging results showed that exception word reading accuracy correlated with gray matter volume in the left anterior temporal structures, including the temporal pole, the anterior superior and middle temporal and fusiform gyri, while pseudo-word reading accuracy correlated with left temporoparietal regions, including the posterior superior and middle temporal and fusiform gyri, and the inferior parietal lobule.These results suggest that exception and pseudo-word reading not only rely upon different language mechanisms selectively damaged in PPA, but also that these processes are sustained by separate brain structures.

Reading the reading brain: A new meta-analysis of functional imaging data on reading

“…Additional support to our results on the pseudoword network comes from recent studies, such as the one by Brambati et al (2009), where a correlational analysis between pseudoword reading accuracy and grey matter volume was performed and found to be significant for the left inferior parietal lobule (angular gyrus), the posterior aspect of the middle and superior temporal gyri, and the posterior fusiform gyrus. In Levy et al (2008), pseudoword reading yielded greater activation in a left parietal region close to our pseudoword-specific cluster in the same region, and in the left occipito-temporal area, in agreement with our findings.…”

“…In Brambati, Ogar, Neuhaus, Miller, and Gorno-Tempini (2009) a VBM (voxel-based morphometry) analysis was performed on a group of 54 subjects, including both normal subjects and patients suffering from different forms of neurodegenerative disease. Correlations between grey matter volume and reading accuracy, with respect to exception words and pseudowords respectively, were computed.…”

Syndromes of nonfluent primary progressive aphasia

“…40 In the GRN (no AOS/agrammatism) group, reading of all word types was affected, suggesting a more severe dyslexia. Cognitive domains beyond language may provide further information; episodic memory impairment (on the relatively easy test used here) was a consistent feature only of the LPA (no AOS/no agrammatism) group.…”

Triangulation of the neurocomputational architecture underpinning reading aloud

“…This pattern is strongly associated with semantic dementia (SD), a disorder in which patients suffer from a progressive, selective deterioration in semantic knowledge (26). Both reading deficits and semantic deficits in this group have been linked to atrophy centered on the left anterior temporal lobe (22,27,28), suggesting that this area makes a critical contribution both to semantic knowledge and to the reading of exception words. However, although these studies provide persuasive evidence for the co-occurrence of semantic impairment and exception word reading deficits, they provide limited data regarding the exact neuroanatomical locus of such effects.…”