The neural basis of surface dyslexia in semantic dementia
- PMID: 19022856
- PMCID: PMC2638692
- DOI: 10.1093/brain/awn300
The neural basis of surface dyslexia in semantic dementia
Abstract
Semantic dementia (SD) is a neurodegenerative disease characterized by atrophy of anterior temporal regions and progressive loss of semantic memory. SD patients often present with surface dyslexia, a relatively selective impairment in reading low-frequency words with exceptional or atypical spelling-to-sound correspondences. Exception words are typically 'over-regularized' in SD and pronounced as they are spelled (e.g. 'sew' is pronounced as 'sue'). This suggests that in the absence of sufficient item-specific knowledge, exception words are read by relying mainly on subword processes for regular mapping of orthography to phonology. In this study, we investigated the functional anatomy of surface dyslexia in SD using functional magnetic resonance imaging (fMRI) and studied its relationship to structural damage with voxel-based morphometry (VBM). Five SD patients and nine healthy age-matched controls were scanned while they read regular words, exception words and pseudowords in an event-related design. Vocal responses were recorded and revealed that all patients were impaired in reading low-frequency exception words, and made frequent over-regularization errors. Consistent with prior studies, fMRI data revealed that both groups activated a similar basic network of bilateral occipital, motor and premotor regions for reading single words. VBM showed that these regions were not significantly atrophied in SD. In control subjects, a region in the left intraparietal sulcus was activated for reading pseudowords and low-frequency regular words but not exception words, suggesting a role for this area in subword mapping from orthographic to phonological representations. In SD patients only, this inferior parietal region, which was not atrophied, was also activated by reading low-frequency exception words, especially on trials where over-regularization errors occurred. These results suggest that the left intraparietal sulcus is involved in subword reading processes that are differentially recruited in SD when word-specific information is lost. This loss is likely related to degeneration of the anterior temporal lobe, which was severely atrophied in SD. Consistent with this, left mid-fusiform and superior temporal regions that showed reading-related activations in controls were not activated in SD. Taken together, these results suggest that the left inferior parietal region subserves subword orthographic-to-phonological processes that are recruited for exception word reading when retrieval of exceptional, item-specific word forms is impaired by degeneration of the anterior temporal lobe.
Figures
Similar articles
-
Reading disorders in primary progressive aphasia: a behavioral and neuroimaging study.Neuropsychologia. 2009 Jul;47(8-9):1893-900. doi: 10.1016/j.neuropsychologia.2009.02.033. Epub 2009 Mar 9. Neuropsychologia. 2009. PMID: 19428421 Free PMC article.
-
The role of the left anterior temporal lobe in exception word reading: reconciling patient and neuroimaging findings.Neuroimage. 2012 May 1;60(4):2000-7. doi: 10.1016/j.neuroimage.2012.02.009. Epub 2012 Feb 14. Neuroimage. 2012. PMID: 22361167
-
Taking the sublexical route: brain dynamics of reading in the semantic variant of primary progressive aphasia.Brain. 2020 Aug 1;143(8):2545-2560. doi: 10.1093/brain/awaa212. Brain. 2020. PMID: 32789455 Free PMC article.
-
Normal and pathological reading: converging data from lesion and imaging studies.Neuroimage. 2003 Nov;20 Suppl 1:S30-41. doi: 10.1016/j.neuroimage.2003.09.012. Neuroimage. 2003. PMID: 14597294 Review.
-
Structural abnormalities in the dyslexic brain: a meta-analysis of voxel-based morphometry studies.Hum Brain Mapp. 2013 Nov;34(11):3055-65. doi: 10.1002/hbm.22127. Epub 2012 Jun 19. Hum Brain Mapp. 2013. PMID: 22711189 Free PMC article. Review.
Cited by
-
Genetic Modifications of Developmental Dyslexia and Its Representation Using In Vivo, In Vitro Model.Glob Med Genet. 2024 Feb 27;11(1):76-85. doi: 10.1055/s-0044-1781456. eCollection 2024 Jan. Glob Med Genet. 2024. PMID: 38414980 Free PMC article. Review.
-
Distinct parallel activation and interaction between dorsal and ventral pathways during phonological and semantic processing: A cTBS-fMRI study.Hum Brain Mapp. 2024 Jan;45(1):e26569. doi: 10.1002/hbm.26569. Hum Brain Mapp. 2024. PMID: 38224540 Free PMC article.
-
Neural mechanisms of sentence production: a volumetric study of primary progressive aphasia.Cereb Cortex. 2024 Jan 14;34(1):bhad470. doi: 10.1093/cercor/bhad470. Cereb Cortex. 2024. PMID: 38100360
-
The development of the Cognitive Assessment for Tagalog Speakers (CATS): A culturally and linguistically tailored test battery for Filipino Americans.Alzheimers Dement (N Y). 2023 Sep 1;9(3):e12418. doi: 10.1002/trc2.12418. eCollection 2023 Jul-Sep. Alzheimers Dement (N Y). 2023. PMID: 37662963 Free PMC article.
-
Distinguishing Semantic Variant Primary Progressive Aphasia from Alzheimer's Disease.J Alzheimers Dis Rep. 2023 Mar 28;7(1):227-234. doi: 10.3233/ADR-230010. eCollection 2023. J Alzheimers Dis Rep. 2023. PMID: 37090957 Free PMC article.
References
-
- Ashburner J, Friston KJ. Voxel-based morphometry – the methods. Neuroimage. 2000;11:805–21. - PubMed
-
- Ashburner J, Friston KJ. Unified segmentation. Neuroimage. 2005;26:839–51. - PubMed
-
- Benjamini Y, Hochberg Y. Controlling the false discovery rate: a practical and powerful approach to multiple testing. J R Stat Soc Ser B. 1995;57:289–300.
-
- Binder JR, Mohr JP. The topography of callosal reading pathways. A case-control analysis. Brain. 1992;115(Pt 6):1807–26. - PubMed
-
- Binder JR, McKiernan KA, Parsons ME, Westbury CF, Possing ET, Kaufman JN, et al. Neural correlates of lexical access during visual word recognition. J Cogn Neurosci. 2003;15:372–93. - PubMed