Clinical Manifestations

Semantic cognition requires both semantic representation (conceptual knowledge), and semantic control (the ability to shape and manipulate information for a particular context/task) (Lambon Ralph, Jefferies, Patterson, & Rogers, 2017). Prior investigations have contrasted the semantic representation loss in semantic dementia with semantic control deficits in post-stroke semantic aphasia (SA) (Jefferies & Lambon Ralph, 2006; Thompson et al., 2022). The logopenic variant of primary progressive aphasia (lvPPA) has neuroanatomical commonalities with SA, including damage centred on the left temporoparietal and inferior frontal regions, and neuropsychological commonalities including executive and language impairments. Accordingly, we investigated whether lvPPA impairs semantic control. We compared 12 individuals with lvPPA, 9 with typical amnestic Alzheimer's disease (AD), and 12 age-matched healthy controls on a battery of verbal and non-verbal semantic, language, memory and executive functioning tests. The lvPPA patients spanned multiple levels of performance across the different tests and showed the characteristic features of a semantic control deficit: (i) They showed impairments in tests that require greater semantic demand (e.g., semantic association knowledge test more than straightforward word-picture matching); (ii) only lvPPA patients showed strong correlations between semantic and executive tests; (iii) an effect of item familiarity was not found in lvPPA patients; and (iv) both lvPPA and AD patients benefited from phonemic cueing on the Boston Naming Test. LvPPA patients' performance on semantic tests is similar to that of previously reported SA, suggesting an impairment of semantic control. Imaging analysis is underway and will be available at the AAIC conference. References: Jefferies, E., & Lambon Ralph, M. A. (2006). Semantic impairment in stroke aphasia versus semantic dementia: a case-series comparison. Brain, 129(Pt 8), 2132-2147. https://doi.org/10.1093/brain/awl153 Lambon Ralph, M. A., Jefferies, E., Patterson, K., & Rogers, T. T. (2017). The neural and computational bases of semantic cognition. Nat Rev Neurosci, 18(1), 42-55. https://doi.org/10.1038/nrn.2016.150 Thompson, H. E., Noonan, K. A., Halai, A. D., Hoffman, P., Stampacchia, S., Hallam, G., . . . Jefferies, E. (2022). Damage to temporoparietal cortex is sufficient for impaired semantic control. Cortex, 156, 71-85. https://doi.org/10.1016/j.cortex.2022.05.022.