Slide Slam A4
Morpho-syntactic processing in Primary Progressive Aphasia and stroke-induced aphasia: comparison of ERP response patterns
Elena Barbieri1, Brianne Chiappetta1, Haiyan Wang1, Ashley Backus1, Marek-Marsel Mesulam2,3, Cynthia K. Thompson1,2,3; 1Aphasia and Neurolinguistics Research Laboratory, Northwestern University, Evanston, IL, 2Mesulam Center for Cognitive Neurology and Alzheimer's Disease, Northwestern University, Chicago, IL, 3Department of Neurology, Northwestern University, Chicago, IL
Introduction. People with the agrammatic variant of Primary Progressive Aphasia (PPA-G) and people with stroke-induced agrammatic aphasia (StrAph) both present with nonfluent speech and morpho-syntactic impairments in the presence of spared semantic processing . However, in PPA-G grammatical deficits gradually emerge over time due to neurodegenerative disease, but occur suddenly following a cerebrovascular lesion in StrAph. Only a few studies have directly compared language deficits in StrAph and PPA, and none have used on-line paradigms, which are more sensitive to detect language deficits . In the present study, we compared on-line processing of subject-verb agreement violations in PPA-G and StrAph using ERP. Methods. Sixteen healthy (ages: 35-78 years), 7 StrAph, (ages: 26-72 years) and 10 PPA-G (ages: 52-76 years) participants completed a sentence acceptability judgment task while EEG was recorded from 32 scalp electrodes. Both patient groups presented with language impairments consistent with agrammatism, with StrAph showing an overall more severe language profile, reduced fluency, and greater impairment on offline measures of sentence processing than PPA-G. Study materials included sentences containing either a morpho-syntactic (subject-verb agreement, n=50) or a semantic (n=50) violation, as well as correct sentences (n=100). For each condition, mean EEG amplitude in pre-selected time windows was entered as a dependent variable in mixed-effects regression analyses, with sentence type (correct, violation) and electrode region (posterior left/right/midline, anterior left/right/midline) as fixed effects and participant as a random effect. Results. Morpho-syntactic violations elicited a significant, posteriorly-centered P600 in the group of healthy adults. Compared to the healthy controls, StrAph showed a delayed P600 with an anterior shift, while PPA-G showed no response to morpho-syntactic violations. Semantic violations elicited a significant, centro-parietally distributed N400 in all three participant groups. Conclusions. Results indicate that morpho-syntactic violations trigger processes of re-analysis/repair in healthy participants. While PPA-G participants fail to detect such violations, StrAph show successful detection but delayed re-analysis processes. The anterior shift of the P600 in StrAph replicates the findings of a previous study in older adults . Although the relationship between ERP scalp distribution and underlying neural sources is extremely complex, this result suggests increased reliance on domain-general resources  supporting re-analysis processes. In PPA-G, recruitment of domain-general cognitive resources may be hindered due to the more widespread cognitive decline in this group (see ). Results also suggest that semantic processing is preserved in both patient groups, in line with previous studies . Notably, no anterior shift of the N400 was observed in the StrAph group, suggesting that the abnormal P600 topography in this group does not simply reflect lesion-related shifts. References.  Thompson, C. K., & Mack, J. E. (2014). Aphasiology, 28, 1018-1037.  Barbieri, E., et al. (2021). Neuropsychologia, 151, 107728.  Kemmer, L., et al. (2004). Psychophysiology, 41(3), 372–384.  Fabiani, M., et al. (1998). Psychophysiology, 35(6), 698-708.  Silveri, M. C., et al. (2019). Cognitive and Behavioral Neurology, 32(4), 225-235.  Hurley, R. S., et al. (2009). Journal of Neuroscience, 29(50), 15762-15769.