Plasticity of sentence processing networks: evidence from a patient with agrammatic variant of primary progressive aphasia (PPA)

ABSTRACT

This study reports the results of a longitudinal study examining the effects of treatment for sentence processing deficits for a 70-year-old gentleman (DK) with the agrammatic variant of Primary Progressive Aphasia (PPA). On entry into the study, he presented with a 2-year history of impaired verb and sentence processing and concomitant neural atrophy in primarily subcortical regions. Spanning an 18-month period, treatment focused on improving comprehension and production of syntactically complex, passive and object cleft, structures, consecutively. Results, derived from extensive behavioral and neurocognitive testing, showed not only improved ability to comprehend and produce both trained and untrained, less complex, linguistically related structures in offline tasks, but also improved online sentence processing strategies as revealed by partially normalized eye movements in online comprehension (i.e., emergence of thematic prediction and thematic integration) and production (i.e., use of incremental processing) tasks. Changes in neural activation from pre- to post-treatment of both structures also were found, with upregulation of tissue in both the left and right hemispheres, overlapping with regions recruited by neurotypical adults performing the same task. These findings indicate that Treatment of Underlying Forms (TUF) is effective for treatment of patients with the agrammatic variant of PPA (as it is for those with stroke-induced agrammatism), and show that unaffected neural tissue in patients with PPA is malleable and may be recruited to support language, providing evidence of experience-based plasticity in neurodegenerative disease.

KEYWORDS:

• Neural plasticity
• Primary Progressive Aphasia (PPA)
• agrammatic variant of PPA
• treatment of Underlying Forms (TUF)
• WH-movement structures
• NP-movement structures
• eyetracking
• visual world paradigms
• functional neuroimaging

Acknowledgments

This study was supported by the National Institutes of Health under Grants R01-DC01948 and P50-DC012283, awarded to Cynthia K. Thompson, and Grant R01-DC008552, awarded to Marek-Marsel Mesulam. We are grateful to Dr. Kaitlyn Litcofsky for her contributions to the development and the analysis of the eye-tracking experiments, and to Brianne Chiappetta, Hannah Guion and Kristie Brockway for assistance with language training.

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Institutes of Health [P50DC012283, R01-DC008552, R01DC01948].