Dissociations Between Fluency And Agrammatism In Primary Progressive Aphasia

Area of Science:

• Neurology
• Linguistics
• Psychology

Background:

• Classical aphasiology links speech fluency and grammar, often associating nonfluent aphasia with agrammatism.
• Primary progressive aphasia (PPA) is often dichotomized into fluent and nonfluent subtypes based on this assumption.
• This study investigates whether fluency and grammar can be dissociated in PPA.

Purpose of the Study:

• To compare elements of fluency and grammatical production in the narrative speech of individuals with PPA.
• To determine if fluency and grammatical ability can be dissociated in PPA subtypes.
• To analyze the relationship between fluency measures and grammatical variables in PPA.

Main Methods:

• Analyzed narrative speech samples from 37 individuals with PPA (agrammatic, logopenic, semantic subtypes) and 13 controls.
• Assessed fluency using words per minute (WPM) and mean length of utterance (MLU-W).
• Evaluated grammaticality through sentence correctness, word ratios, and specific linguistic features (verb inflection, noun morphology, verb argument structure).

Main Results:

• Agrammatic and logopenic groups showed reduced fluency and grammaticality compared to semantic and control groups.
• Only the agrammatic group had significantly impaired verb inflection and argument structure.
• Dissociations were observed: some nonfluent individuals had normal grammar, and logopenic individuals showed variable grammar performance.
• Some semantic PPA participants displayed atypical word ratios.

Conclusions:

• Grammatical production is complex and can be selectively impaired by disease.
• Individuals with PPA demonstrate dissociations between fluency and grammatical production in narrative speech.
• The relationship between grammar and fluency in PPA varies individually and by subtype, even in semantic PPA.