Dissociations between fluency and agrammatism in primary progressive aphasia

Background: Classical aphasiology, based on the study of stroke sequelae, fuses speech fluency and grammatical ability. Nonfluent (Broca's) aphasia often is accompanied by agrammatism; whereas in the fluent aphasias grammatical deficits are not typical. The assumption that a similar relationship exists in primary progressive aphasia (PPA) has led to the dichotomisation of this syndrome into fluent and nonfluent subtypes.Aims: This study compared elements of fluency and grammatical production in the narrative speech of individuals with PPA to determine if they can be dissociated from one another.Methods & Procedures: Speech samples from 37 individuals with PPA, clinically assigned to agrammatic (N = 11), logopaenic (N = 20), and semantic (N = 6) subtypes, and 13 cognitively healthy control participants telling the "Cinderella Story" were analysed for fluency-i.e., words per minute (WPM) and mean length of utterance in words (MLU-W)-and grammaticality, i.e., the proportion of grammatically correct sentences, open-to-closed-class word ratio, noun-to-verb ratio, and correct production of verb inflection, noun morphology, and verb argument structure. Between-group differences were analysed for each variable. Correlational analyses examined the relation between WPM and each grammatical variable, and an off-line measure of sentence production.Outcomes & Results: Agrammatic and logopaenic groups both had lower scores on the fluency measures and produced significantly fewer grammatical sentences than did semantic and control groups. However, only the agrammatic group evinced significantly impaired production of verb inflection and verb argument structure. In addition some semantic participants showed abnormal open-to-closed and noun-to-verb ratios in narrative speech. When the sample was divided on the basis of fluency, all the agrammatic participants fell in the nonfluent category. The logopaenic participants varied in fluency but those with low fluency showed variable performance on measures of grammaticality. Correlational analyses and scatter plots comparing fluency and each grammatical variable revealed dissociations within PPA participants, with some nonfluent participants showing normal grammatical skill.Conclusions: Grammatical production is a complex construct comprising correct usage of several language components, each of which can be selectively affected by disease. This study demonstrates that individuals with PPA show dissociations between fluency and grammatical production in narrative speech. Grammatical ability, and its relationship to fluency, varies from individual to individual, and from one variant of PPA to another, and can even be found in individuals with semantic PPA in whom a fluent aphasia is usually thought to accompany preserved ability to produce grammatical utterances.