title: Neural correlates of syntactic processing in the nonfluent variant of primary progressive aphasia.
abstract: The left posterior inferior frontal cortex (IFC) is important for syntactic processing, and has been shown in many functional imaging studies to be differentially recruited for the processing of syntactically complex sentences relative to simpler ones. In the nonfluent variant of primary progressive aphasia (PPA), degeneration of the posterior IFC is associated with expressive and receptive agrammatism; however, the functional status of this region in nonfluent PPA is not well understood. Our objective was to determine whether the atrophic posterior IFC is differentially recruited for the processing of syntactically complex sentences in nonfluent PPA. Using structural and functional magnetic resonance imaging, we quantified tissue volumes and functional responses to a syntactic comprehension task in eight patients with nonfluent PPA, compared to healthy age-matched controls. In controls, the posterior IFC showed more activity for syntactically complex sentences than simpler ones, as expected. In nonfluent PPA patients, the posterior IFC was atrophic and, unlike controls, showed an equivalent level of functional activity for syntactically complex and simpler sentences. This abnormal pattern of functional activity was specific to the posterior IFC: the mid-superior temporal sulcus, another region modulated by syntactic complexity in controls, showed normal modulation by complexity in patients. A more anterior inferior frontal region was recruited by patients, but did not support successful syntactic processing. We conclude that in nonfluent PPA, the posterior IFC is not only structurally damaged, but also functionally abnormal, suggesting a critical role for this region in the breakdown of syntactic processing in this syndrome.
authors.affiliation: Memory and Aging Center, Department of Neurology, University of California, San Francisco, California 94143, USA. smwilson@u.arizona.edu
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Wilson
authors.forename: Nina F
authors.initials: NF
authors.lastname: Dronkers
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Ogar
authors.forename: Jung
authors.initials: J
authors.lastname: Jang
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Growdon
authors.forename: Federica
authors.initials: F
authors.lastname: Agosta
authors.forename: Maya L
authors.initials: ML
authors.lastname: Henry
authors.forename: Bruce L
authors.initials: BL
authors.lastname: Miller
authors.forename: Maria Luisa
authors.initials: ML
authors.lastname: Gorno-Tempini
mesh_terms: D000368:Aged; D001284:Atrophy / Q000473:pathology; D001931:Brain Mapping / Q000379:methods; D032882:Comprehension / Q000502:physiology*; D005260:Female; D005625:Frontal Lobe / Q000473:pathology* / Q000503:physiopathology*; D006801:Humans; D007802:Language; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D057178:Primary Progressive Nonfluent Aphasia / Q000503:physiopathology*; D013067:Speech Perception; D013702:Temporal Lobe / Q000502:physiology