A novel frontal pathway underlies verbal fluency in primary progressive aphasia
Brain. 2013-07-02; 136(8): 2619-2628
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1. Brain. 2013 Aug;136(Pt 8):2619-28. doi: 10.1093/brain/awt163. Epub 2013 Jul 2.
A novel frontal pathway underlies verbal fluency in primary progressive aphasia.
Catani M(1), Mesulam MM, Jakobsen E, Malik F, Martersteck A, Wieneke C, Thompson
CK, Thiebaut de Schotten M, Dell’Acqua F, Weintraub S, Rogalski E.
(1)Natbrainlab, Department of Forensic and Neurodevelopmental Sciences, Institute
of Psychiatry, King’s College London, London, UK.
The frontal aslant tract is a direct pathway connecting Broca’s region with the
anterior cingulate and pre-supplementary motor area. This tract is left
lateralized in right-handed subjects, suggesting a possible role in language.
However, there are no previous studies that have reported an involvement of this
tract in language disorders. In this study we used diffusion tractography to
define the anatomy of the frontal aslant tract in relation to verbal fluency and
grammar impairment in primary progressive aphasia. Thirty-five patients with
primary progressive aphasia and 29 control subjects were recruited. Tractography
was used to obtain indirect indices of microstructural organization of the
frontal aslant tract. In addition, tractography analysis of the uncinate
fasciculus, a tract associated with semantic processing deficits, was performed.
Damage to the frontal aslant tract correlated with performance in verbal fluency
as assessed by the Cinderella story test. Conversely, damage to the uncinate
fasciculus correlated with deficits in semantic processing as assessed by the
Peabody Picture Vocabulary Test. Neither tract correlated with grammatical or
repetition deficits. Significant group differences were found in the frontal
aslant tract of patients with the non-fluent/agrammatic variant and in the
uncinate fasciculus of patients with the semantic variant. These findings
indicate that degeneration of the frontal aslant tract underlies verbal fluency
deficits in primary progressive aphasia and further confirm the role of the
uncinate fasciculus in semantic processing. The lack of correlation between
damage to the frontal aslant tract and grammar deficits suggests that verbal
fluency and grammar processing rely on distinct anatomical networks.
PMID: 23820597 [Indexed for MEDLINE]