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Beyond the cortex: A look at unique contributions of the arcuate fasciculus to language processing

Maria Ivanova1, 2*, Allison Zhong1, And Turken1, Brian Curran1 and Nina F. Dronkers1, 3, 4
  • 1 VA Northern California Health Care System, Center for Aphasia and Related Disorders, United States
  • 2 National Research University Higher School of Economics, Center for Brain and Language, Russia
  • 3 University of California, Berkeley, United States
  • 4 University of California, Davis, United States

Current evidence strongly suggests that the arcuate fasciculus (AF) is critical for language: from spontaneous speech and word retrieval to repetition and comprehension abilities (Breier et al., 2008; Hope et al., 2016; Ivanova et al., 2016; Kümmerer et al., 2013; Marchina et al., 2011; Wilson et al., 2011). However, to further pinpoint its role in language, its differential and unique contribution to language processing beyond that contributed by known cortical language areas must be established. We address this in a comprehensive evaluation of the specific functional role of the AF in a large cohort of individuals with chronic aphasia. Language abilities in patients with aphasia (n=33) following left hemisphere stroke were tested with the Western Aphasia Battery-Revised (Kertesz, 2007). Diffusion-weighted MR imaging was done on a 3T scanner (64 directions, 2 mm isovoxel, b = 2000 s/mm2, 10 b0 volumes). Tractography based on the spherical deconvolution model was performed using StarTrack. The AF in the left and right hemispheres were then manually reconstructed using a modified 3-segment model (Catani, Jones, & ffytche, 2005; see Figure 1), with a long segment dorsally connecting frontal areas with temporal, and two short segments that connect frontal or temporal areas to inferior parietal cortex. For tract metrics, normalized volume and Hindrance Modulated Orientation Anisotropy (index of tract integrity) were used. Damage to other brain areas was indexed based on lesion load to: i) specific cortical language areas – inferior frontal and posterior temporal – taken from the Harvard-Oxford Cortical Structural Atlas; ii) areas identified as significant in a VLSM analyses; iii) anterior and posterior bottleneck regions, isolated at the intersection of several white matter pathways (Griffis et al., 2017) (see Figure 1). Specific contributions of AF segments to language while accounting for the role of these areas was tested using multiple regression analyses. Involvement of the following tract segments in language processing beyond the contribution of cortical areas was demonstrated: the long segment of the AF contributed to overall language impairment (WAB AQ) and repetition abilities; anterior segment – to fluency and naming; the posterior segment – to comprehension. Once damage to areas identified in VLSM analyses was taken into account, no residual contribution of tract segments could be detected, except for the contribution of the anterior segment to repetition. Similarly, no significant role of tract segments beyond damage to bottleneck regions could be found, except for the involvement of the anterior segment in fluency. Individual cases of patients with total resection of the long segment of the AF and greatly varying language performance will also be discussed. For the first time, the contribution of the AF to language processing is comprehensively investigated while damage to cortical regions is systematically taken into account. First, the results highlight the important contributions of fiber pathways to language impairments beyond that of known cortical language areas. Second, results demonstrate that VLSM analysis can properly identify critical damage to white matter pathways. Third, the findings reinforce the vital role of the white bottleneck regions in sustaining language abilities.

Figure 1
Image

References

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Keywords: Aphasia, Language, Arcuate Fasciculus, fiber pathways, Bottleneck

Conference: Academy of Aphasia 56th Annual Meeting, Montreal, Canada, 21 Oct - 23 Oct, 2018.

Presentation Type: poster presentation

Topic: not eligible for a student prize

Citation: Ivanova M, Zhong A, Turken A, Curran B and Dronkers NF (2019). Beyond the cortex: A look at unique contributions of the arcuate fasciculus to language processing. Conference Abstract: Academy of Aphasia 56th Annual Meeting. doi: 10.3389/conf.fnhum.2018.228.00087

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Received: 01 May 2018; Published Online: 22 Jan 2019.

* Correspondence: Dr. Maria Ivanova, VA Northern California Health Care System, Center for Aphasia and Related Disorders, Mather, California, United States, ivanova@berkeley.edu