Apraxia of speech in aphasia maps to lesions in the arcuate fasciculus
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1
Beth Israel Deaconess Medical Center, Harvard Medical School, United States
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2
Beth Israel Deaconess Medical Center, Harvard Medical School, Neurology, United States
Introduction: Lesion location has been used determine regions responsible for particular deficits in disorders associated with stroke. However, when lesion location and symptomology overlap, as in apraxia of speech (AOS) and aphasia, the extent to which each contributes to the overall communication impairment can be difficult to isolate (Dronkers, 1996; Hillis et al., 2004). AOS is an acquired impairment of the ability to plan the sensorimotor commands for normal speech movements (Duffy, 2013), while aphasia is an acquired disorder affecting the ability to use or understand language. To examine the impact of lesion site on symptoms of these disorders, we first estimated the prevalence of AOS in group of 42 patients with chronic aphasia, then performed voxel‐based lesion-symptom mapping (VLSM; Rorden et al., 2007) analyses to determine whether the location of brain lesions can predict symptoms of AOS. VLSM tests each voxel to determine whether individuals with lesions in a particular location are more likely to experience a particular deficit than those without injury at that location.
Methods: We used the Apraxia of Speech Rating Scale (ASRS; Strand et al. 2014) to code speech tasks (conversation, “how-to” task, picture descriptions, word/sentence repetition, diadochokinesis) for 42 individuals with chronic aphasia (mean 32.4 months post-stroke ± 27.9; see Table 1). The ASRS’s 16 items correspond to characteristic features of AOS; each is rated on a scale from 0 (“not present”) to 4 (“nearly always evident and marked in severity”). Overall ASRS scores > 8 indicate a diagnosis of AOS. Performance on the Boston Naming Test (BNT; Kaplan et al., 1983) was used for a second VLSM analysis to contrast anomia maps with the AOS maps, but not for AOS ratings.
For VLSM analyses, lesion masks were first drawn manually on T1-weighted images by an experienced investigator, blinded to the question of interest, and normalized using SPM8. Significant relationships between left-hemisphere lesioned voxel clusters and ASRS scores MRIcron’s (z-scores; Brunner-Munzel test) Non-Parametric Mapping (NPM) software was used (false discovery rate correction, p ≤ 0.01). A critical threshold of 23% was applied (i.e., only voxels involved in at least 10 cases were used).
Results: 10% of videos were coded by two investigators to establish ASRS scoring reliability. Two-way random-effects ICCs for absolute agreement on single measures yielded a between-judge ICC of 0.897 on overall ASRS score. 38 participants were identified as having AOS, none with dysarthria. VLSM analysis revealed a distinct white-matter cluster corresponding to the longitudinal portion of the left dorsal arcuate fasciculus (AF) significantly associated with overall ASRS score (Figure 1 – blue). This was distinct from the large voxel clusters associated with BNT performance (Figure 1 – red).
Conclusions. Our finding associates the expression of AOS in aphasia to damage of the AF (the dorsal auditory-motor stream), distinct from the cluster identified using the BNT. Results are consistent with the hypothesis that lesions of the dorsal stream, connecting Wernicke’s and Broca’s areas, interfere with the mapping of acoustics to articulation (Basilakos et al., 2015; Hickok et al., 2014; Whitewell et al., 2013).
References
Basilakos, A., et al. (2015) Patterns of poststroke brain damage that predict speech production errors in apraxia of speech and aphasia dissociate. Stroke 46. 1561-1566.
Dronkers, N. (1996) A new brain region for coordinating speech articulation. Nature 384, 159-161.
Duffy, J. (2013). Motor speech disorders: Substrates, differential diagnosis, and management. St. Louis, MO: Elsevier.
Hickok, G., et al. (2014) Partially overlapping sensorimotor networks underlie speech praxis and verbal short-term memory: evidence from apraxia of speech following acute stroke. Frontiers in Human Neuroscience 8, article 649.
Hillis, et al. (2004) Re-examining the brain regions crucial for orchestrating speech articulation. Brain 127, 1479-1487.
Kaplan, E., et al.. (1983) Boston Naming Test. Philadelphia: Lea & Febiger.
Rorden, C., et al. (2007) Improving lesion-symptom mapping. J. Cognitive Neuroscience 19:7, 1081-1088.
Strand, E., et al. (2014) The apraxia of speech rating scale: A tool for diagnosis and description of apraxia of speech. J. Communication Disorders 51, 43-50.
Whitwell, J., et al. (2013) Distinct regional anatomic and functional correlates of neurodegenerative apraxia of speech and aphasia: An MRI and FDG-PET study. Brain & Language 125, 245-252.
Keywords:
apraxia of speech,
Aphasia,
Arcuate Fasciculus,
lesion maps,
VSLM
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:
Chenausky
KV,
Paquette
S,
Norton
AC and
Schlaug
G
(2019). Apraxia of speech in aphasia maps to lesions in the arcuate fasciculus.
Conference Abstract:
Academy of Aphasia 56th Annual Meeting.
doi: 10.3389/conf.fnhum.2018.228.00088
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Received:
30 Apr 2018;
Published Online:
22 Jan 2019.
*
Correspondence:
Dr. Karen V Chenausky, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, United States, ace@alum.mit.edu