Abstract 2994: Acute Ischemia in Broca's Area is Associated with Apraxia of Speech and Phonological Short-Term Memory Deficit

Abstract

Background: Apraxia of speech (AOS) is commonly thought of as a motor programming deficit, but could be due to impaired ability to maintain the sequence of phonemes (speech sounds) in short-term memory (STM) while articulating the word. We hypothesized that AOS and impaired digit span are associated with acute ischemia (infarct and/or hypoperfusion) of pars opercularis of Broca’s area (Brodmann's area 44), and that severity of AOS and digit span would be strongly correlated. Methods: We tested 87 patients on the first day of admission for left hemisphere acute ischemic stroke (mean age= 60.0±15.9; mean education 13.6±3.7 years) with Apraxia Battery for Adults-II and digit span tests and MRI, including Diffusion and Perfusion Weighted Imaging (DWI, PWI). We defined Apraxia of Speech (AOS) as 3 or 4 abnormal scores on the subtests of ABA-II: Words of Increasing Length A and B (which scores an increase in articulatory errors with increased word length for short and longer words/phrases, respectively), Repeated Trials (which scores variability in errors in repetition of the same polysyllabic words), and Inventory of Articulation (which scores characteristics of AOS). We defined impaired phonological STM as forward digit span < 5 or backward digit span < 3. The first author and 1 other technician, masked to the AOS results, examined MRI DWI and PWI scans for the presence or absence of ischemia (bright on DWI and/or hypoperfused on PWI) in each of 12 regions of interest: Brodmann’s area (BA) 4, 6, 10, 11, 19, 20, 21, 22, 37, 38, 39, 40, 44, 45, anterior and posterior insula. Hypoperfusion was defined as > 4 sec delay in TTP compared to opposite hemisphere. We evaluated association between the ischemia in each Brodmann area (BA) and (1) presence of AOS and (2) impaired STM using chi square tests. Results: AOS was significantly associated only with BA 6 (premotor cortex; chi square= 7.07; df1; p<.003) and BA 44 (pars opercularis of Broca’s area; chi square= 5.3; df1; p<.02), but not BA 45 (pars triangularis) or other ROIs. Impaired STM measured by forward digit span <5 was associated with BA 6 (chi square= 20.2; df1; p<.000001) and BA 44 (chi square= 15.2; df1; p=.00009), and BA 45 (chi square= 19.2; df1; p=.0001). There was strong correlation between digits forward span and Repeated Trials score (r=.35; p=.003), either because both speech articulation and STM rely on Broca’s area, or because orchestration of speech articulation demands holding phoneme sequences in phonological STM. Conclusions: Acute ischemia of the pars opercularis of Broca’s area (Brodmann’s Area 44) is associated with AOS and STM deficits. The severity of AOS and digit span deficits were highly correlated. The relationship between AOS and phonological STM begs further investigation.