Abstract
We tested the hypothesis that motor planning and programming of speech articulation and verbal short-term memory (vSTM) depend on partially overlapping networks of neural regions. We evaluated this proposal by testing 76 individuals with acute ischemic stroke for impairment in motor planning of speech articulation (apraxia of speech, AOS) and vSTM in the first day of stroke, before the opportunity for recovery or reorganization of structure-function relationships. We also evaluated areas of both infarct and low blood flow that might have contributed to AOS or impaired vSTM in each person. We found that AOS was associated with tissue dysfunction in motor-related areas (posterior primary motor cortex, pars opercularis; premotor cortex, insula) and sensory-related areas (primary somatosensory cortex, secondary somatosensory cortex, parietal operculum/auditory cortex); while impaired vSTM was associated with primarily motor-related areas (pars opercularis and pars triangularis, premotor cortex, and primary motor cortex). These results are consistent with the hypothesis, also supported by functional imaging data, that both speech praxis and vSTM rely on partially overlapping networks of brain regions.
Highlights
As effortless as it seems, articulation of speech requires orchestration of an incredibly complex motor system: rapid and fine-tuned timing of movements of the lips, tongue, jaw, soft palate, vocal folds, laryngeal muscles, and respiratory muscles
There were no significant differences by independent t-tests between those with and without apraxia of speech (AOS) in age (57.8 ± SD 14.2 vs. 58.0 ± 12.6; t = 0.05; p = 0.96) or stroke severity measured by National Institutes of Health Stroke Scale (NIHSS)
Without the CONCLUSIONS The present study suggests that speech praxis depends on sensorimotor networks underlying speech motor control, which are at least partially shared by verbal short-term memory (vSTM) tasks like digit span
Summary
As effortless as it seems, articulation of speech requires orchestration of an incredibly complex motor system: rapid and fine-tuned timing of movements of the lips, tongue, jaw, soft palate, vocal folds, laryngeal muscles, and respiratory muscles. Work on the neural basis of verbal short-term memory (vSTM), predominantly based on functional imaging methods, has identified some of the same regions including portions of Broca’s area, the anterior insula, and premotor cortex (Awh et al, 1996; Smith and Jonides, 1997; Chein et al, 2002; Hickok et al, 2003; Buchsbaum and D’Esposito, 2008; Chein and Fiez, 2010) As mentioned, this apparent overlap is not unexpected as aspects of motor speech (articulatory rehearsal) constitute an important component of vSTM (Baddeley, 1992). Previous work suggests that AOS is associated with a network of regions, rather than a single region, which partially overlaps with the network associated with vSTM deficits in the same patients (Awh et al, 1996; Smith and Jonides, 1997; Chein et al, 2002; Hickok et al, 2003, 2011; Buchsbaum and D’Esposito, 2008; Terband et al, 2009; Golfinopoulos et al, 2010; Chein and Fiez, 2010; Houde and Nagarajan, 2011; Hickok, 2012)
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