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Poster D71, Thursday, November 9, 6:15 – 7:30 pm, Harborview and Loch Raven Ballrooms

The Neural Basis of Phonological and Orthographic Working Memory: Implications for Working Memory Models

Brenda Rapp1, Jeremy Purcell1, Randi Martin2;1Johns Hopkins University, 2Rice University

Neuroimaging and neuropsychological evidence suggests that the left parietal lobe supports working memory for phonological representations derived from speech perception (e.g., Vallar & Papagno, 1995; Martin, Wu, Jackson, Freedman, & Lesch, 2003; Yue, Dial, & Martin, 2016) and working memory for orthographic representations involved in spelling (Rapp, Purcell, Hillis, Capasso, & Miceli, 2016; Rapp & Dufor, 2011). Given that dissociations between orthographic working memory (OWM) and phonological working memory (PWM) have been reported (Rapp, Shea, Mis & Martin, 2016), some distinct brain regions are presumably involved. Historically, it has been assumed that the inferior parietal lobe serves as the neural basis of a storage buffer specific to PWM (Warrington, Logue, & Pratt, 1971; Vallar & Papagno, 1995). However, it is possible that the same parietal region is involved for the two domains because it carries out some general function, such as in directing attention to representations maintained elsewhere. Shared parietal substrates for phonological and orthographic WM would be consistent with embedded processes models of WM, which assume that WM consists of the activated portion of LTM, with frontal-parietal regions involved in bringing these representations in to the focus of attention (Cowan, Li, Moffitt et al., 2011). The present study, which examined lesion localization for individuals with selective PWM or OWM, is the first to directly address whether the same or distinct parietal regions are involved in WM in the two domains. Methods: Nine individuals with left-hemisphere strokes were separated into an OWM deficit group and a PWM deficit group. The OWM deficit group (5 individuals; 3 females) had well-documented OWM deficits in spelling, without deficits in LTM for orthography or in PWM in speech perception. The PWM deficit group (4 individuals; 0 female) had well-documented PWM deficits for speech, without deficits in LTM for phonology or in OWM in spelling. The neuroimaging modalities included 1 CT scan and 8 T1-weighted MRI scans. MRIcron was used to draw and overlay each lesion. Enantiomorphic normalization was carried out via SPM12; this approach derives non-linear normalization parameters from intact tissue in the undamaged homologous region of the intact contralesional hemisphere (Nachev, Coulthard, Jäger, Kennard, & Husain, 2008). Normalized lesion maps were overlaid on a template brain; coordinates are reported in MNI space. Results and conclusions. The results of the lesion overlays revealed non-overlapping brain regions for the two groups in the parietal lobe and elsewhere. The parietal region for the PWM group was in the supramarginal gyrus while the region for OWM group was more posterior and superior. These parietal regions showed good convergence with regions activated in fMRI studies of OWM (-28, -54, 57; Rapp & Dufour, 2011) and PWM (-55, -36, 23; Wu et al., 2003; Yue et al., 2016) for neurotypical individuals, showing domain-specific topography. Thus, the results appear more consistent with these parietal regions supporting domain-specific WM processes rather than a unitary attentional function predicted by embedded process accounts of WM.

Topic Area: Phonology and Phonological Working Memory

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