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Task demands modulate the reliance of verbal working memory on motor vs. auditory systems: A multivariate lesion-mapping study

Maryam Ghaleh1*, Elizabeth H. Lacey1, 2, Mackenzie Fama1, Zainab Anbari1, Andrew DeMarco1 and Peter E. Turkeltaub1, 2
  • 1 Medical Center, Georgetown University, United States
  • 2 MedStar National Rehabilitation Hospital, United States

Introduction Working memory (WM) plays an important role in language processing by temporarily storing and keeping information active for further processing (Gernsbacher & Kaschak, 2006). How information is maintained in WM is still a matter of debate. Verbal WM in Baddeley’s model (Baddeley, 2003; Baddeley & Hitch, 1974) consists of a phonological store and a rehearsal process that keeps the information active through subvocal speech. Prior lesion and imaging studies have suggested that simple maintenance of verbal information relies primarily on auditory/phonological regions in the temporal lobe (Buchsbaum, Olsen, Koch, & Berman, 2005; Leff et al., 2009). It remains unclear if subvocal rehearsal is only engaged for more demanding tasks and if auditory-phonological maintenance regions are still required under those circumstances. We used support-vector-regression lesion-symptom mapping (SVR-LSM) in left hemisphere stroke survivors to address these questions. Methods Participants included 71 native English speakers with left-hemisphere stroke at least 6 months prior to the study. Participants completed four working memory tasks: forward digit span, backward digit span, forward spatial span, and backward spatial span. SVR-LSM was first used to identify lesions associated with lower scores in 1a) forward digit span controlling for forward spatial span, and 1b) backward digit span controlling for backward spatial span. Spatial span was controlled in these analyses to remove the effects of domain-general WM functions and isolate maintenance of verbal information. Then, we examined 2a) forward digit span controlling for forward spatial span and backward digit span, and 2b) backward digit span controlling for backward spatial span and forward digit span. These contrasts separate the areas more important for each digit span task. We controlled for lesion volume in all analyses and controlled for multiple comparisons using a permutation-based cluster threshold. Results Analyses 1a and 1b identified distinct areas involved in each digit span task, with pre- and primary motor cortex only for backward digit span, and posterior superior temporal gyrus (STG) only for forward digit span. Both tasks relied on regions in the supramarginal gyrus, parietal operculum, and posterior insula. Even at a reduced threshold (uncorrected P<.05) the tasks differentially relied on extensive motor vs. auditory regions. Analyses 2a and 2b confirmed this difference in a direct contrast; backward digit span relied on pre-motor cortex and forward digit span relied on STG. Discussion Results suggest that different mechanisms are involved in maintenance of verbal information during forward and backward digit span tasks. We suggest that unmanipulated maintenance during forward digit span (lower WM demands) relies on auditory-phonological storage in the STG, consistent with prior imaging and lesion studies (Buchsbaum, Olsen, Koch, & Berman, 2005; Leff et al., 2009). Manipulation of the information for backward digit span (higher WM demands) relies on pre-motor cortex for the rehearsal process, which reduces the reliance on STG for maintenance. The transformation into articulatory representations, required for completion of both tasks, relies on a sensory-motor interface at the junction of the temporal and parietal lobes (Buchsbaum et al., 2005; Hickok, 2012; Hickok, Okada, & Serences, 2009; Rogalsky et al., 2015).

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References

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Keywords: Verbal Working Memory, rehearsal, lesion-symptom mapping, forward digit span, backward digit span, Task demands

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: Ghaleh M, Lacey EH, Fama M, Anbari Z, DeMarco A and Turkeltaub PE (2019). Task demands modulate the reliance of verbal working memory on motor vs. auditory systems: A multivariate lesion-mapping study. Conference Abstract: Academy of Aphasia 56th Annual Meeting. doi: 10.3389/conf.fnhum.2018.228.00056

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Received: 30 Apr 2018; Published Online: 22 Jan 2019.

* Correspondence: PhD. Maryam Ghaleh, Medical Center, Georgetown University, Washington D.C., United States, mg1477@georgetown.edu