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Non-perceptual regions in the left supramarginal gyrus support phonological short-term memory: evidence from lesion-symptom mapping and fMRI studies

Qiuhai Yue1, Heather Dial1 and Randi Martin1*
  • 1 Rice University, Department of Psychology, United States

Phonological short-term memory (pSTM) refers to the capacity for retaining speech sounds for short periods of time. The current study evaluated two theories of pSTM: the buffer account, which proposes a dedicated pSTM store (Baddeley, Lewis, & Vallar, 1984; Martin, Lesch, & Bartha, 1999), and the embedded processes account, which argues that pSTM consists of the activated portion of phonological long-term memory (Cowan, 2001). Early evidence supporting the buffer account came from neuropsychological studies finding that speech perception abilities dissociate from pSTM capacity (Martin & Breedin, 1992; Warrington & Shallice, 1969) and the brain regions involved in speech perception and pSTM differ (superior temporal gyrus , STG, for perception; inferior parietal for pSTM; Shallice & Vallar, 1990; Warrington, Logue, & Pratt, 1971). However, recent patient studies appear to support the embedded processes account, with lesion-symptom mapping analyses suggesting that auditory STM and speech processing share the same neural substrate (left STG; Leff et al., 2009). Further, a recent neuroimaging study on healthy subjects reported sustained activity in posterior STG, not in inferior parietal regions (Ravizza, Hazeltine, Ruiz, & Zhu, 2011). However, Leff et al. partialled out non-word repetition in the pSTM analysis, which is problematic because non-word repetition has been assumed to tap pSTM abilities (Gathercole & Baddeley, 1989), while Ravizza et al. (2011) assumed a speech processing region posterior to that typically identified, making it unclear whether the maintenance region was actually a speech processing region. The present study addressed the limitations of previous studies, obtaining evidence from lesion-symptom mapping and neuroimaging approaches. Data from 19 left hemisphere brain damaged patients with mild to moderate language deficits were used in a lesion-symptom mapping analysis. Lesions were traced onto each patient’s T1 scan in native space and then the images were converted to standard space. Percent damage was calculated in 19 ROIs (from AAL template) and correlated with pSTM (composite: digit and digit matching span). Analyses controlled for speech perception (composite: consonant discrimination, auditory lexical decision, word-picture matching) and overall lesion size. After correcting for multiple comparisons, only the left supramarginal and angular gyri were significantly correlated with pSTM (Figure 1A). In an fMRI study, we scanned 15 healthy young adults while they performed an immediate discrimination task (speech perception) and a delayed recognition task (pSTM). In both, we manipulated the stimulus type (nonwords vs. chords), and for pSTM we manipulated memory load (one vs. three-items). Analyses revealed activation in left STG related to the speech perception task but, contrary to the predictions of the embedded processes approach, neither sustained activation (relative to the fixation baseline) nor a memory load effect during the maintenance period of the pSTM task (Figure 1B). In contrast, consistent with the buffer approach, a load effect was observed during the pSTM task in dorsal parieto-frontal regions, including the supramarginal gyrus (Figure 1C). Taken together, these data provide converging evidence supporting a buffer account of pSTM in which non-perceptual regions in the left inferior parietal lobe serve as a buffer for maintaining phonological representations.

Figure 1
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References

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Keywords: phonological short-term memory, buffer, supramarginal gyrus, lesion-symptom mapping, fMRI

Conference: 54th Annual Academy of Aphasia Meeting, Llandudno, United Kingdom, 16 Oct - 18 Oct, 2016.

Presentation Type: Poster Sessions

Topic: Student Submissions

Citation: Yue Q, Dial H and Martin R (2016). Non-perceptual regions in the left supramarginal gyrus support phonological short-term memory: evidence from lesion-symptom mapping and fMRI studies. Front. Psychol. Conference Abstract: 54th Annual Academy of Aphasia Meeting. doi: 10.3389/conf.fpsyg.2016.68.00045

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Received: 26 Apr 2016; Published Online: 15 Aug 2016.

* Correspondence: Prof. Randi Martin, Rice University, Department of Psychology, Houston, Texas, United States, rmartin@rice.edu