Poster A11, Thursday, August 16, 10:15 am – 12:00 pm, Room 2000AB
Adaptive paradigms for mapping phonological regions in individual participants
Melodie Yen1, Andrew T. DeMarco2, Stephen M. Wilson1;1Vanderbilt University Medical Center, 2Georgetown University
Phonological encoding depends on left-lateralized regions in the supramarginal gyrus and the ventral precentral gyrus. Localizing these phonological regions in individual participants is important in several research and clinical contexts. These applications include presurgical language mapping, studying functional reorganization in recovery from aphasia, and as functional localizers for ROI-based analyses. Existing language mapping paradigms do not consistently localize these phonological regions in individual participants. To address this challenge, we designed two tasks that load on speech sound knowledge: a rhyme judgment task and a syllable counting task. In the rhyme task, participants decided whether or not two pseudowords rhymed. In the syllables task, they decided whether or not two pseudowords had the same number of syllables. Critically, both tasks used an adaptive staircase design to ensure that each individual found each task similarly challenging. The baseline was an adaptive perceptual judgment task. The goal of this study was to assess the validity of the two paradigms, in terms of their ability to produce left-lateralized activations within the supramarginal gyrus and ventral precentral gyrus in neurologically normal individuals with presumptively normal language organization. Sixteen healthy participants were scanned with fMRI as they performed the rhyme judgment paradigm, the syllable counting paradigm, and an adaptive semantic matching paradigm we have described previously, which reliably activates inferior frontal and posterior temporal language regions. We included this semantic paradigm to investigate the extent to which the phonological paradigms could successfully identify regions specific to phonological encoding and not just language processing in general. We found that the rhyme and syllable paradigms both activated supramarginal and ventral precentral regions in the majority of participants (supramarginal: 13/16 for both; precentral: 14/16 for rhyme and 15/16 for syllables). In contrast, these regions were almost never activated by the semantic matching paradigm (never more than 3/16), suggesting that these activations are driven by phonological encoding and not by generic language processing. The extent of supramarginal and precentral activation was greater for both phonological paradigms than the semantic paradigm (all pairwise t-tests p < 0.0001), while the phonological paradigms did not differ from one another. These activations were strongly left-lateralized, suggesting they reflect linguistic rather than domain-general cognitive processes. The mean lateralization index in the supramarginal gyrus was greater for the rhyming task (LI = 0.99 ± 0.03) than the syllables task (LI = 0.71 ± 0.38, p = 0.02), while both paradigms showed similar lateralization in the precentral gyrus (rhyme: LI = 0.84 ± 0.24; syllables: LI = 0.74 ± 0.32; p = 0.18). Because of its greater ability to reveal lateralized parietal activation, we advocate using the rhyme paradigm in future applications. In sum, our findings show that the proposed adaptive rhyme judgment paradigm robustly identifies phonological encoding regions in individual participants. In conjunction with the semantic matching paradigm, it can be used to derive multifaceted individual language maps whereby regions are distinguished in terms of specific language domains, going beyond the concept of undifferentiated “eloquent cortex”.
Topic Area: Phonology and Phonological Working Memory