Presentation
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Phase synchronization during phonological short-term memory
Poster D40 in Poster Session D, Wednesday, October 25, 4:45 - 6:30 pm CEST, Espace Vieux-Port
This poster is part of the Sandbox Series.
Priyanka Shah-Basak1,2, Vahab Youssofzadeh3, Isabelle Banke1, Candida Ustine3, Katrina Erikson2, Brian Schmit4, Jeffrey R. Binder1; 1Language Imaging Lab, Department of Neurology, Medical College of Wisconsin, Milwaukee WI USA, 2Cognition and Brain Stimulation Lab, Department of Neurology, Medical College of Wisconsin, Milwaukee WI USA, 3MEG Program, Department of Neurology, Froedtert Hospital & Medical College of Wisconsin, Milwaukee, WI USA, 4Integrative Neural Engineering & Rehabilitation Lab, Marquette University, Milwaukee WI USA
Language relies on rapid and dynamic neural processes. Distinct cortical regions, distributed across the temporal, parietal, and frontal lobes, store linguistic (semantic phonological, orthographic) representations, subserve automatic and controlled retrieval and selection of information, and enable short-term verbal memory. A fundamental mechanism thought to subserve information transfer across a functional network such as the language network is neuronal oscillatory activity. Neural oscillations are ubiquitous in the brain and are shown to support local neuronal communication, and coordinated or synchronized oscillatory activity between regions is thought to enable interregional communication. One mode of communication is via synchronization of phases of oscillatory activity. Phase describes a relationship between two (or more) signals that share the same oscillatory frequency. Synchronization of phases from two brain regions is hypothesized to reflect a mechanism by which distant task-relevant regions integrate information across a functional network. For example, several studies show that phase synchronization in the theta/alpha band (5-10 Hz) between prefrontal and temporal regions critically supports visual working memory. But the role of phase synchronization across the language network underpinning specific language functions after stroke remains largely understudied. Our focus in the current study is on elucidating oscillatory connectivity that underlies phonological short-term memory (pSTM) in older healthy individuals and stroke survivors with aphasia (SWA) using magnetoencephalography (MEG). Our long-term goal is to apply this knowledge to treat pSTM impairments after stroke with targeted STM therapy paired with neuromodulatory treatments such as transcranial alternating current stimulation (tACS) that influence brain oscillatory connectivity. We have collected pilot MEG data from 7 older healthy volunteers (out of 20) and 9 SWA (out of 15), who have completed a pSTM paradigm during MEG involving a delayed match-to-sample task with spoken consonant-vowel strings and a TONES control task involving pitch discrimination. The pilot data are currently being analyzed to evaluate the oscillatory connectivity correlates of pSTM. Phase synchronization in the theta and alpha (4-12 Hz) bands is computed using weighted phase lag index with respect to temporoparietal (TP) regions, which include the posterior superior temporal gyrus, planum temporale and adjacent posterior supramarginal gyrus. These TP regions are implicated in phonological retrieval, and the maintenance of auditory-verbal stimuli in STM over extended delay periods. During pSTM, the phonological representations are thought to be maintained by constantly refreshing them via internal articulatory rehearsal processes. We expect that these rehearsal processes would be supported by phase synchronization between TP and posterior frontal and insular regions, including the pars opercularis and Rolandic operculum. We also plan to explore cross-frequency coupling between theta phase and gamma amplitude within TP regions as a potential mechanism supporting pSTM. The MEG experiments and analyses, as planned in the current study, will elucidate key nodes and frequencies of oscillatory connectivity associated with phonological STM functions in healthy individuals and SWA. The data will identify potential targets for tACS paired with STM therapies to exogenously augment connectivity across specific phonological subnetworks in future studies.
Topic Areas: Disorders: Acquired, Phonology