Poster B13, Tuesday, August 20, 2019, 3:15 – 5:00 pm, Restaurant Hall
The neural process of becoming a word as revealed by triple-echo fMRI
Katherine Gore1, Ajay Halai2, Anna Woollams1, Matt Lambon Ralph2;1University of Manchester, 2University of Cambridge
Neuroimaging studies of language rehabilitation-induced neural changes in post-stroke aphasia have yielded inconsistent results. These heterogenous results are difficult to interpret, as there is no ‘typical’ baseline of neural change in response to speech and language therapy (SLT) based learning in normal controls for comparison. This study sought to provide this information by conducting computer-based language training with semantic and phonological cues. Critically, newly learned items were compared to both previously unknown and also unknown/untrained items, providing a continuum of lexicalisation. Participants learned name-picture pairs of previously unknown, low word frequency nouns and item descriptions over three weeks. Training was successful with a mean 91% gain, with an average 4.12 hours training. Imaging data were acquired post-therapy with a triple-echo planar imaging paradigm. There were four blocked conditions: previously known items (100% accuracy pre-training), newly trained items (100% accuracy post-training), unknown and untrained (0% accuracy pre- and post-training) and a baseline of phase-scrambled images. Items were specific per participant and participants responded out-loud to all trials. Images were pre-processed including ME-ICA (Kundu et al., 2017) in FSL and AFNI, and analysed using the general linear model in SPM. In an a priori region of interest (ROI) analysis, spherical ROIs with an 8-mm radius were defined from peak co-ordinates in a meta-analysis of fMRI episodic memory tasks (bilateral hippocampi) and semantic/language tasks (left inferior frontal gyrus (IFG), angular gyrus (AG), bilateral anterior temporal lobes (ATLs). For the known>unknown contrast, there was a significant positive correlation between in-scanner normalised, median reaction times (RT) for known items and activation in the left IFG, AG and bilateral ATLs. There was no significant correlation for the hippocampi. Conversely, for the trained>unknown contrast, the results are reversed. There was a significant negative correlation between trained item RT and activation in the IFG, AG and ATLs, but a significant positive correlation between trained item RT and hippocampal activation. All correlations were significantly different between conditions within ROI. All significant differences are reported at p < .05. Consistent with the complementary learning systems (CLS; McClelland, McNaughton, & O’Reilly, 1995) model, these results indicate that 1) for established vocabulary (known items), less neural effort is required for more quickly accessible lexical items, but with no CLS type component, 2) retrieval of newly-learned items is initially supported by regions associated with episodic memory and 3) consolidation of learning (and resultant decreased RT) leads to learned-word retrieval being supported by regions associated with language/semantic memory, less so by the episodic memory regions. When these results are compared with the same paradigm in people with aphasia, we can explore to what extent therapy-induced changes parallel to those seen in novel vocabulary acquisition in the healthy brain. These results have implications for optimising future word-finding therapies and improving treatment outcomes for patients with aphasia.
Themes: Language Therapy, Language Production
Method: Functional Imaging