Search Abstracts | Symposia | Slide Sessions | Poster Sessions
Theta-Burst Stimulation of right inferior frontal gyrus reshapes frontal interhemispheric dynamics during picture naming: implications for aphasia rehabilitation.
Poster Session C, Thursday, October 1, 10:45 am - 12:45 pm, Wangari Maathai
Ajay Halai1, JeYoung Jung2, Matt Lambon Ralph1; 1MRC Cognition and Brain Sciences Unit, University of Cambridge, UK, 2School of Psychology, University of Nottingham, Nottingham, UK
The role of the right hemisphere in language production and recovery following left hemisphere damage remains contested. In particular, whether right inferior frontal gyrus (rIFG) activity reflects adaptive compensation or maladaptive upregulation has direct implications for aphasia rehabilitation, yet the neurobiological basis of targeting this region with non-invasive brain stimulation (NIBS) remain insufficiently characterised, and no study has directly tested whether inhibitory or excitatory stimulation of rIFG produces the predicted changes in cortical dynamics within the language network alongside corresponding behavioural effects. Here, we used a within-subject, counterbalanced design combining offline theta burst stimulation (TBS) with functional MRI in healthy adults to causally probe the role of rIFG during picture naming. Across three sessions, participants received continuous TBS (cTBS; inhibitory), intermittent TBS (iTBS; excitatory), or sham stimulation (auditory/tactile control), followed by a speeded picture naming task (1000 ms window) during fMRI. We hypothesised that cTBS and iTBS would produce opposing behavioural and neural effects, reflecting modulation of rIFG excitability and downstream effects on the broader language network via interhemispheric connectivity with left IFG. Twenty-five healthy, right-handed native English speakers (mean age = 25.16 years) completed all sessions. Stimulation was delivered at 80% resting motor threshold to rIFG pars triangularis (MNI: [51, 30, 14]). 3T MRI data were acquired and preprocessed using fMRIPrep and tedana. Behavioural data were analysed using linear mixed-effects models and fMRI data were analysed using SPM12. Effective connectivity was assessed using dynamic causal modelling (DCM), examining how TBS over the right IFG altered interhemispheric language dynamics. Behavioural accuracy differed significantly across conditions. iTBS significantly improved naming relative to sham (t = 4.13, p = 0.0004) and cTBS (t = 3.38, p = 0.0025), whereas cTBS did not differ from sham. Mean accuracy was highest following iTBS (76.17%) compared with sham (70.63%) and cTBS (71.43%). fMRI analyses replicated a predominantly left-lateralised naming network. Relative to sham, cTBS was associated with increased activation in left IFG pars triangularis and bilateral sensorimotor regions, whereas iTBS elicited broader increases across bilateral IFG, temporal, subcortical, and limbic regions. No differences emerged between cTBS-iTBS or for sham > stimulation contrasts. DCM revealed robust bilateral facilitatory intrinsic coupling between IFGs in the sham session. Relative to sham, both cTBS and iTBS increased right-to-left intrinsic connectivity, with no differences between active protocols, while left-to-right intrinsic connectivity remained positive and unchanged. Bayesian model selection revealed a shift in task-dependent modulatory architecture following stimulation. Both cTBS and iTBS reduced left-to-right modulatory connectivity during naming, again without differences between protocols. Finally, driving input parameters confirmed significant direct stimulation effects on rIFG in both active conditions. Together, these findings challenge a simple transcallosal inhibition account, demonstrating instead intrinsic bilateral facilitatory interactions during naming. TBS of rIFG selectively alters interhemispheric dynamics by strengthening intrinsic right-to-left coupling while attenuating task-dependent left-to-right modulation, revealing stimulation-induced reconfiguration of frontal language network connectivity. These results provide a mechanistic basis for considering rIFG modulation in aphasia rehabilitation.
Topic Areas: Language Production, Disorders: Acquired