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Poster D73, Thursday, November 9, 6:15 – 7:30 pm, Harborview and Loch Raven Ballrooms

Modulating the left inferior frontal cortex by task, task challenge and tDCS

Davide Nardo1, Katerina Pappa1, John Duncan2, Peter Zeidman3, Martina Callaghan3, Alexander Leff1,3,4, Jennifer Crinion1;1Institute of Cognitive Neuroscience, University College London, London, UK, 2MRC Cognition and Brain Sciences Unit, University of Cambridge, Cambridge, UK, 3Wellcome Trust Centre for Neuroimaging, University College London, London, UK, 4Department of Brain Repair and Rehabilitation, Institute of Neurology, University College London, London, UK

Background. The left inferior frontal cortex (LIFC) is a key region in spoken language processing. Indeed, previous studies from our lab have shown that anodal transcranial direct current stimulation (tDCS) delivered to the LIFC enhances spoken naming reaction times (RTs) more than sham tDCS [Holland et al., Curr Biol 2011], and modulates effective connectivity between the LIFC and premotor cortex during naming [Holland et al., Neuroimage 2016]. A matter of more recent debate is whether the LIFC’s role is domain-specific (i.e., linguistic), or domain-general (i.e., involved in multiple challenging cognitive functions) [Fedorenko & Thompson-Schill, Trends Cogn Sci 2014]. In this study we directly addressed how the LIFC is modulated by different tasks and task challenges in a concurrent tDCS/fMRI experiment. Method. 17 healthy right-handed English native speakers underwent an fMRI study in a 2 x 2 x 2 x 2 (Task x Challenge x Modality x tDCS) factorial design. Subjects were asked to perform both a linguistic (picture naming) and a non-linguistic (size judgment) task in two sessions one week apart. Stimuli were 480 pictures of monosyllabic objects. Task challenge (low vs. high ambiguity) was manipulated by varying: i) visually, the amount of noise overlapping the picture (5 vs. 15 squiggly lines); ii) aurally, the cue delivered concurrently with the picture (initial phoneme vs. noise). All subjects received both tDCS conditions (either anodal or sham on each session) delivered to the LIFC, with the order counterbalanced across subjects. Overt spoken responses (object names, yes/no replies for size judgement) were recorded online, and RTs were computed. Results. RTs data showed a significant main effect of Challenge (p<.001) for both visual and auditory modality (i.e., higher ambiguity resulted in slower RTs), no significant main effect of Task (i.e., tasks were behaviourally matched overall), and no significant main effect of tDCS. Significant tDCS x Challenge (p=.027) and tDCS x Task x Challenge (p<.005) interactions were found for the visual modality with anodal tDCS facilitating on-line performance. fMRI data (p<.05 FWE-corrected) showed that both tasks engaged a common bilateral network including the LIFC, supplementary motor area, visual, auditory and premotor cortices. In contrast to the behavioural data, there was a main effect of Task with the LIFC significantly activated more in the naming than in the judgment task. Mirroring our RTs results, there was a main effect of Challenge revealed in visual and auditory sensory cortices, and no significant main effect of tDCS. Furthermore, the tDCS x Challenge and tDCS x Task x Challenge interactions in the visual modality were replicated, with left premotor cortex and LIFC respectively showing neuro-modulatory effects of anodal tDCS (p<.001-uncorrected). Conclusion. Our data suggest that the LIFC is domain-general (i.e., involved in both cognitive tasks), yet activated more during naming, even though behavioural performance was matched across tasks. Both behaviourally and neurally there were complex interactions between task, task challenge, and tDCS. Anodal tDCS facilitated on-line performance (faster RTs), and modulated BOLD activity of the task-engaged frontal cortices in the vicinity of the stimulating electrode.

Topic Area: Control, Selection, and Executive Processes

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