title: Modulation of frontal effective connectivity during speech.
abstract: Noninvasive neurostimulation methods such as transcranial direct current stimulation (tDCS) can elicit long-lasting, polarity-dependent changes in neocortical excitability. In a previous concurrent tDCS-fMRI study of overt picture naming, we reported significant behavioural and regionally specific neural facilitation effects in left inferior frontal cortex (IFC) with anodal tDCS applied to left frontal cortex (Holland et al., 2011). Although distributed connectivity effects of anodal tDCS have been modelled at rest, the mechanism by which 'on-line' tDCS may modulate neuronal connectivity during a task-state remains unclear. Here, we used Dynamic Causal Modelling (DCM) to determine: (i) how neural connectivity within the frontal speech network is modulated during anodal tDCS; and, (ii) how individual variability in behavioural response to anodal tDCS relates to changes in effective connectivity strength. Results showed that compared to sham, anodal tDCS elicited stronger feedback from inferior frontal sulcus (IFS) to ventral premotor (VPM) accompanied by weaker self-connections within VPM, consistent with processes of neuronal adaptation. During anodal tDCS individual variability in the feedforward connection strength from IFS to VPM positively correlated with the degree of facilitation in naming behaviour. These results provide an essential step towards understanding the mechanism of 'online' tDCS paired with a cognitive task. They also identify left IFS as a 'top-down' hub and driver for speech change.
authors.affiliation: Language and Communication Sciences, City University London, Northampton Square, London EC1R 0JD, UK.
authors.forename: Rachel
authors.initials: R
authors.lastname: Holland
authors.affiliation: Institute of Cognitive Neuroscience, University College London, 17 Queen Square, London WC1N 3AR, UK.
authors.forename: Alex P
authors.initials: AP
authors.lastname: Leff
authors.affiliation: Wellcome Trust Centre for Neuroimaging, University College London, 12 Queen Square, London WC1N 3BG, UK.
authors.forename: William D
authors.initials: WD
authors.lastname: Penny
authors.affiliation: Human Movement and Balance Unit, Institute of Neurology, 33 Queen Square, London WC1N 3BG, UK.
authors.forename: John C
authors.initials: JC
authors.lastname: Rothwell
authors.affiliation: Institute of Cognitive Neuroscience, University College London, 17 Queen Square, London WC1N 3AR, UK. Electronic address: j.crinion@ucl.ac.uk.
authors.forename: Jenny
authors.initials: J
authors.lastname: Crinion
mesh_terms: D000328:Adult; D000368:Aged; D001931:Brain Mapping / Q000379:methods; D005260:Female; D005625:Frontal Lobe / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D009415:Nerve Net / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D009473:Neuronal Plasticity / Q000502:physiology*; D013060:Speech / Q000502:physiology*; D065908:Transcranial Direct Current Stimulation / Q000379:methods*
keywords: DCM — Dynamic Causal Modelling; IFS — inferior frontal sulcus; Speech production; VPM — ventral premotor cortex; fMRI — functional magnetic resonance imaging; tDCS — transcranial direct current stimulation
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