Exploring the impact of laterality and polarity of tDCS on therapy for chronic post-stroke anomia

Abstract

Event Abstract Back to Event Exploring the impact of laterality and polarity of tDCS on therapy for chronic post-stroke anomia Margaret Sandars1*, Lauren L. Cloutman1 and Anna M. Woollams1 1 University of Manchester, School of Psychological Sciences, United Kingdom Introduction: Anomia is a frequent and persistent symptom of post-stroke aphasia. Transcranial Direct Current Stimulation (tDCS) is a non-invasive neurostimulation technique that can be used to enhance the effects of behavioural speech and language therapy. Previous studies have suggested that applying anodal (excitatory) tDCS to perilesional areas in the damaged left hemisphere and/or cathodal (inhibitory) tDCS to homologous areas in the intact right hemisphere may be particularly beneficial (e.g. Baker et al., 2010; Rosso et al., 2014). However, the effects of varying both polarity and laterality of tDCS have yet to be systematically investigated within participants. The aim of the current study was to determine the optimal tDCS parameters to increase naming ability in two stroke survivors with chronic anomia: JSc, with Broca’s aphasia, and JSo, with Anomic aphasia. Methods: Six individualised 20-item treated sets were created from a pool of those incorrectly named prior to therapy. Participants completed six therapy cycles, each involving a different stimulation condition: left perilesional anodal, cathodal and sham and right contralesional anodal, cathodal and sham. Perilesional sites were determined on the basis of MRI structural scans: JSc=inferior frontal gryus (IFG), JSo=posterior superior temporal gyrus (STG). In each cycle, participants received 20 minutes of 1mA tDCS (electrodes 5cm x 7cm) on three consecutive days alongside computerised naming therapy. In the sham conditions, anodal stimulation was applied for one minute before being slowly turned off. Results: For JSc, there were significant immediate gains following left anodal, left cathodal and right sham stimulation, one week after left cathodal stimulation, and three weeks after left anodal and left cathodal stimulation. The effect of left anodal stimulation was significantly greater than that for sham immediately post-therapy (χ2=4.57, p<0.05), and three weeks later (χ2=6.99, p<0.01). JSo named significantly more items correctly immediately in all conditions, one week after left cathodal, right anodal, right cathodal and right sham stimulation, and three weeks after left cathodal, right cathodal and right sham stimulation. None of the active stimulation conditions resulted in significantly greater item gains than sham. Conclusion: Although there were clear therapeutic gains across the majority of conditions for both patients, the additional benefits for neurostimulation were more selective. For JSc, the beneficial effect of behavioural therapy for anomia was enhanced by anodal tDCS applied to left frontal perilesional regions, consistent with Baker et al. (2010) and Vestito et al. (2014), and neuroimaging of recovery and therapeutic gains in patients with chronic anomia (e.g. Fridriksson, 2010; Fridriksson et al., 2012; Meinzer et al., 2008). There was no benefit associated with cathodal stimulation of right contralesional sites, inconsistent with Rosso et al. (2014). In contrast, active tDCS did not increase JSo’s therapy gains above those observed for sham, irrespective of laterality and polarity. Overall, our results highlight variability of chronic stroke aphasic patients with differing behavioural and lesion profiles in their response to tDCS. Figure 1 Acknowledgements This research was funded by a Stroke Association Junior Research Training Fellowship awarded to the lead author (Award number TSA JRTF 2013/01) References