Poster C54, Wednesday, August 21, 2019, 10:45 am – 12:30 pm, Restaurant Hall
Modulating verbal fluency performance in healthy adults with transcranial direct current stimulation over the left prefrontal cortex
Jana Klaus1, Gesa Hartwigsen1;1Lise Meitner Research Group Cognition and Plasticity, Max Planck Institute for Human Cognitive and Brain Sciences
Previous studies in healthy populations have provided equivocal evidence as to whether the application of transcranial direct current stimulation (tDCS) over the left prefrontal cortex can improve performance in verbal fluency tasks, with some reporting increased fluency rates following anodal compared to sham stimulation and others finding no effect. Critically, some methodological aspects may have confounded efficacy. First, previous studies have used sample sizes which were too low to reliably detect the small effect sizes associated with behavioural changes induced by tDCS. Second, the electrode montage used in previous studies may not have been successful in effectively targeting the left prefrontal cortex. Simulation studies have shown that the strongest electric field is in fact evoked between the electrodes, and not under the “active” electrode, which is routinely placed over the cortical area of interest. Third, typically no task relevant to the studied function is administered during the stimulation period, although this additional functional recruitment may increase the effectiveness of the ongoing stimulation. Fourth, previous studies used single-blind designs, which may have introduced (unconscious) experimenter bias, thus either over- or underestimating the efficacy of tDCS. In the current study we aim to resolve these methodological caveats. We are currently collecting data from 44 healthy, native German speakers who perform a phonemic and categorical fluency task after having received 20 minutes of 2 mA anodal or sham tDCS over the left prefrontal cortex. The montage is based on electric field simulations to optimally target the left prefrontal cortex, with the anode placed between FC5 and C5 and the cathode placed over AF3 (electrode sizes: 5x5 cm, current density: 0.08 mA/cm²). During stimulation, participants perform a picture naming task for 13 minutes, which is expected to increase neuronal activity in the targeted regions as inferior frontal regions have been shown to be reliably involved in language production. Contrary to previous studies, we will use a double-blind design to ensure both participant and experimenter blinding. If this improved approach effectively decreases between-participant variability with respect to the response to tDCS, we expect higher fluency rates following anodal compared to sham tDCS. By contrast, if tDCS is not effective in modulating verbal fluency performance, no differences should be found between the two tDCS conditions. Thus, the study will provide important fundamental insights into the potential of tDCS to improve higher cognitive functions by investigating the relevance of parameters which may increase the efficacy of this method. Ultimately, these findings will be useful for clinical applications (i.e. language rehabilitation after brain damage) by shedding light on whether tDCS can alleviate language function loss. The study and accompanying hypotheses have been preregistered at the Open Science Framework (https://osf.io/4qmxs/).
Themes: Language Production, Language Therapy
Method: Neurostimulation