Modulating eating behaviour with transcranial direct current stimulation (tDCS): Towards effective study design, stimulation parameters and participant characteristics

Across prior studies using transcranial direct current stimulation (tDCS) to modulate eating behaviour there is heterogeneity in study design, tDCS parameters, and participant characteristics. This variation has led to equivocal findings. The present thesis considered the impact of this variation on eating-related outcomes (subjective appetite, food craving, food reward), and looked to identify the presence of an effect of tDCS with the aim of establishing consistency and replicability in the application of stimulation, with onward use as a modality for modulating eating behaviours and potentially as a tool in weight management. To consider the impact of heterogeneous stimulation parameters, a systematic literature review and meta-analysis was conducted. This review considered the most comprehensive list of tDCS parameters to date and identified a series of parameters that produce a more consistent reduction across eating-related measures. These parameters were applied in two empirical studies exploring the impact of varying participant characteristics. As part of this, a second systematic review and meta-analysis was conducted. This identified a potential eating behaviour trait-dependent effect where those with traits suggesting susceptibility to overconsumption and weight gain (e.g., binge eating behaviour) appear most responsive to the effects of tDCS. The empirical studies provided further data on this trait-dependent effect by comparing the effects of tDCS across two populations; “healthy” individuals (i.e., those who do not display susceptibility to overconsumption) and those with binge-type behaviour. No changes across eating-related measures were observed when comparing active versus sham tDCS across both participant populations. This is largely supported by anecdotal-to-strong evidence in favour of the null hypothesis as indicated by Bayesian analyses. The novel and original contributions of this thesis include establishing a comprehensive set of tDCS parameters that appear to produce consistent modulation of eating behaviours, and consideration for the eating behaviour trait-dependent effect of tDCS through meta-analytic and empirical data. These findings provide a clear direction for future work exploring the use of tDCS as a modality for the control of eating behaviours, including recommendations for the consistent application of tDCS in this domain.