Yang, Cheng-Chang
(2018)
The effects of repetitive Transcranial Magnetic Stimulation on empathy and impulsivity in healthy adults.
PhD thesis, University of Nottingham.
Abstract
Both impulsivity and empathy are considered crucial in clinical, in particular forensic, populations. A neuroscientific technique, namely repetitive transcranial magnetic stimulation (rTMS), has proven its therapeutic utility in a variety of neuropsychiatric disorders and may be effective in modulating empathy and impulsivity. This thesis aimed to examine the effects of rTMS on empathy and impulsivity in healthy adults via two systematic reviews with meta-analyses and two empirical rTMS studies, thereby contributing to the relatively small pool of knowledge in the field.
The first systematic review and meta-analysis reviewed the literature on the effects of rTMS on empathy in healthy adults, and included 18 studies contributing to 24 effect sizes. The findings revealed an overall small effect favouring active rTMS over sham stimulation on cognitive empathy in healthy individuals. Differential effects across the domains of empathy, namely affective and cognitive empathy (also referred to as theory of mind (ToM)), were evident. Meta-regression revealed no significant between-study heterogeneity in respect of sex ratio, mean age, number of pulses, and stimulation intensity. In conclusion, the study found that rTMS may have discernible effects on different components of cognitive empathy.
The second systematic review and meta-analysis which examined the effects of rTMS on impulsivity in healthy adults included 27 articles consisting of 50 effect sizes. Results indicate that rTMS has distinct effects on different impulsivity subdomains. A small and significant effect was found in respect of modulating motor impulsivity and a moderate effect was found in regards to temporal impulsivity. However, insufficient data was available to ascertain the effects of rTMS on reflection impulsivity.
The first empirical study investigated the effects of excitatory rTMS at the rIFG of 20 healthy male adults in modulating motor and reflection impulsivity. It employed a single-blind randomised crossover design, and it also examined the relationship between trait and behavioural measures of impulsivity. Unexpectedly, no significant effect was found on either motor or reflection impulsivity, after including scores on trait impulsivity as covariates in the analyses. In accord with the extant literature, there were no significant associations between self-report (trait) and behavioural measures of impulsivity.
The final study applied intermittent theta burst stimulation (iTBS) at the left dorsolateral prefrontal cortex (LDLPFC) to modulate cognitive empathy and both temporal and reflection impulsivity in 23 healthy adults, using a single-blind randomised crossover design. Non-significant post-iTBS effects on both cognitive empathy and impulsivity were found. Baseline trait measures of empathy and impulsivity were included in the analysis as covariates in order to control for the impact of pre-stimulation individual differences on the iTBS modulation.
Despite the mixed results, I argue that rTMS can potentially be used to modulate empathy and impulsivity. Future studies in the field should address some of the limitations highlighted in this project, for instance, in terms of localisation of stimulation sites, stimulation parameters and sample sizes, to determine the utility of TMS.
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