An investigation into the impact of cumulative life stress and neuromodulation on adults’ cognitive function and subjective well-being.

As healthcare advances, more people are living longer increasing the prevalence of age-related disorders including declining brain function. Acute and chronic stress can also negatively affect brain activity however less is known about the impact of accumulated stress and its interaction with ageing. Interventions that best maintain brain and cognitive health, e.g. exercise and calorie-restriction, are not suitable for everyone. This research aimed to understand the impact of healthy ageing, cumulative stress and their interaction on executive function and subjective well-being and also to identify and investigate practical interventions. A literature review indicated mindfulness meditation (MM) and transcranial alternating current stimulation (tACS) as appropriate interventions. Their relative efficacy were systematically reviewed and meta-analysed. The following studies were then completed which targeted healthy adults aged 18-85: Study 1 aimed to replicate the finding that cumulative life stress accelerates cognitive ageing as well as evaluate the efficacy of tACS as potential mitigation. Studies 2A and 2B aimed to replicate and confirm Study 1’s findings. Study 3 measured the impact of ageing, cumulative stress, resilience and subjective sleep quality on working memory. It also explored the impact of adverse childhood events and it’s interaction with cumulative stress on working memory. In Study 4, the well-used cumulative stress index, Social Readjustment Rating Scale (SRRS), central to this work, was modernised and updated whilst remaining compatible with the original, i.e. backwards-compatible. Analyses were conducted with Bayesian and frequentist statistics. Key meta-analysis findings were a lack of rigour in MM research and no conclusive benefit to subjective well-being or working memory; a lack of standardised protocols in tACS research but an indication that sophisticated tACS protocols can be effective. Key findings for Studies 1 to 3 showed no evidence that cumulative stress has an accelerative ageing effect. However, ageing slowed processing speed. Resilience increased with age. There were no associations between working memory and the independent variables. Study 4 successfully updated and modernised the SRRS. This thesis provides preliminary evidence that higher levels of cumulative life stress, as measured with the SRRS, are unlikely to accelerate the ageing of older adults’ cognitive functioning. It also demonstrates that to draw conclusions in these areas, overall research standards need to be raised by improving rigour and standardisation, employing sophisticated tACS protocols and using an updated, backwards-compatible SRRS. In addition, data collected may serve as an informed Bayesian prior.