Modulatory effects of physical exercise and transcranial electrical brain stimulation on long-term memory and their associated neural oscillatory activity

By providing a standardised design, this thesis aimed to determine the most effective physical exercise (PE) protocol for long-term memory enhancement, whilst directly comparing it to active rest (AR) and passive rest (PR). Concurrently, EEG was recorded during PE to investigate correlations between neural oscillations and enhanced memory performance. Additionally, some studies demonstrated positive effects of transcranial direct current stimulation (tDCS) on declarative memory. Therefore, the effects of PE and tDCS were compared. Further, this was also the first time that acute PE and tDCS were combined into one intervention to investigate whether their combination would elicit further increases in memory modulation.

In six studies, 181 participants memorised a series of images and were tested using an old/new recognition task. In studies 1-3, effects of different PE protocols and intensities were compared together and with AR and PR. Study 4 compared the effects of tDCS to moderate- intensity PE and PR. Studies 5 and 6 compared the effects of moderate-intensity PE to the combined intervention after retention intervals of 90 min and 24h.

Moderate-intensity PE yielded the greatest enhancements to memory performance compared to PR when tested after 90 min, but not after 24h. While tDCS and PE enhanced memory, the combined intervention impaired memory. Finally, negative correlations between alpha and parietal beta oscillations were correlated to successful memory enhancement, whereas positive correlations between theta, gamma, and frontal beta were correlated with successful memory enhancement. These studies show PE as a potentially successful method of memory enhancement and highlight the complexity of mechanism of action of PE and tDCS in memory enhancement. Together, these findings could have significant implications in the treatment of memory deficiencies. Furthermore, these findings show that tDCS modulates memory similarly to PE, with possible benefits for at-home applications and for people unable to participate in PE.