Simultaneous tDCS and Computerised Gamified Short-term Memory Task Feasibility

The goal of this observational study is to gain insight into the effects of transcranial direct current stimulation (tDCS) on short-term memory task performance and the feasibility of tDCS in overtly healthy carriers of the susceptibility allele, Apolipoprotein (APOE) ε4, for late-onset Alzheimers disease. The main questions the study aims to answer are: * If tDCS is feasible in overtly healthy APOE ε4 carriers using a headset and an app-based short-term memory task. * If overtly healthy APOE ε4 carriers perform better on a complex short-term memory task when receiving tDCS to the right hemisphere (F4 à PZ) compared to the left hemisphere (F3 à PZ) or sham tDCS. Participants will be asked to complete an app-based short-term memory task while receiving either tDCS to either the right or left hemisphere or sham stimulation on 3 different days spread out over 1-3 weeks.