The goal of this interventional study is to learn if transcranial direct current stimulation (tDCS), a gentle, cost-effective and non-invasive brain stimulation technique can improve sleep brain activity during an afternoon nap. Since these sleep brain patterns are linked to better memory, attention, and thinking skills, this study aims to find out if improving sleep in a nap can also enhance these cognitive skills in healthy older adults (aged 60+). The main questions it aims to answer are: * Can a short (20-minute) tDCS session before a nap improve sleep patterns during the nap? * Since these sleep patterns are linked to memory and attention, can tDCS also improve thinking skills after the nap? * Are two tDCS session more effective than one for improving nap sleep and thinking skills? Participants will: • Be required to come to the university for testing over four days. During each session they will: * Complete computer based-tasks to assess memory and thinking. * Receive a 20-minute session of either real (active) or fake (placebo) tDCS. * Take a short, monitored nap while researchers measure sleep activity (using polysomnography - a gold-standard, non-invasive sleep monitoring tool). * Complete an easy-to-use sleep test at home on the nights after the naps. * Wear a lightweight watch (called an Actiwatch) throughout the study period to track sleep and movement. * Complete daily sleep diaries. By taking part, participants will help researchers understand whether tDCS can improve sleep during naps and, in turn, support memory and thinking skills. This research could lead to better treatments for sleep problems, help protect brain health, and reduce the risk of dementia as people age. The brain stimulation in this study may also help improve their sleep and cognition.