Utilizing Transcranial Direct Current Stimulation (tDCS) to Boost Social Pleasure and Participation in Older Lonely Individuals

This randomized clinical trial aims to test the effects of 10 sessions of transcranial direct current stimulation (tDCS) on social and emotional functions in lonely older adults. The main objectives include: * Understand whether tDCS could successfully boost positive social processing and social motivation in older adults, paralleling its effect on non-social reward processing; * Understand whether the reduced negative and increased positive social processing in older adults would translate to an increase in real-life social activity and a decrease in loneliness feeling; * Examine the intervention efficacy of tDCS among the aged population; * Understand whether the tDCS effect could be long-lasting (i.e., 1 and 3 months after intervention). Participants will be lonely older adults aged 60 or above and screened on inclusion and exclusion criteria. Eligible participants will be randomly allocated to the left dorsolateral prefrontal cortex (DLPFC) tDCS group, the right ventrolateral prefrontal cortex (VLPFC) tDCS group, or the sham control group. Participants will complete an Emotion Rating Task, questionnaires assessing their psychosocial functions, and neuropsychological tests assessing their cognitive functions at baseline, after the 5th stimulation session, immediately after the 10th stimulation session, and 1 month and 3 months after the 10th stimulation session.