Exploring the Role of the Prefrontal Cortex in Decision-Making

The goal of this study is to examine whether high-definition transcranial direct current stimulation (HD-tDCS) can influence decision-making for emotionally valenced content in younger and older adults, with or without major depression. The main questions are: In healthy adults, does brain stimulation modulate how people respond to emotionally valenced content during a decision-making task? What happens in the brain during modulation? Do these effects differ between younger and older adults? In adults with depression, does brain stimulation help shift attention towards positive content during the task? What happens in the brain? Are these effects moderated by age (younger vs. older adults)? The investigators will compare participants who receive real stimulation to those who receive sham (placebo) stimulation. Participants will: Receive high-definition transcranial direct current stimulation (HD-tDCS) of the dorsolateral prefrontal cortex (DLPFC) Perform a decision-making task involving emotionally valenced words Complete the task while undergoing a brain scan using ultra-high field 7 Tesla magnetic resonance imaging (MRI) to measure brain activity