Closed-loop Brain Stimulation

The goal of this study is to establish if non-invasive closed-loop neuromodulation is an effective approach to enhance cognitive function in healthy 18-40 years old volunteers. The main questions it aims to answer are: * Can closed-loop stimulation increase stimulation effectiveness? * Can closed-loop focused ultrasound specifically engage with excitatory or inhibitory neural populations in the target structure as measured through MRS? * Can observed stimulation outcomes for FUS be predicted through connectome analysis and computational models of indirect changes? Researchers will compare different closed-loop options to their open-loop counterpart to see if closed-loop approaches can increase efficacy and reduce the variability of the stimulation compared to open-loop approaches. Participants will: * Answer some questionnaires at the start of the study and after each intervention session. * Undertake a MRI scanning session. * Undertake one open-loop FUS session. * Undertake one tES session. * Undertake one closed-loop FUS sessions involving tES and FUS, followed by a MRI scanning * Undertake one sham FUS session * Attend one visit in person to assess eligibility through questionnaires and one cognitive task