Closed-loop tES-non-invasive 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

Inclusion Criteria: * Participant is willing and able to give informed consent for participation in the study * Aged between 18 and 40 * Good general health * Not consume alcohol 48 hours prior study visit * Not currently taking any medications (except contraceptive pills) or if on long-term medication for a non-neurological/non-psychiatric condition (r.g. inhalers) to be considered otherwise healthy and stable with no symptoms * Be right handedness Exclusion Criteria: * Inability to complete MRI/FUS/TMS/tES safety questionnaire and / or informed consent process. * Current or previous diagnosis of a neurological, neurosurgical, psychiatric disorders. * Other significant medical condition (specific details to be reviewed by the CI prior to inclusion). * Currently pregnant, breast feeding, or on planned pregnancy. * Medication intake (such as beta-blocker, glucocorticoids, anti-depressants, anti-inflammatory drugs in the last 7d). * Medication intake (such as beta-blocker, glucocorticoids, anti-depressants) in the last 7d that are likely to affect brain function. * Significant use of medication or recreational drugs that affect the nervous system. * Excessive consumption of alcohol (\>2 alcohol beverages per day). * Known allergy to any required consumables (such as aquasonic gel). * History of anaphylaxis to any substance * Have tightly coiled, curly or voluminous texture hair type (e.g., hair type 3, 4, or afro hair). * Having skin disease or sensitive skin on or close to the head.