How does tyrosine intake influence brain stimulation effects on working memory and planning?

INTERVENTION: In this study, all participants will first complete a dietary screener questionnaire to capture average weekly tyrosine consumption. Second, they will then complete two well‐established neuropsychological measure of working memory known (Corsi Blocks) and planning (Tower of London). The tests will be administered in the lab using a piece of software called PEBL. Third, they will undergo three different types of non‐invasive brain stimulation: A) active transcranial direct current stimulation (tDCS) of the dorsolateral prefrontal corte X(dlPFC) with the anode placed on the left and the cathode placed on the right hemisphere; B) active transcranial random noise stimulation (tRNS) with the electrodes placed in the same position as tDCS: C) sham/non‐active stimulation. The order of non‐invasive brain stimulation allocation will be randomized for each participant. To avoid potential carryover effects of non‐invasive brain stimulation, as this is a crossover design, each session will be separated by at least 72 hours. For active tDCS, a current at 1.5 mA will be delivered for 10 minutes while the participant is relaxed plus the additional duration of the participant completing the Corsi Blocks and Tower of London test (approximately 10 minutes) with additional 30‐second fade‐in/fade‐out periods. For active tRNS, a digital high‐pass filter is used to damp frequencies below 100 Hz, and deliver frequencies between 100 Hz to 640 Hz, with a maximum possible current set at 1.5 mA. For sham, the stimulation will include only the initial 30‐second ramp‐up protocol to mimic active non‐invasive brain stimulation and ramp down. Masking of the conditions will be achieved using the neuroConn study mode. Testing will be carried out by three honours r CONDITION: Cognitive impairment; ; Cognitive impairment Neurological ‐ Other neurological disorders Neurological ‐ Studies of the normal brain and nervous system PRIMARY OUTCOME: Corsi Blocks memory span[Immediately before non‐invasive brain stimulation (tDCS, tRNS or sham) and 10 minutes following brain stimulation onset across three experimental sessions.] Tower of London number of moves[Immediately before non‐invasive brain stimulation (tDCS, tRNS or sham) and 10 minutes following brain stimulation onset across three experimental sessions.] SECONDARY OUTCOME: Corsi Blocks reaction times.[Immediately before non‐invasive brain stimulation (tDCS, tRNS or sham) and 10 minutes following brain stimulation onset across three experimental sessions.] Tower of London total time.[Immediately before non‐invasive brain stimulation (tDCS, tRNS or sham) and 10 minutes following brain stimulation onset across three experimental sessions.] INCLUSION CRITERIA: • You are aged between 18 and 50 years (the upper age limit of 50 years has been selected as there is some evidence that mild cognitive decline begins past this age) • You are in good health • You agree to fast 3 hours prior to testing (only water or herbal tea allowed) (glucose levels are known to modulate performance in several cognitive domains. By having all participants fast for 3 hours prior to testing, we can rule out an enhancing effect of glucose on the cognitive tasks).