Investigating the Effectiveness of a 2-week Novel Non-invasive Brain Stimulation Technique on Cognitive Outcomes in Healthy Adults

Investigating the Effectiveness of a 2-week High-frequency Transcranial Pulsed-current Stimulation on Cognitive Outcomes in Healthy Adults: A Randomised, Double Blinded, Sham-controlled Study

The goal of this randomised controlled trial is to investigate the effects of a 2-week high-frequency transcranial pulsed current stimulation (tPCS) on cognitive outcomes in older and healthy adults. The main questions it aims to answer are:

1. Would a single session of anodal tPCS over the left prefrontal cortex improve working memory, task inhibition, and task switching in healthy young and older adults, compared to anodal transcranial direct current stimulation (tDCS) and sham-tPCS?
2. Would repeated session of anodal-tPCS (2-weeks) lead to improvements in working memory, task inhibition, and task switching in healthy young and older adults, compared to tDCS and sham-tPCS?
3. Will tPCS be better tolerated among healthy adults, compared to tDCS?

Researchers will compare tPCS / tDCS / sham-tPCS to see if there are any differences in cognitive outcomes after 1 session and after repeated sessions, as well as to compare the tolerance of tPCS against tDCS and sham-tPCS.

Participants will be requested to:

• Undergo 1 of 3 of the following conditions: tDCS / tPCS / sham-tPCS
• Complete three sessions of cognitive tasks testing working memory, inhibition and task switching at baseline (pre-stimulation), after day 1 of brain stimulation and after 10 sessions of brain stimulation (post- repeated stimulation)
• Undergo fNIRS-EEG brain measurements concurrently with the cognitive tasks

tPCS / tDCS and sham-tPCS will be administered between 0.6 to 0.7 mA for 20 minutes. This will take place over 10 consecutive sessions, with a 2 day break between days 5 and 6 of brain stimulation. The setup of the stimulation consists of a saline-soaked sponge anode electrode placed over the left forehead area over the left dorsal lateral prefrontal cortex, and the cathode will be placed over the right parietal cortex. Participants will be randomly assigned to 1 of 3 conditions and this will be blinded to both the participants and the researcher (double-blinded).

Cognitive tasks will be administered at baseline, after 1 session of stimulation and after 10 sessions of stimulation (post-stimulation). These cognitive tasks consist of a working memory task (1/2/3 back tasks), a cognitive inhibition task (go/no-go task) and a cognitive flexibility task (Stroop task). Concurrent with the cognitive task will be the administration of fNIRS-EEG recording to measure changes in brain activation and patterns during the tasks.

The experiment will take place in the Motor Behaviour Lab at the National Institute of Education, Nanyang Technological University in Singapore.

Inclusion Criteria:

• Male and female young (21 to 30 years) and older adults (60 to 75 years)
• Right-handed
• Must be a native English speaker
• No clinical diagnosis of neurodevelopmental, mood, neurological or neurodegenerative disorders
• Adults with cardiometabolic or cardiovascular conditions may participate if their condition is controlled and stable with medication and / or lifestyle interventions

Exclusion Criteria:

• Currently on long-term medication for pain or migraines / headaches
• Adults with metallic implants in the chest or head region
• Adults with epilepsy, or known seizure or immediate family members that have had a seizure before
• Had a recent head injury that resulted in a temporary loss of consciousness or of memory in the last 12 months
• Had prior head surgery
• Prone to fainting
• Sensitive skin or prone to skin allergies