Effects of Transcranial Electrical Stimulation on Task Performance in Healthy Adults

Preliminary Investigations of Transcranial Electrical Stimulation Effects on Neurophysiology and Behavior

The objective of this randomized, double-blind, sham-controlled, crossover study is to evaluate the effects of transcranial electrical stimulation (tES) on complex cognitive task performance in healthy adult volunteers.

The primary questions this study aims to answer are:

1. Does tES improve task performance, including speed, accuracy, and overall success, during a computerized track-and-capture task?
2. Do different stimulation targets produce differential effects on performance?
3. Are there short-term post-stimulation effects on task performance (up to 48 hours)?

Participants will:

1. Complete two testing sessions under either active or sham stimulation conditions.
2. Perform a complex operational task involving dual-hand controllers while undergoing tES or sham stimulation, and immediately after.
3. Return for follow-up task performance assessments at 24 and 48 hours post-stimulation to evaluate after-effects.

Transcranial electrical stimulation (tES) is a non-invasive neuromodulation technique that delivers low-intensity electrical currents (e.g., <2 mA) through scalp electrodes to modulate brain activity. Numerous studies have shown that tES can enhance cognitive functions such as learning, memory, attention, and decision-making in healthy individuals, as well as provide therapeutic benefits in psychiatric and neurological populations. Despite these findings, substantial knowledge gaps remain regarding the effects of tES, particularly in the context of complex, operationally relevant tasks.

Existing research has primarily focused on the effects of tES on simple cognitive tasks, with limited investigation into task that require multiple cognitive domain to operate simultaneously. Performance on complex tasks, such as those involving motor coordination, visual-spatial process, decision-making, and rapid response, may respond differently to tES than simple, isolated tasks. Understanding these effects could have broad applications in optimizing cognitive performance across various high-demand settings.

This study is designed to address several key uncertainties:

1. Inter-individual variability in behavioral and neurophysiological responses to tES.
2. the impact of stimulation parameters (location, type, intensity) on task performance.
3. The magnitude and duration of both immediate and post-stimulation effects on behavior.

To investigate these questions, healthy adults perform a computerized track-and-capture task requiring real-time motor control and decision-making using dual-hand controllers. Participants undergo both active and sham stimulation in a randomized, double-blind, crossover design. Stimulation will target either the left dorsolateral prefrontal cortex or the left anterior insula, guided by current flow modeling software. Performance is assessed during stimulation, immediately after, and at 24 and 48 hours post-stimulation to evaluate both immediate and short-term after-effects.

Outcome measures include task performance metrics (e.g., speed, accuracy, overall success) and neurophysiological data collected via non-invasive monitoring with functional near-infrared spectroscopy (fNIRS). The study is part of a broader research effort to characterize the functional impact of tES on complex behavior and to inform future applications in cognitive performance enhancement.

All stimulation procedures follow established safety guidelines for low-intensity tES, including continuous monitoring of electrode impedance and post-session adverse event questionnaires assessing discomfort, mood, and cognitive status. The Soterix Medical MXN-33 HD-tES system includes built-in safeguards to prevent excessive current delivery and to ensure safe electrode contact throughout the stimulation. Participants serve as their own controls in a within-subject crossover design, increasing statistical power for detecting within-subject differences between active and sham conditions.

Inclusion Criteria:

• Age 25 to 55 years
• Master's or Doctorate degree, or equivalent relevant experience
• No history of head injury or neurological or psychiatric disorders
• No history of cardiac disease
• No metal implants in the head
• No implanted electronic devices
• Not taking medication affecting neural or cardiovascular function
• Able to provide written, dated informed consent

Exclusion Criteria:

• Smoking within the past year
• Current illegal drug use
• Alcohol abuse
• Pregnancy (confirmed by urine test)
• Participation in another brain stimulation protocol within the past month