Effects of Non-Invasive Brain Stimulation on Soldiers' Cognitive and Functional Performance

Study Overview
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Brief Summary
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Non-invasive brain stimulation has been shown to alter performance in both clinical and healthy populations on cognitive tasks. While the performance alterations have generally been shown to result in enhancement, mixed results remain in the literature. Much of the mixed results within the literature have been attributed to the use of different stimulation parameters, targeting of different brain areas, and using a variety of performance measures or assessing different constructs. However, non-invasive brain stimulation is a desirable method for enhancing Soldier performance given the ease of administration and minimal side effects as compared to other forms of performance enhancement (e.g., pharmaceuticals, caffeine). The objective of the current study is to evaluate the effects of non-invasive brain stimulation to the left dorsolateral prefrontal cortex in enhancing Soldier cognitive skills and performance on military tasks. A double blind within-subjects design will be used with healthy, rested Soldiers who will receive non-invasive brain stimulation and perform basic cognitive and operationally relevant tasks.

Official Title
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Effects of Non-Invasive Brain Stimulation on Soldiers' Cognitive and Functional Performance

Conditions
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Performance Enhancement

Intervention / Treatment
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* Device: Transcranial direct current stimulation


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Must be 18 (if active duty), 19 (if non-active duty) up to 40 years old. Must have normal hearing, vision or corrected to normal vision, and cognitive function as determined by self-report and screening by study physician Must have obtained at minimum 6 hours of sleep prior to data collection, as assessed by actigraphy data and self-report. Must have refrained from consumption of caffeine, 16 hours, nicotine, 2 hours, and alcohol, 24 hours, prior to the study, assessed by self-report. Exclusion Criteria: The following medically-related exclusionary criteria will be used, as assessed and verified by the study physician: Haven taken any medications which induce drowsiness, such as over-the-counter antihistamines within 24 hours of participation in the study. Any self-medication will be assessed through self-report No current medical conditions or medications affecting cognitive function or attention. Any history of any attention deficit condition requiring medication. Any history of psychological/psychiatric disorder. Any history of seizures, migraines, or neurological disorders. History of a head injury involving loss of consciousness. Any metal implanted within the head (e.g., shrapnel, surgical clips) or any implanted devices (e.g., cardiac pacemaker, brain stimulator, hydrocephalic shunt). Skin condition on the scalp, such as psoriasis or eczema, or wounds on the head. Currently receiving hormonal therapy treatments, other than birth control or as determined by physicians. Potential for caffeine withdrawal symptoms that will impede cognitive testing. Females with a known pregnancy, who test positively for pregnancy, or refuse the test will be excluded, given the lack of available research regarding the effects of tDCS during pregnancy. Known pregnancy will be assessed during screening, females without a known pregnancy will be requested to provide a urine sample during the screening procedures to ensure the absence of pregnancy.

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 40 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Crossover Assignment
Interventional Model Description: A double-blind, randomized, sham-controlled, within-subjects design
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Active anodal stimulation<br>active anodal stimulation at F3, cathode placed on contralateral bicep | Device: Transcranial direct current stimulation<br>* Transcranial direct current stimulation (tDCS) is a form of non-invasive brain stimulation that stimulates the brain through the application of a low-intensity electrical current, typically ranging from 1 to 2 milliamps (mA), via electrodes placed on an individual's scalp. During the active stimulation sessions, 2 mA of stimulation will be applied for 30 minutes. During the sham stimulation session, 2 mA of stimulation will be applied over the course of 90 sec, the electrodes will remain in place for the 30 minute duration.<br>|
| Experimental: Active cathodal stimulation<br>active cathodal stimulation at F3, anode placed on contralateral bicep | Device: Transcranial direct current stimulation<br>* Transcranial direct current stimulation (tDCS) is a form of non-invasive brain stimulation that stimulates the brain through the application of a low-intensity electrical current, typically ranging from 1 to 2 milliamps (mA), via electrodes placed on an individual's scalp. During the active stimulation sessions, 2 mA of stimulation will be applied for 30 minutes. During the sham stimulation session, 2 mA of stimulation will be applied over the course of 90 sec, the electrodes will remain in place for the 30 minute duration.<br>|
| Sham Comparator: Sham stimulation<br>sham stimulation that will be counterbalanced between subjects such that half will receive sham stimulation configured as condition 1 (anode F3, cathode bicep) and half will receive condition 2 (cathode F3, anode bicep) | Device: Transcranial direct current stimulation<br>* Transcranial direct current stimulation (tDCS) is a form of non-invasive brain stimulation that stimulates the brain through the application of a low-intensity electrical current, typically ranging from 1 to 2 milliamps (mA), via electrodes placed on an individual's scalp. During the active stimulation sessions, 2 mA of stimulation will be applied for 30 minutes. During the sham stimulation session, 2 mA of stimulation will be applied over the course of 90 sec, the electrodes will remain in place for the 30 minute duration.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Military task performance | Patrol exertion multitask | Folllowing stimulation; task lasts approximately 20 min | 
| Military task performance | Target acquisition | Folllowing stimulation; task lasts approximately 40 min | 
| Cognitive function - Selective Attention | Stroop test | Approximately 3 minutes during stimulation | 
| Cognitive function - Multitasking/Working Memory | Dual n-back | Approximately 5 minutes during stimulation | 
| Cognitive function - Working Memory | Digit span task | Approximately 2 minutes during stimulation | 
| Cognitive function - Sustained attention | Rapid Visual Information Processing Task | Approximately 7 minutes during stimulation | 
| Cognitive function - Executive function | Shifting Attention Task: Digit symbol substitution task | Approximately 2 minutes during stimulation | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Cognitive function - Impulsivity/Motor Control | Stop signal task - response inhibition | Approximately 3 minutes after stimulation | 
| Cognitive function - Risk Taking/ Decision Making | Delayed Discounting Task | Approximately 1 minute after stimulation | 
| Cognitive function - Cognitive Flexibility | Uses Task | Approximately 5 minutes after stimulation |