Detecting functional deficits following sub-concussive head impacts: the relationship between head impact kinematics and visual-vestibular balance performance.

Introduction: Mild traumatic brain injury (mTBI) continues to be a significant issue facing the US military. While TBI cases in deployed environments are of significant concern, an estimated 80% of diagnoses occur in garrison settings (e.g., military training).Objective: With the aim of improving the detection of potentially concussive exposures, the objective of this study was to evaluate the relationships between head impact kinematics and performance on a visual-vestibular balance task.Methods: Participants (n = 51) were enrolled in the Basic Airborne Training Course. Two sensors to measure head impacts sustained were worn. Performance was measured at four time points: baseline and at the end of each week of the course.Results: Visual-vestibular balance task performance tended to decrease over the course of airborne training for our participants, however, limited to the most challenging levels of the task. Also, head impact kinematic measures correlated with performance outcomes to suggest that worse performance was associated with greater number of impacts and greater linear and rotational acceleration and rotational velocity.Discussion: Our findings suggest that visual-vestibular balance task performance may be a useful measure for detection of sub-concussive impacts and that wearable sensors may provide useful data on head impact kinematics that relates directly to functionally relevant performance.

Measuring the Domain Specificity of Workload Using EEG: Auditory and Visual Domains in Rotary-Wing Simulated Flight.

OBJECTIVE: The overarching objective was to evaluate whether workload sensory-domain specificity could be identified through electroencephalogram (EEG) recordings during simulated rotary-wing operations. BACKGROUND: Rotary-wing aviators experience workload from different sensory domains, although predominantly through auditory and visual domains. Development of real-time monitoring tools using psychophysiological indices, such as EEG recordings, could enable identification of aviator overload in real time. METHOD: Two studies were completed, both of which recorded EEG, task performance, and self-report data. In Study 1, 16 individuals completed a basic auditory and a basic visual laboratory task where workload was manipulated. In Study 2, 23 Army aviators completed simulated aviation flights where workload was manipulated within auditory and visual sensory domains. RESULTS: Results from Study 1 found differences in frontal alpha activity during the auditory task, and that alpha and beta activities were associated with perceived workload. Frontal theta activity was found to differ during the visual task while frontal alpha was associated with perceived workload. Study 2 found support for frontal beta activity and the ratio of beta to alpha + theta to differentiate level of workload within the auditory domain. CONCLUSION: There is likely a role of frontal alpha and beta activities in response to workload manipulations within the auditory domain; however, this role becomes more equivocal when examined in a multifaceted flight scenario. APPLICATION: Results from this study provide a basis for understanding changes in EEG activity when workload is manipulated in sensory domains that can be used in furthering the development of real-time monitoring tools.

Evaluation of the Military Functional Assessment Program: Preliminary Assessment of the Construct Validity Using an Archived Database of Clinical Data.

BACKGROUND: Several important factors must be considered when deciding to return a soldier to duty after a traumatic brain injury (TBI). Premature return increases risk for not only second-impact syndrome during the acute phase but also permanent changes from repetitive concussions. Thus, there is a critical need for return-to-duty (RTD) assessment criteria that encompass the spectrum of injury and disease experienced by US soldiers, particularly TBI. OBJECTIVES: To provide evidence-based standards to eventually serve as criteria for operational competence and performance of a soldier after injury. Specifically, the relationships between clinical assessments and novel military-specific tasks were evaluated. METHOD: Exploratory analyses (including nonparametric tests and Spearman rank correlations) of an archived database. PARTICIPANTS: A total of 79 patients with TBI who participated in an RTD assessment program at a US Army rehabilitation and recovery center. MAIN MEASURES: Military Functional Assessment Program (to determine a soldier's operational competence and performance after TBI) tasks; Dizziness Handicap Inventory; Dynamic Visual Acuity (vestibular function); Sensory Organization Test (postural control); Repeatable Battery for the Assessment of Neuropsychological Status (neuropsychological screening test); Beck Depression Inventory-II; Beck Anxiety Inventory; Comprehensive Trail Making Test (visual search and sequencing); posttraumatic stress disorder checklist military version; Alcohol Use Disorders Identification Test; Epworth Sleepiness Scale; Patient Health Questionnaire; and Military Acute Concussion Evaluation. RESULTS: Selected military operational assessment tasks correlated significantly with clinical measures of vestibular function, psychological well-being, and cognitive function. Differences on occupational therapy assessments, a concussion screening tool, and a self-report health questionnaire were seen between those who passed and those who failed the RTD assessment. Specifically, those who passed the RTD assessment scored more favorably on these clinical assessments. CONCLUSIONS: This study demonstrated convergent validity between Military Functional Assessment Program tasks and clinical assessment scores. The Military Functional Assessment Program shows promise for augmenting decision making related to RTD and soldier skills. Additional research is needed to determine the effectiveness of this program in predicting RTD success.

Comparison of the effects of ketamine and morphine on performance of representative military tasks.

BACKGROUND: When providing care under combat or hostile conditions, it may be necessary for a casualty to remain engaged in military tasks after being wounded. Prehospital care under other remote, austere conditions may be similar, whereby an individual may be forced to continue purposeful actions despite traumatic injury. Given the adverse side-effect profile of intramuscular (i.m.) morphine, alternative analgesics and routes of administration are of interest. Ketamine may be of value in this capacity. OBJECTIVES: To delineate performance decrements in basic soldier tasks comparing the effects of the standard battlefield analgesic (10 mg i.m. morphine) with 25 mg i.m. ketamine. METHODS: Representative military skills and risk propensity were tested in 48 healthy volunteers without pain stimuli in a double-blind, placebo-controlled, crossover design. RESULTS: Overall, participants reported more symptoms associated with ketamine vs. morphine and placebo, chiefly dizziness, poor concentration, and feelings of happiness. Performance decrements on ketamine, when present, manifested as slower performance times rather than procedural errors. CONCLUSIONS: Participants were more symptomatic with ketamine, yet the soldier skills were largely resistant to performance decrements, suggesting that a trained task skill (autonomous phase) remains somewhat resilient to the drugged state at this dosage. The performance decrements with ketamine may represent the subjects' adoption of a cautious posture, as suggested by risk propensity testing whereby the subject is aware of impairment, trading speed for preservation of task accuracy. These results will help to inform the casualty care community regarding appropriate use of ketamine as an alternative or opioid-sparing battlefield analgesic.

Tactile cues in continuous operations: a preliminary study.

INTRODUCTION: Research has shown that tactile displays are an effective tool for augmenting spatial orientation and situation awareness information provided to aircraft operators. The tactile situation awareness system (TSAS) has been shown to improve flight performance in conditions of degraded visual environments and to safely maintain performance during hover over moving targets. The potential for the user to adapt and habituate to the stimulus of tactile display systems has not yet been investigated. METHODS: Four UH-60 current, rated aviators (all male) participated in the pilot study. Subjects completed four consecutive iterations of a 3-h flight profile consisting of 10 maneuvers, totaling 12 h of continuous flight. Flight performance, tactor information, responses to a discomfort questionnaire, and ratings of fatigue symptoms were recorded. RESULTS: The independent variable in all analyses was session (four levels). The results showed that performance per maneuver and proportion of stimulus cues (measure of response to cues) per maneuver were consistent across sessions using independent-samples Kruskal-Wallis tests. DISCUSSION: The findings of this preliminary assessment support the use of tactile displays (consistent with parameters of TSAS) in continuous operations since performance and proportion of stimulus cues presented was consistent over a period of 12 h. In conclusion, the system will require further experimental testing, but these preliminary findings do not suggest performance or response to be affected by any adaptation or habituation to the stimulus.

Transcranial Direct Current Stimulation and Aviator Performance During Simulated Flight.

INTRODUCTION: Transcranial direct current stimulation (tDCS) is a promising method for maintaining cognitive performance. Anticipated changes in rotary-wing aircraft are expected to alter aviator performance.METHODS: A single-blind, randomized, sham-controlled study evaluated effects of 2-mA anodal tDCS to the right posterior parietal cortex on aviator performance within a Black Hawk simulator. A mixed design with one between-subjects factor was assessed: stimulation prior to flight (20 constant min) and during flight (two timepoints for 10 min each). The within-subjects factor included active vs. sham stimulation. Randomly assigned to each stimulation group were 22 aviators. Aircraft state metrics derived from the simulator were used to evaluate performance. Subjects completed two flights (active stimulation and sham stimulation) with an in-flight emergency introduced at the end to assess whether the timing of tDCS application (prior or during flight) affected the ability to maintain attention and respond to an unexpected event.RESULTS: Results found active stimulation during flight produced statistically significant improvements in performance during the approach following the in-flight emergency. Subjects maintained a more precise approach path with glideslope values closer to zero (M = 0.05) compared to the prior-to-flight group (M = 0.15). The same was found for localizer values (during flight, M = 0.07; prior to flight, M = 0.17). There were no statistically significant differences between groups on secondary outcome measures.DISCUSSION: These findings suggest stimulation during flight may assist in maintaining cognitive resources necessary to respond to an unexpected in-flight emergency. Moreover, blinding efficacy was supported with 32% of subjects correctly guessing when active stimulation was being delivered (52% correctly guessed the sham condition).Feltman KA, Kelley AM. Transcranial direct current stimulation and aviator performance during simulated flight. Aerosp Med Hum Perform. 2024; 95(1):5-15.

Measuring aviator workload using EEG: an individualized approach to workload manipulation.

Introduction: Measuring an operator's physiological state and using that data to predict future performance decrements has been an ongoing goal in many areas of transportation. Regarding Army aviation, the realization of such an endeavor could lead to the development of an adaptive automation system which adapts to the needs of the operator. However, reaching this end state requires the use of experimental scenarios similar to real-life settings in order to induce the state of interest that are able to account for individual differences in experience, exposure, and perception to workload manipulations. In the present study, we used an individualized approach to manipulating workload in order to account for individual differences in response to workload manipulations, while still providing an operationally relevant flight experience. Methods: Eight Army aviators participated in the study, where they completed two visits to the laboratory. The first visit served the purpose of identifying individual workload thresholds, with the second visit resulting in flights with individualized workload manipulations. EEG data was collected throughout both flights, along with subjective ratings of workload and flight performance. Results: Both EEG data and workload ratings suggested a high workload. Subjective ratings were higher during the high workload flight compared to the low workload flight (p < 0.001). Regarding EEG, frontal alpha (p = 0.04) and theta (p = 0.01) values were lower and a ratio of beta/(alpha+theta) (p = 0.02) were higher in the baseline flight scenario compared to the high workload scenario. Furthermore, the data were compared to that collected in previous studies which used a group-based approach to manipulating workload. Discussion: The individualized method demonstrated higher effect sizes in both EEG and subjective ratings, suggesting the use of this method may provide a more reliable way of producing high workload in aviators.

Limitations associated with transcranial direct current stimulation for enhancement: considerations of performance tradeoffs in active-duty Soldiers.

Introduction: Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation method, popular due to its low cost, ease-of-application, and portability. As such, it has gained traction in examining its potential for cognitive enhancement in a diverse range of populations, including active-duty military. However, current literature presents mixed results regarding its efficacy and limited evaluations of possible undesirable side-effects (such as degradation to cognitive processes). Methods: To further examine its potential for enhancing cognition, a double-blind, randomized, sham-controlled, within-subjects design, was used to evaluate both online active-anodal and -cathodal on several cognitive tasks administered. Potential undesirable side effects related to mood, sleepiness, and cognitive performance, were also assessed. Active tDCS was applied for 30 min, using 2 mA, to the left dorsolateral prefrontal cortex with an extracephalic reference placed on the contralateral arm of 27 (14 males) active-duty Soldiers. Results: We report mixed results. Specifically, we found improvements in sustained attention (active-anodal) for males in reaction time (p = 0.024, ηp 2 = 0.16) and for sensitivity index in females (p = 0.013, ηp 2 = 0.18). In addition, we found faster reaction time (p = 0.034, ηp 2 = 0.15) and increased accuracy (p = 0.029, ηp 2 = 0.16) associated with executive function (active-anodal and -cathodal), and worsened working memory performance (active-cathodal; p = 0.008, ηp 2 = 0.18). Additionally, we found increased risk-taking with active-anodal (p = 0.001, ηp 2 = 0.33). Discussion: tDCS may hold promise as a method for cognitive enhancement, as evidenced by our findings related to sustained attention and executive function. However, we caution that further study is required to better understand additional parameters and limitations that may explain results, as our study only focused on anode vs. cathode stimulation. Risk-taking was examined secondary to our main interests which warrants further experimental investigation isolating potential tradeoffs that may be associated with tDCS simulation.

Tactile cues for orienting pilots during hover over moving targets.

INTRODUCTION: Providing information via the tactile sensory system allows the pilot to increase awareness without further taxing the visual and auditory perceptual systems. In this study, tactile cues were presented to pilots for target orientation during a simulated helicopter extraction over a moving target. The efficacy of the cues provided by the tactile system was assessed under various conditions (rested vs. fatigued, clear vs. degraded visual environment). METHODS: This study employed a mixed-model 2(4) factorial design, including one between-subjects variable (training amount: minimal, additional) and three within-subjects variables (state: rested, fatigued; visual environment: clear, degraded; tactile cue belt: active, inactive). Across 2 d under the 4 test conditions, 16 UH-60 rated, healthy aviators completed 8 sessions of 10-min stabilized hovering maneuvers over a moving target. All flights were conducted in a UH-60 flight simulator. RESULTS: Subjects were able to stay closer to the target when the tactile cuing system was active (M = 31.14 ft, SE = 3.17 ft) vs. inactive (M = 36.33 ft, SE = 2.84 ft). Likewise, subjects rated their situation awareness as greater when the tactile system was active vs. inactive. DISCUSSION: The results support the efficacy of the tactile system in providing directional cues for maintaining pilot performance during a hover maneuver over a moving target.

Preliminary Evaluation of an Osteopathic Manipulative Treatment to Prevent Motion Sickness.

INTRODUCTION: Motion sickness affecting military pilots and aircrew can impact flight safety and, if severe, can lead to disqualification from flight status. However, due to the common adverse effects of motion sickness pharmaceuticals (e.g., drowsiness), medication options are severely limited. The purpose of this study was to explore the potential utility of a nonpharmaceutical method for motion sickness prevention, specifically an osteopathic manipulative technique (OMT).METHODS:A novel OMT protocol for the reduction of motion sickness symptoms and severity was evaluated using a sham-controlled, counterbalanced, between-subjects study design. The independent variable was OMT treatment administered prior to the motion sickness-inducing procedure (rotating chair). The primary dependent measures were total and subscale scores from the Motion Sickness Assessment Questionnaire.RESULTS:The OMT treatment group experienced significantly fewer gastrointestinal (mean scores postprocedure, treatment M = 20.42, sham M = 41.67) and sopite-related (mean scores postprocedure, treatment M = 12.81, sham M = 20.68) symptoms than the sham group while controlling for motion sickness susceptibility. There were no differences between groups with respect to peripheral and central symptoms.DISCUSSION:The results suggest that the treatment may prevent gastrointestinal (nausea) and sopite-related symptoms (sleepiness). These preliminary findings support further exploration of OMT for the prevention of motion sickness. A more precise evaluation of the mechanism of action is needed. Additionally, the duration of the effects needs to be investigated to determine the usefulness of this technique in training and operational settings.Thomas VA, Kelley AM, Lee A, Fotopoulos T, Boggs J, Campbell J. Preliminary evaluation of an osteopathic manipulative treatment to prevent motion sickness. Aerosp Med Hum Perform. 2023; 94(12):934-938.

Cognition enhancement by modafinil: a meta-analysis.

INTRODUCTION: Currently, there are a number of pharmaceuticals available that have potential to enhance cognitive functioning, some of which may ultimately be considered for such use in military operations. Some drugs with potential for cognition enhancement have already been studied for use in military operations specific to their primary effect in sleep regulation (i.e., dextroamphetamine, modafinil, caffeine). There is considerable information available on many of these drugs. However, considerations for military appropriateness must be based on proficient research (e.g., randomly controlled trial design). METHODS: A meta-analysis was conducted to summarize the current state of knowledge of these potentially cognition-enhancing drugs. The analysis only included studies which met inclusion criteria relevant to military research. RESULTS: The results of the literature review reveal a gap in research of the enhancement properties of the drugs of interest. The results yielded three studies (all of which studied modafinil) that met the criteria. The meta-analysis of these three studies revealed a relatively weak pooled effect of modafinil on some aspects of cognitive performance in normal, rested adults. DISCUSSION: While the results of this study support the efficacy of modafinil, the main finding is the large literature gap evaluating the short- and long-term effects of these drugs in healthy adults.

Modafinil as a replacement for dextroamphetamine for sustaining alertness in military helicopter pilots.

INTRODUCTION: Successful military aviation operations depend on maintaining continuous day-night operations. Stimulants are easy to use and popular for sustaining performance because their utility is not dependent upon environmental or scheduling modifications. Dextroamphetamine is authorized for use by the aircrews of all U.S. military services, but its potential for abuse and subsequent addiction is of aeromedical concern. Finding an alternative stimulant, such as modafinil, that displays a low affinity for dopamine uptake binding sites would prove extremely beneficial. This study sought to establish the efficacy and safety of modafinil during actual flying operations, thus providing the operational validity desired to approve the use of modafinil for helicopter flight operations. METHODS: During two, 40-h periods of sustained wakefulness, 18 helicopter pilots (17 men, 1 woman, mean years of age = 29.5) each completed 15 flights and other evaluations, during which they received 2 of 3 experimental conditions: 3 doses at 4-h intervals of modafinil (100 mg), dextroamphetamine (5 mg), or placebo. RESULTS: Statistical results showed that modafinil, like dextroamphetamine, maintained alertness, feelings of well-being, cognitive function, judgment, risk perception, and situation awareness of sleep-deprived aviators consistently better than placebo and without side effects of aeromedical concern. DISCUSSION: Like previous research, this study strongly suggests that both drugs can maintain acceptable levels of mood and performance during sleep deprivation. The results also confirm that modafinil is well tolerated and appears to be a good alternative to dextroamphetamine for countering the debilitating mood and cognitive effects of sleep loss during sustained operations.

Obstructive Sleep Apnea Among Army Aircrew.

INTRODUCTION: Obstructive sleep apnea (OSA) is a condition characterized by disrupted sleep and excessive daytime fatigue. Associated cognitive and psychomotor decrements pose a threat to aviators' performance and flight safety. Additionally, the longer term health effects associated with the disease can jeopardize an aviator's career and negatively impact operational outputs. This study reviews OSA prevalence, related comorbid conditions in Army aviators, and analyzes the aeromedical dispositions of affected individuals.METHODS: The U.S. Army Aeromedical Electronic Resource Office (AERO) database was interrogated for all cases of OSA from June 2005 through June 2015 using ICD-9 code 327.23. Prevalence rates for OSA and other comorbid conditions were then calculated using the total number of aviators in the AERO database.RESULTS: A total of 663 unique instances of OSA were found among the aviator population (N = 24,568), giving a point prevalence of 2.69%. Four cases affected women. Mean age of initial presentation was 42.62 yr and mean Body Mass Index was 28.69. The top five most prevalent comorbid conditions were hypertension, lumbago, degeneration of a lumbar or lumbosacral intervertebral disc, PTSD, and testicular hypofunction.DISCUSSION: Prevalence of OSA among aviators is lower than the general population but is not uncommon. A positive diagnosis requires a waiver or can result in suspension if not managed effectively, potentially leading to a reduction in aviator numbers. Aggressive health promotion and robust medical surveillance and aeromedical disposition management by the aeromedical community is essential to reduce OSA numbers, maintain aviator health, and maximize flight safety.Goldie C, Stork B, Bernhardt K, Gaydos SJ, Kelley AM. Obstructive sleep apnea among army aircrew. Aerosp Med Hum Perform. 2022; 93(5):415-420.

Trends in Metabolic Disorder in U.S. Army Aviators, 20162018.

INTRODUCTION: Recent epidemiological studies of U.S. Army aviators have suggested higher than anticipated rates of hyperlipidemia and metabolic disorder. The goal of this study was to determine whether this finding has persisted in 20162018 and to subsequently determine whether this trend is genuine and warrants further evaluation.METHODS: Data were requested from the U.S. Army Aeromedical Electronic Resource Office (AERO) and retrieved from the publicly available Defense Medical Surveillance System (DMSS) utilizing similar inclusion/exclusion criteria, where possible, as the earlier studies. For each year 20162018, incidence rates (per 1000 person years) for hyperlipidemia and metabolic syndrome were retrieved from DMSS, while percentages of aviators with these conditions were retrieved from AERO. The DMSS incidence rates were also age stratified. No formal analyses were conducted.RESULTS: Results from DMSS showed overall rates of hyperlipidemia ranging from 3.18 to 6.83 per 1000 person-years and for metabolic syndrome from 0.16 to 0.69 per 1000 person-years. The age stratified rates increased proportionally with age. AERO data showed a range of 0.81.5% of aviators had hyperlipidemia and for metabolic syndrome this ranged from 0.31 to 0.45%. These rates are broadly comparable to the previous studies findings.DISCUSSION: This studys findings suggest no continued increase in hyperlipidemia or metabolic disorder in aviators. While the exact cause is unknown, one could speculate a number of sources such as preferences in testing or encouragement from specific commanders or flight surgeons.Goldie C, McGhee J, Kelley AM. Trends in metabolic disorder in U.S. Army aviators, 20162018. Aerosp Med Hum Perform. 2021; 92(1):4346.

Aircrew Performance and Safety While Using Protective Masks in Response to Coronavirus Disease.

INTRODUCTION: In response to the urgent need for safe aircrew respiratory protection due to the COVID-19 pandemic, three small descriptive evaluations were conducted with aircrew and air traffic controllers (ATC) that assessed the impact of mask use on safety and performance onboard rotary wing aircraft.METHODS: A series of evaluations assessed aircrew performance using the 3MTM Model 1860 N95 respiratory protection mask, two aviation-specific cloth mask prototypes, and a commercial off-the-shelf aviation-specific cloth mask. The series of evaluations included different sets of subjects consisting of up to five Black Hawk helicopter aircrew members, air traffic control (ATC), and 12 CH-47 aircrew members. The Modified Rhyme Test was used to measure speech intelligibility and was administered in the UH-60 among crewmembers of the same aircraft, between pilots of different aircraft, and between the pilots and ATC. Measures of workload, usability, comfort, and pulse oximetry were also administered.RESULTS: Results from the Modified Rhyme Test indicated that all subjects scored greater than 80% accuracy given the proper microphone positioning relative to the mask. With respect to workload, NASA-TLX total scores for the perform radio communications task was 50.83.DISCUSSION: Despite an elevated perceived degree of workload on the communications flight task, results from the speech intelligibility test indicated that performance was maintained within the acceptable range as defined by MIL-STD-1474E, Design Criteria Standard Noise Limit. This abbreviated evaluation suggests that the face masks tested are safe for use by helicopter aircrew under the conditions tested.Cave KM, Kelley AM, Feltman KA, Gerstner JA, Stewart JL, Crowley JS. Aircrew performance and safety while using protective masks in response to coronavirus disease. Aerosp Med Hum Perform. 2021; 92(4):274280.

Selective Serotonin Reuptake Inhibitor Use Among Army Aviators.

INTRODUCTION: Mental health is an important aspect of Army aviation medicine given that it significantly impacts career longevity, readiness, and healthcare usage. One of the most commonly used classes of medications to treat mental health disorders is the selective serotonin reuptake inhibitor (SSRI). Here we present a descriptive epidemiological review of SSRI use in Army aviators over a 10-yr period.METHODS: An archival dataset retrieved from the U.S. Army Aeromedical Electronic Resource Office covering the years 2005 to 2015 was queried for cases of SSRI use. Frequencies were generated by primary diagnoses and aeromedical disposition for the SSRI subset of data.RESULTS: A total of 114 unique cases of SSRI use were identified (122 total aeromedical outcomes). These cases included 41 waiver recommendations, 59 suspension recommendations, and 22 cases of waiver continuations. The top five most common primary diagnoses were depressive disorder (N 32), anxiety state (N 21), posttraumatic stress disorder (N 16), single major depressive episode (N 13), and adjustment disorder with depressed mood (N 12).DISCUSSION: Understanding of the etiology, pathophysiology, and treatment of mental health disorders particularly within the safety-focused and unforgiving aviation environment has continued to evolve. With the application of evidence-based policy, deliberate aeromedical decision-making, and methodical risk mitigation, SSRI use does have a place within aviation. Aviators suffering in silence with deleterious impact to performance and safety or aircrew seeking services on the outside without knowledge or oversight of certification authorities must remain in the past.Kelley AM, Bernhardt K, McPherson M, Persson JL, Gaydos SJ. Selective serotonin reuptake inhibitor use among Army aviators. Aerosp Med Hum Perform. 2020; 91(11):897900.

Viability of tDCS in Military Environments for Performance Enhancement: A Systematic Review.

INTRODUCTION: Transcranial electrical stimulation (tES) as a method of cognitive enhancement in both diseased and healthy individuals has gained popularity. Its potential for enhancing cognition in healthy individuals has gained the interest of the military. However, before it being implemented into military training or operational settings, further work is needed to determine its efficacy and safety. Although a considerable amount of literature exists, few studies have specifically evaluated its use in enhancing cognition relative to operational, military tasks. Therefore, in a first step to evaluate its efficacy, we completed a systematic literature review of studies using transcranial direct current stimulation (tDCS), a type of tES, to enhance cognitive processes in healthy individuals. METHODS: A systematic literature review was conducted to identify literature published between 2008 and 2018 that used a method of tES for cognitive enhancement. As part of a larger literature review effort, 282 articles were initially retrieved. These were then screened to identify articles meeting predetermined criteria, to include those using various methods of tES, resulting in 44 articles. Next, the articles were screened for those using tDCS or high-definition tDCS, resulting in 34 articles for review and information extraction. RESULTS: Of the 34 articles reviewed, 28 reported some degree of enhancement (eg, improved accuracy on tasks and reduced reaction times). Areas of cognitive enhancements included executive functioning, creativity/cognitive flexibility, attention/perception, decision-making, memory, and working memory. However, the precise outcomes of enhancement varied given the range in tasks that were used to assess the constructs. Additionally, the stimulation parameters in terms of intensity applied, duration of stimulation, and brain region targeted for stimulation varied. CONCLUSIONS: The conclusions to be drawn from this systematic literature review include the identification of a brain region for targeting with stimulation to enhance a broad range of cognitive constructs applicable to military tasks, as well as stimulation parameters for duration and intensity. The dorsolateral prefrontal cortex was most frequently targeted in the studies that found enhanced performance across several cognitive constructs. Stimulation intensities of 2 mA and durations of 20 minutes or longer appeared frequently as well. Although several parameters were identified, further work is required before this type of technology can be recommended for operational use.

Probabilistically Valid Inference of Covariation From a Single x,y Observation When Univariate Characteristics Are Known.

Participants were asked to draw inferences about correlation from single x,y observations. In Experiment 1 statistically sophisticated participants were given the univariate characteristics of distributions of x and y and asked to infer whether a single x, y observation came from a correlated or an uncorrelated population. In Experiment 2, students with a variety of statistical backgrounds assigned posterior probabilities to five possible populations based on single x, y observations, again given knowledge of the univariate statistics. In Experiment 3, statistically naïve participants were given a problem analogous to that given in Experiment 1, framed verbally. Experiment 4 replicated Experiment 3 but added an "impossible to determine" response option. Models that rely on computing sample correlations make no predictions about these investigations. From a Bayesian perspective, participants' inferences in all four experiments tended to make probabilistically valid inferences as long as the single datum was directional. The results are discussed in light of the Brunswikian notion of vicarious functioning.

Simulator sickness in a helicopter flight training school.

INTRODUCTION: Simulator sickness (SS) is a common problem during flight training and can affect both instructor pilots (IP) and student pilots (SP). This study was conducted in response to complaints about a high incidence of SS associated with use of new simulators for rotary-wing aircraft. METHODS: The problem was evaluated using the Simulator Sickness Questionnaire (SSQ) to collect data on 73 IP and 129 SP who used the new simulators. Based on analysis of these data, operator comments, and a search of the literature, we recommended limiting simulator flights to 2 h, removing unusual or unnatural maneuvers, turning off the sidescreens to reduce the field-of-view, avoiding use of improperly calibrated simulators until repaired, and stressing proper rest and health discipline among the pilots. The success of these measures was evaluated 1 yr later by collecting SSQ data on 25 IP and 50 SP. RESULTS: There was a main effect of time, in that after the recommendations were implemented, there was a significant reduction in nausea, oculomotor, and total SSQ scores from the pre-study to the post-study. There was also a main effect of experience, as IP reported significantly greater SS than SP for the same scores. DISCUSSION: Implementation of the recommendations reduced SS in the new simulators at the cost of limiting session duration and shutting down some simulator features. Although the optimal solution to the SS problem lies in addressing SS during a simulator's design stage, these recommendations can be used as interim solutions to reduce SS.

Evaluation of the Military Functional Assessment Program for Return-to-Duty Decision Making: A Longitudinal Study.

Following concussion, return-to-duty decisions are made by medical providers and leaders using informal assessment, review of symptom resolution, and clinical assessments. In an effort to provide military-specific tasks for use in the decision making regarding return-to-duty, a battery developed from the set of basic soldier skills, the Military Functional Assessment Program (MFAP), was evaluated for construct validity using clinical assessment outcomes as well as the relationships between MFAP performance and indicators of long-term performance and satisfaction. A total of 48 participants were enrolled in the study providing baseline and post-treatment clinical assessment, and MFAP performance data. Twenty participants provided follow-up data at 6-month post-MFAP. Correlational analyses suggest significant relationships between MFAP performance ratings and clinical measures of vestibular and cognitive functions and psychological well-being. These findings are consistent with those from previous research on construct validity of the MFAP tasks. Performance on one MFAP task related to perceptions of performance and overall MFAP ratings related to satisfaction reported at 6 months. These findings provide preliminary, however limited, support for these tasks being indicative of the motivation and mental state of the program participant.