Kristin J. Heaton

Dynamic visuomotor synchronization: Quantification of predictive timing

When a moving target is tracked visually, spatial and temporal predictions are used to circumvent the neural delay required for the visuomotor processing. In particular, the internally generated predictions must be synchronized with the external stimulus during continuous tracking. We examined the utility of a circular visual-tracking paradigm for assessment of predictive timing, using normal human subjects. Disruptions of gaze–target synchronization were associated with anticipatory saccades that caused the gaze to be temporarily ahead of the target along the circular trajectory. These anticipatory saccades indicated preserved spatial prediction but suggested impaired predictive timing. We quantified gaze–target synchronization with several indices, whose distributions across subjects were such that instances of extremely poor performance were identifiable outside the margin of error determined by test–retest measures. Because predictive timing is an important element of attention functioning, the visual-tracking paradigm and dynamic synchronization indices described here may be useful for attention assessment.

Chemical sensitivity and chronic fatigue in Gulf War veterans : A brief report

The foci of this brief report are to (1) describe the prevalence of chemical sensitivity (CS) and chronic fatigue (CF) symptomatology and of presumptive multiple CS and CF syndrome diagnoses, and (2) explore the potential overlap between one purported case definition (ie, chronic multi-symptom illness) and these unexplained symptom syndromes in a well-characterized group of Gulf War veterans. The number of subjects with CS and CF symptomatology and presumptive multiple CS and CF syndrome diagnoses was higher in the Gulf War–deployed group compared with a group deployed to Germany during the Gulf War. However, the percent differences were not significant when comparing the presumptive diagnoses of multiple CS and CF syndrome. The characteristic differences between the groups and the overlap with chronic multi-symptom illness are also discussed.

Functional MRI approach to developmental methylmercury and polychlorinated biphenyl neurotoxicity.

Prenatal and early childhood exposure to methylmercury (MeHg) or polychlorinated biphenyls (PCBs) are associated with deficits in cognitive, sensory, motor and other functions measured by neurobehavioral tests. The main objective of this pilot study was to determine whether functional magnetic resonance imaging (fMRI) is effective for visualization of brain function alterations related to neurobehavior in subjects with high prenatal exposure to the two neurotoxicants, MeHg and PCBs. Twelve adolescents (all boys) from a Faroese birth cohort assembled in 1986-1987 were recruited based on their prenatal exposures to MeHg and PCB. All underwent fMRI scanning during behavioral tasks at age 15 years. Subjects with high mixed exposure to MeHg and PCBs were compared to those with low mixed exposure on fMRI photic stimulation and a motor task. Boys with low mixed exposures showed patterns of fMRI activation during visual and motor tasks that are typical of normal control subjects. However, those with high exposures showed activation in more areas of the brain and different and wider patterns of activation than the low mixed exposure group. The brain activation patterns observed in association with increased exposures to MeHg and PCBs are meaningful in regard to the known neurotoxicity of these substances. This methodology therefore has potential utility in visualizing structural neural system determinants of exposure-induced neurobehavioral dysfunction.

Predictive Visual Tracking: Specificity in Mild Traumatic Brain Injury and Sleep Deprivation

We tested whether reduced cognitive function associated with mild traumatic brain injury (mTBI) and sleep deprivation can be detected and distinguished using indices of predictive visual tracking. A circular visual tracking test was given to 13 patients with acute mTBI (recruited within 2 weeks of injury), 127 normal control subjects, and 43 healthy subjects who were fatigued by 26-hour sleep deprivation. Eye movement was monitored with video-oculography. In the mTBI-related portion of the study, visual tracking performance of acute mTBI patients was significantly worse than normal subjects (p < 0.001). In the sleep-deprivation-related portion of the study, no change was detected between the two baseline measures separated by 2 to 3 weeks, but the 26-hour sleep deprivation significantly degraded the visual tracking performance (p < 0.001). The mTBI subjects had substantially worse visual tracking than sleep-deprived subjects that could also be identified with different visual tracking indices, indicating possible different neurophysiological mechanisms. Results suggest that cognitive impairment associated with mTBI and fatigue may be triaged with the aid of visual tracking measures.

Attention and visual tracking degradation during acute sleep deprivation in a military sample

BACKGROUND Fatigue due to sleep restriction places individuals at elevated risk for accidents, degraded health, and impaired physical and mental performance. Early detection of fatigue-related performance decrements is an important component of injury prevention and can help to ensure optimal performance and mission readiness. This study used a predictive visual tracking task and a computer-based measure of attention to characterize fatigue-related attention decrements in healthy Army personnel during acute sleep deprivation. METHODS Serving as subjects in this laboratory-based study were 87 male and female service members between the ages of 18 and 50 with no history of brain injury with loss of consciousness, substance abuse, or significant psychiatric or neurologic diagnoses. Subjects underwent 26 h of sleep deprivation, during which eye movement measures from a continuous circular visual tracking task and attention measures (reaction time, accuracy) from the Attention Network Test (ANT) were collected at baseline, 20 h awake, and between 24 to 26 h awake. RESULTS Increases in the variability of gaze positional errors (46-47%), as well as reaction time-based ANT measures (9-65%), were observed across 26 h of sleep deprivation. Accuracy of ANT responses declined across this same period (11%). DISCUSSION Performance measures of predictive visual tracking accurately reflect impaired attention due to acute sleep deprivation and provide a promising approach for assessing readiness in personnel serving in diverse occupational areas, including flight and ground support crews.

Permethrin exposure from fabric-treated military uniforms under different wear-time scenarios.

The objective of the project was to ascertain whether urinary biomarkers of permethrin exposure are detected after wearing post-tailored, fabric-treated military uniforms under two different wear-time exposure scenarios. Study A occurred over 3.5 days and involved six participants wearing treated uniforms continuously for 30–32 h. Urine collection occurred at scheduled time points before, during, and after wearing the uniform. Study B, conducted over 19 days, included 11 participants wearing treated uniforms for 3 consecutive days, 8 h each day (with urine collection before, during, and after wear). Urinary biomarkers of permethrin (3-phenoxybenzoic acid (3PBA), cis- 2,2-(dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid (cDCCA), trans- 2,2-(dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid (tDCCA)) were detected during and after wear. Biomarker detection generally occurred over the 10- to 12-h period after putting on the uniform and subsided 24 h following uniform removal (in both Study A and B scenarios). Those wearing permethrin-treated uniforms under the longer wear-time scenario (Study A) excreted significantly higher cumulative mean levels compared with those in Study B (3.29 times higher for 3PBA and 2.23 times higher for the sum of c/tDCCA (P≤0.001)). Findings suggest that wearing permethrin-treated clothing does increase absorbed, internal dose levels of permethrin above population levels and is significantly related to wear-time duration.

The Occupational JP8 Exposure Neuroepidemiology Study (OJENES): repeated workday exposure and central nervous system functioning among US Air Force personnel.

One of the most prevalent workplace chemical exposures historically and currently confronting the global military and civilian workforce is jet propellant (JP) fuel (e.g., JP4, JP5, JP8, jet A1), a complex mixture of numerous hydrocarbon compounds and additives. To date, numerous protective and preventive strategies (e.g., federal exposure limits, workplace procedure protocols, protective gear such as goggles, respirator use, gloves, and coveralls) have been put in place to minimize acutely toxic exposure levels. However, questions remain regarding the effect of repeated exposures at lower (than regulated) levels of JP fuel. The Occupational JP8 Exposure Neuroepidemiology Study (OJENES) was designed to examine the relationships between occupational JP8 exposure over multiple, repeated workdays and specific aspects of central nervous system (CNS) functioning among Air Force (AF) personnel. In this report, we present the OJENES methodology, descriptive findings related to participant characteristics, JP8 exposure levels observed over a work week among higher and lower exposure groups, and neuropsychological task performances at the first study assessment. Results indicated minimal differences between participants in the high and lower exposure groups in terms of descriptive characteristics, other than daily JP8 exposure levels (p<0.001). In addition, neuropsychological task performances for most task measures were not found to be significantly different from reported reference ranges. These findings demonstrated that confounding and misclassification of exposure and outcome status are not major concerns for the study. Therefore, future OJENES analyses targeting the more focused research questions regarding associations between JP8 exposure and CNS functioning are likely to provide valid conclusions, as they will be less influenced by these research biases.

Postural sway and exposure to jet propulsion fuel 8 among US Air Force personnel.

Objective: To determine whether short-term jet propulsion fuel 8 (JP-8) exposure is associated with balance measurements in JP-8–exposed air force personnel. Methods: As part of a larger neuroepidemiology study, balance tasks were completed by JP-8–exposed individuals (n = 37). Short-term JP-8 exposure was measured using personal breathing zone levels and urinary biomarkers. Multivariate linear regression analyses were conducted to examine the relationship between workday JP-8 exposure and postural sway. Results: Balance control decreased as the task became more challenging. Workday exposure to JP-8, measured by either personal air or urinary metabolite levels, was not significantly related to postural sway. Increases in workday postural sway were associated with demographic variables, including younger age, being a current smoker, and higher body mass index. Conclusion: Results suggest that short-term workday JP-8 exposure does not significantly contribute to diminished balance control.

Psychological and Physical Characteristics of U.S. Marine Recruits

This study examined psychological and physical health factors in a cohort of U.S. Marine recruits with the goal of developing a comprehensive understanding of attributes recruits bring to training. 1,350 male recruits completed a multimeasure survey during the first week of training. A 2-way multivariate analysis of variance (MANOVA) was conducted to explore the relationship of hardiness dimensions on several psychological and physical factors. Compared with other military samples, this cohort reported similar levels on hardiness control and rigidity subscales. Recruits who reported higher scores on a measure of positive hardiness also reported higher scores on measures of grit, grit ambition, sensation seeking, training expectations, positive ways of coping, physical and mental health, fitness scores, and lower scores on a measure of depression. This study provides a more complete understanding of the complex array of attributes of Marine recruits and forms a foundation for predictive models of injury risk and/or attrition.

A retrospective study of anxiety disorder diagnoses in the military from 2000 to 2009.

The objective of this study was to describe trends in the diagnostic rates for anxiety disorders (ADs) types in the U.S. military from 2000 to 2009. Data for the numbers of diagnosed cases for the first documented occurrence of ADs during ambulatory visits while serving in the military were obtained from the Defense Medical Epidemiology Database for all active duty service members and examined across branch of service and by gender. Results indicate that Anxiety Not Otherwise Specified (ANOS) was the most frequently diagnosed AD type in each of the 10 years between 2000 and 2009, with an average rate of 0.8 per 100 service members for first service occurrence, followed by PTSD at a rate of 0.5 out of every 100. Starting in 2002, the yearly first occurrence rates of ANOS and PTSD were significantly higher (p<0.001) compared to each proceeding year, with the same pattern present among males and females separately. The majority of first occurrence AD diagnoses were diagnosed in the Army (47% of Anxiety NOS and 60% of PTSD cases) compared to the other service branches (i.e., Navy, Air Force, and Marines).