The use of dose equivalency as a risk assessment index in behavioral neurotoxicology

Detecting impairment: sensitive cognitive measures of dose-related acute alcohol intoxication

The cognitive impairment that results from acute alcohol intoxication is associated with considerable safety risks. Other psychoactive substances, such as medications, pose a similar risk to road and workplace safety. However, there is currently no legal limit for operating vehicles or working while experiencing drug-related impairment. The current study sought to identify a brief cognitive task sensitive to a meaningful degree of impairment from acute alcohol intoxication to potentially stand as a reference from which to quantify impairment from other similar substances. A placebo-controlled single-blind crossover design was employed to determine the relative sensitivity of four commonly-administered cognitive tasks (Compensatory Tracking Task, Digit Symbol Substitution Test, Brief Stop Signal Task and Inspection Time Task) to alcohol-related impairment in male social drinkers at ~0.05% ascending breath alcohol concentration (BrAC), ~0.08% peak BrAC and 0.05% descending BrAC. The Inspection Time Task was identified as the most sensitive task, detecting a medium to large magnitude increase in impairment (g ≈ 0.60) at 0.05% ascending and descending BrAC, and a large magnitude effect size (g = 0.80) at 0.08% peak BrAC. The remaining tasks failed to demonstrate sensitivity to dose-dependent and limb-dependent changes in alcohol-induced impairment. The Inspection Time Task was deemed the most sensitive task for screening alcohol-related impairment based on the present results. Confirmation of equivalence with other drug-related impairment and sensitivity to alcohol-induced impairment in real-world settings should be established in future research.

Functional biomarkers for the acute effects of alcohol on the central nervous system in healthy volunteers

The central nervous system (CNS) effects of acute alcohol administration have been frequently assessed. Such studies often use a wide range of methods to study each of these effects. Unfortunately, the sensitivity of these tests has not completely been ascertained. A literature search was performed to recognize the most useful tests (or biomarkers) for identifying the acute CNS effects of alcohol in healthy volunteers. All tests were grouped in clusters and functional domains. Afterwards, the effect of alcohol administration on these tests was scored as improvement, impairment or as no effect. Furthermore, dose-response relationships were established. A total number of 218 studies, describing 342 different tests (or test variants) were evaluated. Alcohol affected a wide range of CNS domains. Divided attention, focused attention, visuo-motor control and scales of feeling high and of subjective drug effects were identified as the most sensitive functional biomarkers for the acute CNS effects of alcohol. The large number of CNS tests that are used to determine the effects of alcohol interferes with the identification of the most sensitive ones and of drug-response relationships. Our results may be helpful in selecting rational biomarkers for studies investigating the acute CNS effects of alcohol or for future alcohol- interaction studies.

The challenge of uncoupled motion: duration of cognitive and physiological aftereffects

OBJECTIVE

This study aimed to document the cognitive aftereffects of exposure to uncoupled motion and the time course of recovery from these aftereffects.

BACKGROUND

Uncoupled motion refers to a situation in which an individual is simultaneously exposed to two asynchronous motions, either real or virtual. These environments are a challenge for designers because technology that is supposed to increase the user's task performance may actually lead to decreased task performance.

METHOD

In the study, 11 male participants, (median age =32 years) with prior flight experience (median=600 hr) were exposed to an uncoupled motion environment consisting of a flight simulator on a vertically oscillating platform. Participants completed a cognitive test battery, a balance test, and a dynamic visual acuity test preexposure, immediately postexposure, and 2, 4, 6, 8, and 24 hr postexposure.

RESULTS

The uncoupled motion scenario led to significant cognitive aftereffects that cannot be solely attributed to motion sickness. These aftereffects lasted between 2 and 4 hr postexposure. The scenario generated some physiological aftereffects that lasted between 1 and 2 hr postexposure. However, it is likely that these aftereffects can be attributed to motion sickness.

CONCLUSION

Uncoupled motion can cause unappreciated effects, such as degraded cognitive performance.

APPLICATION

System designs that create uncoupled motion need to be evaluated for the potential to generate operator impairment, and designs should be modified to minimize this potential wherever possible. When redesign is not possible, system-use guidelines should be developed to minimize impairment. The current results suggest operators avoid performing cognitively demanding tasks for at least 2 hr postexposure.

Quantitative Comparisons of the Acute Neurotoxicity of Toluene in Rats and Humans

The behavioral and neurophysiological effects of acute exposure to toluene are the most thoroughly explored of all the hydrocarbon solvents. Behavioral effects have been experimentally studied in humans and other species, for example, rats. The existence of both rat and human dosimetric data offers the opportunity to quantitatively compare the relative sensitivity to acute toluene exposure. The purpose of this study was to fit dose-effect curves to existing data and to estimate the dose-equivalence equation (DEE) between rats and humans. The DEE gives the doses that produce the same magnitude of effect in the two species. Doses were brain concentrations of toluene estimated from physiologically based pharmacokinetic models. Human experiments measuring toluene effects on choice reaction time (CRT) were meta-analyzed. Rat studies employed various dependent variables: amplitude of visual-evoked potentials (VEPs), signal detection (SIGDET) accuracy (ACCU) and reaction time (RT), and escape-avoidance (ES-AV) behaviors. Comparison of dose-effect functions showed that human and rat sensitivity was practically the same for those two task regimens that exerted the least control over the behaviors being measured (VEP in rats and CRT in humans) and the sensitivity was progressively lower for SIGDET RT, SIGDET ACCU, and ES-AV behaviors in rats. These results suggested that the sensitivity to impairment by toluene depends on the strength of control over the measured behavior rather than on the species being tested. This interpretation suggests that (1) sensitivity to toluene would be equivalent in humans and rats if both species performed behaviors that were controlled to the same extent, (2) the most sensitive tests of neurobehavioral effects would be those in which least control is exerted on the behavior being measured, and (3) effects of toluene in humans may be estimated using the DEEs from rat studies despite differences in the amount of control exerted by the experimental regimen or differences in the behaviors under investigation.

Toward cost-benefit analysis of acute behavioral effects of toluene in humans

There is increasing interest in being able to express the consequences of exposure to potentially toxic compounds in monetary terms in order to evaluate potential cost-benefit relationships of controlling exposure. Behavioral effects of acute toluene exposure could be subjected to cost-benefit analysis if the effects of toluene were quantitatively compared to those of ethanol ingestion, which has been monetized for applied contexts. Behavioral effects of toluene and ethanol were quantified by meta-analysis of studies from the peer-reviewed literature describing their effects on choice reaction time (reaction time in a test requiring a subject to choose among two or more alternatives before responding). The internal doses of these compounds were estimated by a general physiological and toxicokinetic (GPAT) simulation from exposure parameters provided in the reports. The reported effects were converted to a common metric (proportion of baseline) and related to the estimated internal doses of toluene and ethanol, from which dose-effect equations were fitted. The estimated effect of toluene was compared to the estimated effect of ethanol on the same dependent variable by deriving a dose-equivalence equation (DEE) to express the dose of toluene as an equivalent dose of ethanol on the basis of equal effect magnitude. A nomogram was constructed by GPAT simulation to relate the environmental exposure concentration of toluene to the equivalent effect magnitude of a range of ethanol internal doses. Behavioral effects and their evaluation are determined by internal doses, which in turn are determined by a variety of variables. In addition to concentration and duration of exposure, which determine internal dose by pharmacokinetic processes, the activity level of exposed persons is a major factor. This analysis provides a continuous function of the consequences of toluene exposure expressed as ethanol-equivalent doses within confidence limits. The resulting function has the potential to estimate the monetary values of behavioral deficits caused by a range of exposures to toluene from existing monetized information on ethanol.

Neuromotor Effects of Acute Ethanol Inhalation Exposure in Humans: A Preliminary Study

Ethanol (ETOH) is added to unleaded gasoline to decrease environmental levels of carbon monoxide from automobiles emissions. Therefore, addition of ETOH in reformulated fuel will most likely increase and the involuntarily human exposure to this chemical will also increase. This preliminary study was undertaken to evaluate the possible neuromotor effects resulting from acute ETOH exposure by inhalation in humans. Five healthy non-smoking adult males, with no history of alcohol abuse, were exposed by inhalation, in a dynamic, controlled-environment exposure chamber, to various concentrations of ETOH (0, 250, 500 and 1,000 ppm in air) for six hours. Reaction time, body sway, hand tremor and rapid alternating movements were measured before and after each exposure session by using the CATSYS 7.0 system and a diadochokinesimeter. The concentrations of ETOH in blood and in alveolar air were also measured. ETOH was not detected in blood nor in alveolar air when volunteers were exposed to 250 and 500 ppm, but at the end of exposure to 1,000 ppm, blood and alveolar air concentrations were 0.443 mg/100ml and 253.1 ppm, respectively. The neuromotor tests did not show conclusively significant differences between the exposed and non-exposed conditions. In conclusion, this study suggests that acute exposure to ethanol at 1,000 ppm or lower or to concentrations that could be encountered upon refueling is not likely to cause any significant neuromotor alterations in healthy males.

Cybersickness in the presence of scene rotational movements along different axes

Compelling scene movements in a virtual reality (VR) system can cause symptoms of motion sickness (i.e., cybersickness). A within-subject experiment has been conducted to investigate the effects of scene oscillations along different axes on the level of cybersickness. Sixteen male participants were exposed to four 20-min VR simulation sessions. The four sessions used the same virtual environment but with scene oscillations along different axes, i.e., pitch, yaw, roll, or no oscillation (speed: 30 degrees/s, range: +/- 60 degrees). Verbal ratings of the level of nausea were taken at 5-min intervals during the sessions and sickness symptoms were also measured before and after the sessions using the Simulator Sickness Questionnaire (SSQ). In the presence of scene oscillation, both nausea ratings and SSQ scores increased at significantly higher rates than with no oscillation. While individual participants exhibited different susceptibilities to nausea associated with VR simulation containing scene oscillations along different rotational axes, the overall effects of axis among our group of 16 randomly selected participants were not significant. The main effects of, and interactions among, scene oscillation, duration, and participants are discussed in the paper.

Applying quality control charts to the analysis of single-subject data sequences

Techniques from the field of quality control can be used to classify the quality of individual samples of physical or cognitive performance. After stable baselines have been established for an individual, deviations in performance can be evaluated using control charts. The effectiveness of this approach in evaluating cognitive performance was tested using databases collected under a variety of risk factors. The sensitivity and specificity characteristics of Shewhart, cumulative-sum (CUSUM), and exponentially weighted moving average (EWMA) control charts were determined for a total of 174 trials involving 10 participants and 23 cognitive performance assessment measures. The most effective technique in each case was typically a function of the specific performance measure and the type of performance change being evaluated. Sensitivity and specificity for the best techniques were as high as 100%. This study demonstrated the usefulness of quality control charts as a tool to evaluate individual participant performance over time. Actual or potential applications of this research include readiness-to-perform screening of industrial workers in order to improve the health and safety of the workforce.

A PC-based software test for measuring alcohol and drug effects in human subjects

A new software-based visual search and divided-attention test of cognitive performance was developed and evaluated in an alcohol dose-response study with 24 human subjects aged 21-62 years. The test used language-free, color, graphic displays to represent the visuospatial demands of driving. Cognitive demands were increased over previous hardware-based tests, and the motor skills required for the test involved minimal eye movements and eye-hand coordination. Repeated performance on the test was evaluated with a latin-square design by using a placebo and two alcohol doses, low (0.48 g/kg/LBM) and moderate (0.72 g/kg/LBM). The data on 7 females and 17 males yielded significant falling and rising impairment effects coincident with moderate rising and falling breath alcohol levels (mean peak BrALs = 0.045 g/dl and 0.079 g/dl). None of the subjects reported eye-strain or psychomotor fatigue as compared with previous tests. The high sensitivity/variance relative to use in basic and applied research, and worksite fitness-for-duty testing, was discussed. The most distinct advantage of a software-based test that operates on readily available PCs is that it can be widely distributed to researchers with a common reference to compare a variety of alcohol and drug effects.