Dennis L. Reeves

Effect of repeated exposures to cold on cognitive performance in humans.

The effects of repeated exposure to cold temperature on cognitive performance were examined in 10 male subjects who were exposed to control (25 degrees C) and cold (10 degrees C) conditions on 10 successive days. A cognitive test battery (ANAM-ICE) was administered each day to assess complex and simple cognitive functioning accuracy, efficiency and response time. Rectal (T(rect)) and skin temperatures, thermal sensations, metabolic rate (M) and cardiovascular reactivity were also recorded. With the used cold exposure, inducing cold sensations and discomfort, superficial skin cooling (6-7 degrees C) and a slightly lowered T(rect) (0.4 degrees C) we observed three distinct patterns of cognitive performance: 1) negative, reflected in increased response times and decreased accuracy and efficiency; 2) positive, reflected in decreased response time and increased efficiency; and 3) mixed, reflected in a pattern of increases in both accuracy and response time and decreases in efficiency, and a pattern of decreases in both accuracy and response time. T(rect), thermal sensations, diastolic blood pressure (DBP) and heart rate (HR) were independent predictors of decreased accuracy, but also decreased response time. Cognitive performance efficiency was significantly improved and response times shorter over the 10-d period both under control and cold exposures suggesting a learning effect. However, the changes in cognitive performance over the 10-d period did not differ markedly between control and cold, indicating that the changes in the thermal responses did not improve performance. The results suggest that cold affects cognitive performance negatively through the mechanisms of distraction and both positively and negatively through the mechanism of arousal.

Neuropsychological test performance in soldiers with blast-related mild TBI.

This exploratory study was conducted to increase understanding of neuropsychological test performance in those with blast-related mild traumatic brain injury (mTBI). The two variables of interest for their impact on test performance were presence of mTBI symptoms and history of posttraumatic stress disorder (PTSD). Forty-five soldiers postblast mTBI, 27 with enduring mTBI symptoms and 18 without, completed a series of neuropsychological tests. Seventeen of the 45 met criteria for PTSD. The Paced Auditory Serial Addition Test (Frencham, Fox, & Mayberry, 2005; Spreen & Strauss, 1998) was the primary outcome measure. Two-sided, 2-sample t tests were used to compare scores between groups of interest. Presence of mTBI symptoms did not impact test performance. In addition, no significant differences between soldiers with and without PTSD were identified. Standard neuropsychological assessment may not increase understanding about impairment associated with mTBI symptoms. Further research in this area is indicated.

Predictors of adherence to triptans: factors of sustained vs lapsed users.

Objective.— The present study was conducted to identify factors that predict adherence to triptans by migraine patients.

Interpersonal Touch in High School Relative to Sex and Race

Previous studies have indicated that interpersonal touch decreases from kindergarten through junior high. In the present study 1154 pairs of high school students were observed in school cafeteria queues. Instances of touch were recorded along with body parts used to touch and touched. High school students were observed to segregate themselves by race and sex as did the primary and junior high students in the earlier studies. Touch was not less probable than that observed in younger students. Cross-sex touch was not more frequent as had been predicted. Touch was highest among black students. An increase in aggressive touch seen in female junior high students was not observed in the present study.

The Development of Personal Space in Primary School Children

Personal space in school cafeteria queues was observed for 1,047 children in kindergarten through sixth grade in seven public schools. It was found that children segregate themselves both racially and sexually in the queues. In three of the schools that were racially mixed, the children stood closer in the lower grades than in the higher grades, they stood closer to same-sex children than to other-sex children, but there was no racial difference. In three of the schools where all of the children were white, there was an increase in personal space across grades for all sex combinations except male to male. In two of the schools where all of the children were black, there was no significant increase in personal space across grades. The children in the white schools had greater queue distances than children in the black schools throughout the upper grades. In general, the results were similar to those obtained in other studies involving observation in natural settings and different from results obtained using simulated interaction.

Uncovering Latent Deficits Due to Mild Traumatic Brain Injury by Using Normobaric Hypoxia Stress

Memory deficits and other cognitive symptoms frequently associated with mTBI are commonly thought to resolve within 7–10 days. This generalization is based principally on observations made in individuals who are in the unstressed environmental conditions typical of a clinic and so does not consider the impact of physiologic, environmental, or psychological stress. Normobaric hypoxic stress can be generated with normal mean sea level (MSL) air, which is about 21% oxygen (O2) and 78% nitrogen (N), by reducing the percentage of O2 and increasing the percentage of N so that the resultant mixed-gas has a partial pressure of O2 approximating that of specified altitudes. This technique was used to generate normobaric hypoxic equivalents of 8,000, 12,000, and 14,000 feet above MSL in a group of 36 volunteers with a mTBI history and an equal number of controls matched on the basis of age, gender, tobacco smoking consumption, weight, height, and body mass index. Short-term visual memory was tested using the Matching to Sample (M2S) subtest of the BrainCheckers analog of the Automated Neuropsychological Assessment Metrics. Although there were no significant differences in M2S performance between the two groups of subjects at MSL, with increased altitude, the mTBI group performance was significantly worse than that of the control group. When the subjects were returned to MSL, the difference disappeared. This finding suggests that the “hypoxic challenge” paradigm developed here has potential clinical utility for assessing the effects of mTBI in individuals who appear asymptomatic under normal conditions.

Psychoneuroendocrine effects of combined thyroxine and triiodothyronine versus tyrosine during prolonged Antarctic residence

Objectives. We previously reported that cognitive function improves with thyroxine and that there is a circannual pattern to mood and human TSH during Antarctic residence. To extend these findings, we examined the effects of tyrosine and a combined levothyroxine/liothyronine supplement in euthyroid men and women who spent the austral summer (n = 43) and/or winter (n = 42) in Antarctica. Study Design. Randomized, placebo-controlled, clinical trial. Methods. Subjects were randomized to receive the following each day for 91.6 +/- 3.2 days in summer and/or 138.0 +/- 3.2 days in winter: (1) 12g tyrosine mixed in 113g applesauce; (2) 50 microg of levothyroxine and 12.5 microg of liothyronine (T4-T3 Supplement); or (3) placebo. Cognitive performance and mood were assessed using the Automatic Neuropsychological Assessment Metric - Isolated and Confined Environments. Results. With placebo in summer, mood did not change while TSH decreased by 28%; in winter, there was a 136% degradation in mood (p & 0.01) and TSH increased by 18%. With combined T4-T3 supplement, there was a 51% degradation in mood in summer compared with placebo (p & 0.05) and TSH decreased by 57%; in winter there was a 135% degradation in mood while TSH was reduced by 26% (p & 0.05). Tyrosine use in summer was associated with no change in mood and a 30% decline in TSH, while in winter there was a 47% improvement in mood and TSH decreased by 28% along with a 6% increase in fT3 (p & 0.05). Conclusions. Administration of tyrosine leads to a significant reduction in serum TSH and improvement in mood in winter compared with placebo, while the combined T4-T3 supplement leads to a worsening of mood in summer and no improvement in winter. There appears to be a seasonal influence on the psychological response to interventions and the relationship to changes in TSH reductions.

A randomized placebo-controlled clinical trial of the effectiveness of thyroxine and triiodothyronine and short-term exposure to bright light in prevention of decrements in cognitive performance and mood during prolonged Antarctic residence

Objective  We examined the effects of a combined levothyroxine/liothyronine supplement and exposure to bright (10,000 lux) light in euthyroid men and women who spent the austral summer (n = 43) and/or winter (n = 42) in Antarctica.

Endogenous hyperthermia in normal human subjects. I: Experimental study of evoked potentials and reaction time

Previous work on awake guinea pigs and rats in the authors’ laboratory revealed that microwave-induced elevations of brain temperature (ΔTs from 1° to 3° C over resting baselines) are associated with reliable reductions in latencies of flash-evoked brain potentials’ (EPs). To assess the generality of this finding in the normal human being, and to avoid the ethical problem of whole-body human exposure to an intense microwave field, ΔTs were induced endogenously by vigorous exercise and by insulative and vapor-barrier clothing. Twenty male athletes, 18 to 22 years of age, were randomly but equally divided into counterbalanced experimental and control groups for a single 3-h morning or afternoon session of measurements. During baseline measures, EPs of three types were observed: flash-evoked N1, pattern-reversal P100, and event-related P300. In addition, simple reaction times (RTs) to photic stimulation were recorded. All measures were repeated after sham warming of the 10 control subjects and after tympanically indexed brain temperatures of the 10 experimental subjects were elevated by an average of 1.2° C above control values. EP and RT latencies were reliably reduced in association with the ΔTs, the mean reductions ranging from 3% to 9%. The data on the human flash-evoked N1 component compare favorably with data recorded from rats and guinea pigs that have undergone exogenous elevations of temperature by microwave irradiation. The data on RTs and other EP components are consistent with the thesis that human CNS activity in general is accelerated during a modest bout of whole-body hyperthermia.

Enhancement of discrimination learning following unilateral lesions of posterior neocortex in guinea pigs

Abstract Monocular acquisition and interocular transfer of a horizontal-vertical discrimination were measured in 16 male albino guinea pigs which were restricted to using either the contralateral or ipsilateral primary visual fibers; restriction was accomplished by introduction of a unilateral striate lesion coupled with monocular occlusion. Eight sham-operated animals served as controls. The animals restricted to use of the contralateral fibers showed reliably enhanced rates of acquisition as compared to the controls, while the animals restricted to the ipsilateral fibers were unable to master the discrimination. The control animals learned readily, but demonstrated fairly low levels of interocular transfer. The data suggest that there is some form of interhemispheric interference which is eliminated by the introduction of unilateral ablations of the posterior neocortex.