Biomedical subjects

Harris R Lieberman

Publications and source records attributed to Harris R Lieberman.

7 recordsLinked to original sources

PubMed2003

Nutrition, brain function and cognitive performance.

Military interest in the effects of nutritional factors on cognitive function has stimulated considerable research on a variety of food constituents. This paper will review the research on the amino acids tryptophan and tyrosine, caffeine and carbohydrate. It will focus on research that addresses the potential utility of these compounds in military applications, particularly the acute, as opposed to chronic, effects of these substances on cognitive functions such as alertness, vigilance and resistance to stress. Caffeine, the most intensively studied food constituent, has unequivocal beneficial effects on vigilance, and in sleep deprived individuals it enhances other cognitive functions as well. Tryptophan, although it clearly has sedative-like properties, has not been extensively studied by military laboratories for use as a hypnotic, due to safety concerns. Tyrosine has been examined in animal models and human studies, and appears to prevent the substantial decline in various aspects of cognitive performance and mood associated with many kinds of acute stress. Carbohydrate supplementation appears to enhance cognitive performance in soldiers engaged in sustained, intense physical activities that expend high levels of energy.

Adult↗

PubMed2003

A comparison of tyrosine against placebo, phentermine, caffeine, and D-amphetamine during sleep deprivation.

Sleep deprivation can impair alertness and cognitive and motor performance. We hypothesized that the amino acid tyrosine might reduce deleterious effects of sleep deprivation. Seventy-six healthy males, age 18-35 years, participated in a four-day protocol that included a habituation night, a baseline night, a 40.5 h period without sleep, and a recovery night. Tyrosine 150 mg/kg, caffeine 300 mg/70 kg, phentermine 37.5 mg, D-amphetamine 20 mg and placebo were administered in a double-blind, randomized fashion to compare their effects on the time it took to fall asleep, on endocrine responses during sleep deprivation, and on sleep quantity, quality and architecture as measured by polysomnography during recovery sleep. When given after 36 h without sleep, tyrosine had no significant effect on any parameter of sleep. D-amphetamine produced marked decrease in sleep drive but caused deleterious effects on many aspects of recovery sleep. Still, D-amphetamine was associated with increased alertness on the first recovery day. Phentermine and caffeine both decreased sleep drive during sleep deprivation, but phentermine impaired rapid-eye-movement (REM) recovery sleep. Tyrosine (when compared to placebo) had no effect on any sleep related measure, but it did stimulate prolactin release.

Adolescent↗

PubMed2003

Effects of tyrosine, phentermine, caffeine D-amphetamine, and placebo on cognitive and motor performance deficits during sleep deprivation.

Cognitive and motor performance are critical in many circumstances and are impaired by sleep deprivation. We administered placebo, tyrosine 150 mg/kg, caffeine 300 mg/70 kg, phentermine 37.5 mg and D-amphetamine 20 mg at 15.30 h following overnight sleep deprivation and compare their effects on cognitive and motor performance in healthy young men. Tests of visual scanning, running memory, logical reasoning, mathematical processing, the Stroop task, four-choice serial reaction time, time wall take, pursuit tracking, visual vigilance, Trails (B) task and long-term memory were evaluated at standardized intervals before, during and after sleep deprivation and drugs. Performance decrements with sleep deprivation occurred in visual scanning, running memory, logical reasoning, mathematical processing, the Stroop test, the time wall test, tracking and visual vigilance. Interestingly, with sleep deprivation some tests improved and others did not deteriorate. Improvements with medication following sleep deprivation were seen in running memory, logical reasoning, mathematical processing, tracking and visual vigilance. Although less effective than D-amphetamine, tyrosine improved performance on several tests. We conclude that all drugs tested improved at least some aspects of cognitive and motor performance after sleep deprivation. As a naturally occurring amino acid, and thus amenable to nutritional strategies, tyrosine may deserve further testing.

Adolescent↗

PubMed2003

Caffeine effects on marksmanship during high-stress military training with 72 hour sleep deprivation.

PURPOSE: Navy SEALs (sea, air, land) are elite special warfare units that conduct unconventional warfare primarily in marine environments. Marksmanship accuracy and sighting time were quantified with 62 male trainees during Navy SEAL Hell Week, which involves the combined stress of sleep loss, operational combat scenarios, and cold-wet environmental conditions. Caffeine was administered to minimize deficits due to sleep deprivation. METHODS: Volunteers dry-fired a disabled rifle equipped with a laser-based marksmanship simulator system to measure shooting speed and accuracy. The target was a 2.3-cm diameter circle at a distance of 5 m, simulating a 46 cm target at a distance of 50 m. Marksmanship was assessed prior to training, and at 73 and 80 h into Hell Week. Volunteers were randomly assigned to 1 of 4 treatments: 100, 200, or 300 mg of caffeine or a placebo. Dosing occurred 72 h after training commenced. RESULTS: The combined effects of almost 73 h of total sleep deprivation and operational and environmental stress degraded all marksmanship accuracy measures (p < 0.05) as shown by the 37.5% increase in percent of targets missed, 38% increase in distance from center of mass of the target, and the 235% increase in shot group tightness. Sighting time increased by 53% or 3.1 s after 73 h of sleep deprivation (p < 0.05). Sighting time was significantly faster in sleep deprived individuals after taking 200 or 300 mg of caffeine compared with placebo or 100 mg of caffeine. No differences in accuracy measures between caffeine treatment groups were evident at any test period. CONCLUSION: During periods of sleep deprivation combined with other stressors, the use of 200 or 300 mg of caffeine enabled SEAL trainees to sight the target and pull the trigger faster without compromising shooting accuracy.

Adult↗

PubMed2002

Effects of caffeine, sleep loss, and stress on cognitive performance and mood during U.S. Navy SEAL training. Sea-Air-Land.

RATIONALE: When humans are acutely exposed to multiple stressors, cognitive performance is substantially degraded. Few practical strategies are available to sustain performance under such conditions. OBJECTIVE: This study examined whether moderate doses of caffeine would reduce adverse effects of sleep deprivation and exposure to severe environmental and operational stress on cognitive performance. METHODS: Volunteers were 68 U.S. Navy Sea-Air-Land (SEAL) trainees, randomly assigned to receive either 100, 200, or 300 mg caffeine or placebo in capsule form after 72 h of sleep deprivation and continuous exposure to other stressors. Cognitive tests administered included scanning visual vigilance, four-choice visual reaction time, a matching-to-sample working memory task and a repeated acquisition test of motor learning and memory. Mood state, marksmanship, and saliva caffeine were also assessed. Testing was conducted 1 and 8 h after treatment. RESULTS: Sleep deprivation and environmental stress adversely affected performance and mood. Caffeine, in a dose-dependent manner, mitigated many adverse effects of exposure to multiple stressors. Caffeine (200 and 300 mg) significantly improved visual vigilance, choice reaction time, repeated acquisition, self-reported fatigue and sleepiness with the greatest effects on tests of vigilance, reaction time, and alertness. Marksmanship, a task that requires fine motor coordination and steadiness, was not affected by caffeine. The greatest effects of caffeine were present 1 h post-administration, but significant effects persisted for 8 h. CONCLUSIONS: Even in the most adverse circumstances, moderate doses of caffeine can improve cognitive function, including vigilance, learning, memory, and mood state. When cognitive performance is critical and must be maintained during exposure to severe stress, administration of caffeine may provide a significant advantage. A dose of 200 mg appears to be optimal under such conditions.

Adult↗

PubMed2002

Carbohydrate administration during a day of sustained aerobic activity improves vigilance, as assessed by a novel ambulatory monitoring device, and mood.

BACKGROUND: The brain requires a continuous supply of glucose to function adequately. During aerobic exercise, peripheral glucose requirements increase and carbohydrate supplementation improves physical performance. The brain's utilization of glucose also increases during aerobic exercise. However, the effects of energy supplementation on cognitive function during sustained aerobic exercise are not well characterized. OBJECTIVE: The effects of energy supplementation, as liquid carbohydrate, on cognitive function during sustained aerobic activity were examined. DESIGN: A double-blind, placebo-controlled, between-subjects design was used. Young, healthy men (n = 143) were randomly assigned to 1 of 3 treatment groups. The groups received either a 6% (by vol) carbohydrate (35.1 kJ/kg), 12% (by vol) carbohydrate (70.2 kJ/kg), or placebo beverage in 6 isovolumic doses, and all groups consumed 2 meals (3200 kJ). Over the 10-h study, the subjects performed physically demanding tasks, including a 19.3-km road march and two 4.8-km runs, interspersed with rest and other activities. Wrist-worn vigilance monitors, which emitted auditory stimuli (20/h) to which the subjects responded as rapidly as possible, and a standardized self-report mood questionnaire were used to assess cognitive function. RESULTS: Vigilance consistently improved with supplemental carbohydrates in a dose-related manner; the 12% carbohydrate group performed the best and the placebo group the worst (P < 0.001). Mood-questionnaire results corroborated the results from the monitors; the subjects who received carbohydrates reported less confusion (P = 0.040) and greater vigor (P = 0.025) than did those who received the placebo. CONCLUSIONS: Supplemental carbohydrate beverages enhance vigilance and mood during sustained physical activity and interspersed rest. In addition, ambulatory monitoring devices can continuously assess the effects of nutritional factors on cognition as individuals conduct their daily activities or participate in experiments.

Acoustic Stimulation↗

PubMed2002

The effect of creatine monohydrate supplementation on obstacle course and multiple bench press performance.

Dietary creatine (Cr) supplementation has been shown to enhance muscular strength and endurance. This study determined the effects of Cr supplementation on performance of military training tasks. Two groups (Cr and placebo [Pl]) of 13 male soldiers each performed 3 consecutive military obstacle course runs ( approximately 3 minutes over 7 obstacles with a 2-minute rest between runs) followed by a rifle marksmanship task on 3 occasions (T(1), T(2), and T(3)), each separated by 5 days. They also completed a bench press protocol (5 sets to failure at 70% of 1 repetition maximum) and answered the Profile of Mood States questionnaire during each test session. Testing was done 3 times. No supplementation was given before T(1). Supplementation was provided using sports bars, with both groups receiving Pl bars between T(1) and T(2), whereas from T(2) to T(3) the Cr group consumed 24 g per day of Cr monohydrate in sports bars and the Pl group consumed an equal amount (kilocalories) of Pl sports bars. Creatine usage resulted in a significant (14%) increase in total bench press repetitions (p </= 0.05), but no difference between groups in obstacle course run times for the 3 runs from T(2) to T(3). Marksmanship or mood was not affected by Cr supplementation. An increase of 1.4 kg in body mass (p </= 0.005) and a 0.5% decrease in percent body fat (p </= 0.05) were observed after Cr ingestion. Creatine supplementation over 5 days improved performance during a controlled strength test but did not significantly improve military obstacle course performance.

Adult↗