The effects of caffeine on simulated driving, subjective alertness and sustained attention

Determination and estimation of pharmacokinetic profile of caffeine in form of extract of green tea leaves and its analogy with synthetic form

The aim of the study was to formulate and investigate the pharmacokinetic parameters for the tablets of herbal extract of caffeine with comparison to synthetic formulation. The tablets of the aqueous herbal extract of leaves of Camellia sinensis and synthetic caffeine were formulated by wet granulation technique. The HPLC and HPTLC were applied as analytical tools for estimation of caffeine. The batches of formulation (B1 to B7) were subjected for various pre and post-formulation studies. The pharmacokinetic of the batch B5 was assessed in rabbits, and the results were compared to synthetic batch B7. With the suitable pre and post-formulation results, the B5 showed in vitro release of 90.54% of caffeine at the end of 60 min. The release followed first order kinetics and the plot of Higuchi and Peppas confirms anomalous diffusion as the basic mechanism behind the release. B5 revealed non-significant mean C(max), t(1/2), and AUC of 1.88 μg/ml, 5.52 h and 9.67 μg.h/ml respectively compared to B7. The study highlights; no significant difference in the pharmacological effect of caffeine when administered in the form of extract. The administration of herbal extract can further provide the other health benefits lacked by synthetic caffeine.

The Interruptive Effect of Pain on Attention

Pain is known to disrupt attentional performance in both healthy adults and patients with chronic pain. Exactly which aspects of attentional function are affected are, however, still to be determined. The primary aim of this investigation was to systematically examine the effects of experimentally induced pain on a range of attentional performance tasks. Following a review of tests of attentional disruption, seven best candidate tasks were selected and examined across seven experiments. The tasks were: continuous performance, flanker, endogenous precueing, n-back, inhibition, attentional switching, and divided attention. Healthy adult participants performed each of these tasks under three different conditions: a painful heat sensation, a warm heat sensation, and a nonheat control. Pain differentially affected attentional performance across these tasks; pain-related attentional impairment was found on the n-back, attentional switching, and divided attention tasks, but not on the other tasks. This finding suggests that the aspects of attention most affected by pain are those essential for the completion of complex tasks that require the processing of multiple cues and control over attentional deployment. These results are discussed in the context of an emerging view of pain as a demand for executive control and the development of measures that could be used to examine attentional disruption in the context of pain.

Effects of coffee on driving performance during prolonged simulated highway driving

RATIONALE

Coffee is often consumed to counteract driver sleepiness. There is limited information on the effects of a single low dose of coffee on prolonged highway driving in non-sleep deprived individuals.

OBJECTIVES

The aim of this study was to examine the effects of a single cup of coffee (80 mg caffeine) on simulated highway driving performance.

METHODS

Non-sleep deprived healthy volunteers (n024) participated in a double-blind, placebo-controlled, crossover study. After 2 h of monotonous highway driving, subjects received caffeinated or decaffeinated coffee during a 15-min break before continuing driving for another 2 h. The primary outcome measure was the standard deviation of lateral position (SDLP), reflecting the weaving of the car. Secondary outcome measures were speed variability, subjective sleepiness, and subjective driving performance.

RESULTS

The results showed that caffeinated coffee significantly reduced SDLP as compared to decaffeinated coffee, both in the first (p00.024) and second hour (p00.019) after the break. Similarly, the standard deviation of speed (p0 0.024; p00.001), mental effort (p00.003; p00.023), and subjective sleepiness (p00.001; p00.002) were reduced in both the first and second hour after consuming caffeinated coffee. Subjective driving quality was significantly improved in the first hour after consuming caffeinated coffee (p00.004).

CONCLUSIONS

These findings demonstrate a positive effect of one cup of caffeinated coffee on driving performance and subjective sleepiness during monotonous simulated highway driving.

Positive effects of Red Bull® Energy Drink on driving performance during prolonged driving

BACKGROUND

The purpose of this study was to examine if Red Bull® Energy Drink can counteract sleepiness and driving impairment during prolonged driving.

METHODS

Twenty-four healthy volunteers participated in this double-blind placebo-controlled crossover study. After 2 h of highway driving in the STISIM driving simulator, subjects had a 15-min break and consumed Red Bull® Energy Drink (250 ml) or placebo (Red Bull® Energy Drink without the functional ingredients: caffeine, taurine, glucuronolactone, B vitamins (niacin, pantothenic acid, B6, B12), and inositol) before driving for two additional hours. A third condition comprised 4 h of uninterrupted driving. Primary parameter was the standard deviation of lateral position (SDLP), i.e., the weaving of the car. Secondary parameters included SD speed, subjective driving quality, sleepiness, and mental effort to perform the test.

RESULTS

No significant differences were observed during the first 2 h of driving. Red Bull® Energy Drink significantly improved driving relative to placebo: SDLP was significantly reduced during the 3rd (p < 0.046) and 4th hour of driving (p < 0.011). Red Bull® Energy Drink significantly reduced the standard deviation of speed (p < 0.004), improved subjective driving quality (p < 0.0001), and reduced mental effort to perform the test (p < 0.024) during the 3rd hour of driving. Subjective sleepiness was significantly decreased during both the 3rd and 4th hour of driving after Red Bull® Energy Drink (p < 0.001 and p < 0.009, respectively). Relative to uninterrupted driving, Red Bull® Energy Drink significantly improved each parameter.

CONCLUSION

Red Bull® Energy Drink significantly improves driving performance and reduces driver sleepiness during prolonged highway driving.

Glucose and caffeine effects on sustained attention: an exploratory fMRI study

OBJECTIVE

Caffeine and glucose can have beneficial effects on cognitive performance. However, neural basis of these effects remain unknown. Our objective was to evaluate the effects of caffeine and glucose on sustained attention, using functional magnetic resonance imaging (fMRI).

METHODS

Forty young right-handed, healthy, low caffeine-consuming subjects participated in the study. In a double-blind, randomised design, subjects received one of the following beverages: vehicle (water, 150 ml); vehicle plus 75 g of glucose; vehicle plus 75 mg of caffeine; vehicle plus 75 g of glucose and 75 mg of caffeine. Participants underwent two scanning fMRI sessions (before and 30 min after of the administration of the beverage). A continuous performance test was used to assess sustained attention.

RESULTS

Participants who received combined caffeine and glucose had similar performance to the others but had a decrease in activation in the bilateral parietal and left prefrontal cortex.

CONCLUSIONS

Since these areas have been related to the sustained attention and working memory processes, results would suggest that combined caffeine and glucose could increase the efficiency of the attentional system. However, more studies using larger samples and different levels of caffeine and glucose are necessary to better understand the combined effects of both substances.

Effects of caffeine and glucose, alone and combined, on cognitive performance

OBJECTIVE

To study the effects of consuming caffeine and glucose, alone and combined, on cognitive performance.

METHODS

Seventy-two healthy subjects (36 women; age range 18-25) were tested early in the morning, having fasted overnight. Using a double-blind, randomised design, subjects received one of the following beverages: water (150 ml); water plus 75 mg of caffeine; water plus 75 g of glucose; water plus and 75 mg of caffeine and 75 g of glucose. Attention, manual dexterity, visuo-spatial and frontal functions, memory (immediate, consolidation and working) and subjective state were all assessed.

RESULTS

The combination of caffeine and glucose had beneficial effects on attention (sequential reaction time tasks) and on learning and consolidation of verbal memory, effects not being observed when either substance was administered alone. Caffeine only showed improvement in simple reaction time and glucose in simple and one sequential reaction time tasks and in the manual dexterity assembly task.

CONCLUSIONS

The results indicate that the synergistic effects of caffeine and glucose can benefit sustained attention and verbal memory, even with adequate levels of activation of the subjects. However, further studies are required, controlling for different levels of cognitive effort and also considering measurements of neural activity.

Identifying experimental methods to determine the effect of pain on attention: a review of pain, caffeine, alcohol and nicotine studies

OBJECTIVES

To review published studies of the effects that pain and common psychopharmacological substances have on the attentional performance of healthy adults. To identify which attentional tasks have the greatest potential to investigate the effect of pain on attention and provide recommendations for future research.

METHODS

A search was conducted for reports of experimental studies of attention in the context of pain. This was supplemented with studies on attention and caffeine, nicotine and alcohol. Studies were included if they used a healthy adult sample, used experimental or quasi-experimental methods, were relevant to the study of attention or interruption of pain and/or examined the acute effects of a substance on attention.

RESULTS

Thirty-two papers, with 49 different experimental studies were identified (12 pain, 21 nicotine, 7 caffeine, 9 alcohol). Fourteen different tasks were reviewed across six domains of attention. The most promising measures of attention were the continuous performance task, flanker task, endogenous pre-cuing task, n-back task, inhibition task and dual task.

CONCLUSIONS

There are reliable tasks that could be used to determine the effects of pain on attention. Future research is required that develops the utility of these tasks to improve our understanding of the effects pain and analgesia have on attentional performance.

Caffeine, cognitive failures and health in a non-working community sample

RATIONALE

Most studies of the effects of caffeine on performance have been conducted in the laboratory and further information is required on the real-life effects of caffeine consumption on cognition. In addition, possible effects of caffeine consumption on a range of health outcomes should also be assessed in these studies to enable cost-benefit analyses to be conducted.

OBJECTIVES

Secondary analyses of a large epidemiological database (N = 3223 non-working participants, 57% female, with a mean age of 49.6 years, range 17-92 years) were conducted to examine associations between caffeine consumption (mean caffeine consumption was 140 mg/day, range 0-1800 mg) and cognitive failures (errors of memory, attention and action) in a non-working sample. Associations between caffeine consumption and physical and mental health problems were also examined.

METHODS

The study involved secondary analyses of a database formed by combining the Bristol Stress and Health at Work and Cardiff Health and Safety at Work studies. Associations between caffeine consumption and frequency of cognitive failures and health outcomes were examined in a sample of non-workers.

RESULTS

After controlling for possible confounding factors significant associations between caffeine consumption and fewer cognitive failures were observed. Initial analyses suggested that many health variables were associated with regular level of caffeine consumption. However, most of the significant effects of caffeine disappeared when demographic and lifestyle factors were controlled for. Consumption of caffeine was, however, associated with a reduced risk of depression. These effects were also observed in separate analyses examining the source of the caffeine (coffee and tea).

CONCLUSIONS

Overall, the results show that caffeine consumption may benefit cognitive functioning in a non-working population. This confirms earlier findings from working samples. This beneficial effect of caffeine was not associated with negative health consequences. Indeed, consumption of caffeine was found to be associated with a reduced risk of depression.

Effects of dietary caffeine on EEG, performance and mood when rested and sleep restricted

RATIONALE

Until recently, little account had been taken of the confounding effects of caffeine withdrawal and withdrawal reversal when examining the net effects of dietary caffeine.

OBJECTIVES

By including a manipulation involving sleep restriction, the present study aimed to extend recent findings from research in which caffeine withdrawal and withdrawal reversal were controlled. The main aims of the study were to examine the net effects of caffeine, as well as its potential restorative effects following sleep restriction, on EEG, performance and mood.

METHOD

A randomised cross-over design was used in which 15 participants alternated weekly between ingesting placebo and caffeine (1.75 mg/kg) three times daily for four consecutive weeks following either usual sleep or sleep restriction. EEG activity was measured at 32 sites during eyes closed, eyes open and performance of a vigilance task.

RESULTS

Modest effects of caffeine were found in the delta and beta bandwidths, but no main effects of caffeine were observed in the theta or alpha bandwidths. Overall, the effects of caffeine on EEG activity were relatively few, weak and inconsistent, and no evidence was found of net restorative effects of caffeine for any outcome variables.

CONCLUSIONS

The findings do not support the use of caffeine as a means for enhancing human function or as an antidote to the negative effects of sleep loss.

Early effects of caffeinated and decaffeinated coffee on subjective state and gender differences

OBJECTIVES

Some previous studies have demonstrated an early effect of caffeine administration on subjective state, but none of them has explored its existence after the administration of decaffeinated coffee, or the possible differences depending on the gender and circadian typology of the subjects. The aim of the present work is to investigate the early effects (10-30 min post-consumption) of a single low dose of caffeine (100 mg) and decaffeinated coffee on sleepiness, subjective activation and affect using a realistic design. The influence of gender and circadian typology is also explored.

METHODS

A randomized double-blind informed placebo controlled procedure was applied to 688 healthy undergraduate volunteers, mean age 22.03+/-2.21 years, 238 men and 450 women. Measures were recorded before and after beverage consumption (10, 20 and 30 min), in two experimental sessions: morning 11:00-13:00 h or afternoon 16:00-18:00 h.

RESULTS

Caffeine administration induced arousing effects (lesser somnolence and greater activation) in all post-consumption records, while the effects of decaffeinated drink were only apparent at 10 min. Caffeine effects were greater in men, and the decaffeinated beverage produced greater effects in women. Circadian typology only showed effects for time of day (morning/afternoon) related with rhythmic expression.

CONCLUSION

Future works should study more accurately the early effect of coffee beverages and the influence of gender, using other parameters which have proven to be sensitive to their administration. The effect of several caffeine doses should also be studied.

Caffeine attenuates practice effects in word stem completion as measured by fMRI BOLD signal

Caffeine ingestion results in increased brain cell metabolism (Nehlig et al. [1992] Brain Res Brain Res Rev 17:139-170) and decreased cerebral blood flow (Field et al. [2003] Radiology 227:129-135; Mulderink et al. [2002] Neuroimage 15:37-44). The current study investigated the effect of caffeine in a word stem completion task using only novel word stems (no repeated stimuli). Resting perfusion was measured with arterial spin labeled perfusion MRI, along with blood oxygenation level-dependent (BOLD) signal before and after ingestion of regular coffee, decaffeinated coffee, and water. Based on previous research (Laurienti et al. [2002] Neuroimage 17:751-757; Mulderink et al. [2002] Neuroimage 15:37-44), we hypothesized that caffeine would result in increased BOLD signal intensity and extent of BOLD activation. As expected, caffeine resulted in a significant decrease in cerebral perfusion. However, both the control and caffeine groups showed an increase in BOLD signal amplitude across two sets of novel word stems. Additionally, the control group showed a 50% reduction in the extent of BOLD activation, while the caffeine group showed no change in activation extent. Neither group showed changes in BOLD baseline signal over time, which had been suggested to mediate caffeine-related BOLD signal changes. The results suggest that caffeine may attenuate general task practice effects that have been described in recent functional MRI studies of word stem completion (Buckner et al. [2000] Brain 123:620-640).

Task-induced fatigue and collisions in adult drivers with attention deficit hyperactivity disorder

OBJECTIVE

This study compares collision involvement between adult drivers with attention deficit hyperactivity disorder (ADHD) and control participants in a simulation experiment designed to enhance the effects of fatigue. Because the effects of ADHD include difficulties in maintaining attention, drivers with ADHD were hypothesized to be more susceptible to the effects of fatigue while driving.

METHODS

Data are drawn from a validated driving simulation study, portions of which were focused on enhancing the effects of fatigue. The simulator data are supplemented with written questionnaire data. Drivers with ADHD were compared with controls.

RESULTS

The self-report data indicated that drivers with ADHD were more likely to report having been involved in an accident within the previous five years. Simulation data showed that time of day of participation in the experiment were significantly related to likelihood of collision, and that these effects were further exacerbated by ADHD status. Participants with ADHD were more likely than controls to be involved in a crash in the simulator regardless of time of day, but the effects were particularly pronounced in the morning, and the rate of increase in accident involvement from the late afternoon into the evening was greater among participants with ADHD. No differences in self-reported sleep patterns or caffeine use were found between participants with ADHD and controls.

CONCLUSIONS

The results suggest that drivers with ADHD became fatigued more quickly than controls. Such drivers thus face greater risk of involvement in accidents on highways or open roadways where the visual and task monotony of the environment contribute to greater driver fatigue.

Differences in pharmacokinetic and electroencephalographic responses to caffeine in sleep-sensitive and non-sensitive subjects

The present study investigated pharmacokinetic and electroencephalographic responses to caffeine (140 mg) in two groups of healthy volunteers reporting, or not, caffeine-related sleep disturbances. Significant differences in caffeine consumption and smoking habits were observed between the two groups. Plasma samples were taken from each subject before (T0) and after caffeine intake at 0.5, 1, 2, 4, 6 and 24 h. Three pharmacokinetic parameters: half-life (t1/2), maximum time (Tmax) and maximum plasma concentration (Cmax) were calculated from caffeine plasma concentration measurements determined by reversed phase HPLC analysis. Caffeine-sensitive subjects showed significantly greater half-life values when calculated on 24 h after the administration than tolerant subjects (p<0.05). Since the elimination kinetics were similar on the first 6 h after caffeine administration, the increased caffeine clearance observed overnight, when smoking was resumed in the control group, may indicate a short delay for the induction of hepatic cytochrome, reported here for the first time. Electrophysiological responses to caffeine, including vigilance and cortical activity, were assessed by ambulatory electroencephalographic (EEG) recorded during a period of 6 h before and after caffeine consumption. Following caffeine intake, the caffeine-intolerant subjects presented an increase in vigilance levels with faster peak alpha, beta frequency and lower delta and theta power when compared to tolerant subjects. Pharmacokinetic parameters and EEG data showed significant differences between sleep-sensitive and control subjects. These variations may be, in part, explained by cigarette smoking and the higher caffeine intake observed in the subjects of the control groups while caffeine sleep-sensitive subjects have a significantly lower caffeine intake, as already reported in previous studies on patients with sleep disturbances.

Effects of caffeine on olfactory and visual learning in the honey bee (Apis mellifera)

Although caffeine is known to improve alertness and arousal in humans and other mammals, its impacts on specific behaviours, including complex cognitive processes, remain controversial. We reasoned that the availability of an easily manipulable, but behaviourally complex invertebrate organism with a simpler nervous system would be beneficial to this field of research. We used a popular behavioural model, the honeybee, to evaluate the effects of caffeine on (1) the development of olfactory learning and (2) the performance in complex learning paradigms, including a 'delayed-match-to-sample' task and visual associative learning. To evaluate the efficacy of caffeine treatment, a variety of doses (0.4-400 ng/1 mg of body mass) were applied topically to tethered individuals. Behavioural testing was performed with either tethered or free-flying adult honeybees. We show that caffeine has marked cognitive effects in this species. In young honeybees, it reduces the age at which restrained individuals are able to learn an olfactory associative task, whereas in older, free-flying bees, caffeine improves both motivation and cognitive performance in complex learning tasks. Our results suggest that the honeybee model may be useful in explaining caffeine-related behavioural changes not only in this species, but also in mammalian systems.

Effects of repeated doses of caffeine on mood and performance of alert and fatigued volunteers

Evidence for behavioural effects of caffeine is well documented in the literature. It is associated with increased subjective alertness, improved reaction time and enhanced encoding of new information. These effects are most prominent in low arousal situations. However, there is an ongoing debate as to whether such changes are in fact improvements or merely a reversal of the negative effects of a period of caffeine withdrawal (e.g. overnight abstinence). To avoid such a confound this study included multiple doses of caffeine which were administered under double-blind conditions to participants who had ingested their normal daily quota of caffeine. In the present study participants were fatigued by carrying out a prolonged testing schedule in the evening. Sixty volunteers, all regular caffeine consumers, took part in the study. They attended for three sessions on separate days. They were instructed to consume normal amounts of caffeinated beverages. Consumption was measured by a diary and saliva samples were taken and caffeine assays conducted. A baseline test session was carried out at 18.00h and following this a double blind placebo controlled caffeine challenge (1.5mg/kg) conducted. The test battery was repeated twice approximately 30 minutes after the caffeine challenge. Following this another drink was administered and the test battery repeated twice more. On one test session volunteers had placebo in both drinks, in another they had caffeine in both drinks and another caffeine in the first and placebo in the second. Order of conditions was balanced across subjects. The results showed that caffeine led to a more positive mood and improved performance on a number of tasks. Different effects of caffeine were seen depending on the person's level of arousal. Linear effects of caffeine dose were also observed. This is evidence against the argument that behavioural changes due to caffeine are merely the reversal of negative effects of a long period of caffeine abstinence. The findings are discussed in relation to both noradrenergic and cholinergic neurotransmitter systems.

Caffeine at work

RATIONALE

There is a large literature on the effects of caffeine on performance. Most of the studies have been conducted in the laboratory and further information is required on the effects of caffeine consumption on performance and safety at work.

OBJECTIVES

The present studies aimed to determine whether the level of caffeine consumption influenced changes in alertness and performance over the working day. Secondary analyses of a large epidemiological database were also conducted to examine associations between caffeine consumption and cognitive failures and accidents at work.

METHODS

In the first study 110 volunteers, all of whom were regular caffeine consumers, rated their alertness and carried out a simple reaction time task before and after work on a Monday and Friday. Caffeine consumption during the day was recorded and volunteers were sub-divided into low and high consumers on the basis of a median split (220 mg/day). The second study involved secondary analyses of a database formed by combining the Bristol Stress and Health at Work and Cardiff Health and Safety at Work studies. In the first analyses associations between caffeine consumption and frequency of cognitive failures were examined in a sample of 1253 white-collar workers. The second set of analyses examined associations between caffeine consumption and accidents at work in a sample of 1555 workers who were especially at risk of having an accident.

RESULTS

The results from the first study showed that those who consumed higher levels of caffeine reported significantly greater increases in alertness over the working day and a significantly smaller slowing of reaction time. The results from the second study demonstrated significant associations between caffeine consumption and fewer cognitive failures and accidents at work. After controlling for possible confounding factors it was found that higher caffeine consumption was associated with about half the risk of frequent/very frequent cognitive failures and a similar reduction in risk for accidents at work.

CONCLUSIONS

Overall, the results from the three analyses show that caffeine consumption may have benefits for performance and safety at work.

Attentional validity effect across the human menstrual cycle varies with basal temperature changes

This study examined the correlation between covert attention and basal temperature change during menstrual cycle phase in 22 adult females. Previous work showing beneficial effects of estrogen on working memory led us to hypothesize that attentional function would be facilitated at the apparent time of ovulation. Menstrual phase was determined through questionnaires and objective measurements of basal body temperature (BBT) spikes over a 1 month period. The cued target detection (CTD) task was used to assess visuospatial attentional performance at three times during the menstrual cycle. The mean reaction times (RTs) to visual targets were measured as a function of menstrual cycle phase, cue type and target location. As predicted, the onset of ovulation showed decreased reaction times and a significant increase in the cue validity effect on the days immediately preceding and following ovulation. The magnitude of the attention validity effect was negatively correlated with the basal temperature rise. Women lacking basal temperature shifts failed to show these changes. Results support the conclusion that the natural fluctuations of body temperature, and possibly reproductive hormones, during the menstrual cycle may enhance the attentional component of cognitive performance.

The effects of caffeine and expectancy on attention and memory

The present study contrasted caffeine's effects on individuals who expect caffeine to stimulate them and those who do not. Secondly, whether a message that caffeine rather than placebo was administered would also affect these two groups of subjects differently was investigated. The study was conducted single-blind in a 2x2x2 mixed design. The between subjects factor was whether they expected caffeine to stimulate them (E+) or not (E-) according to their self reports obtained before the experiment began. The within subjects factors were message (told caffeine vs told placebo) and beverage type (given caffeine vs placebo). Sixteen subjects in each group (n=32) performed on signal detection, memory scanning and delayed free recall tasks following ingestion of either caffeinated or decaffeinated coffee on two sessions each, a total of four experimental sessions. On each session, subjects were given a message regarding their drink (told caffeine vs told placebo). However, on two sessions there was a mismatch between the message and drink given. For signal detection, performance under caffeine was better than placebo in the E+ but not the E- group. However, subjects in the E+ group did not benefit more than the E- group in either message condition. On memory scanning, detections and false alarms did not differ for either beverage, nor was there a differential finding in the E+ and E- groups. However, reaction time under caffeine condition was shorter. No effects of message were found. Caffeine and message also did not have any effect on performance on the delayed free recall task. The hypothesis that caffeine and message would affect E+ and E- subjects differentially was partly supported.

Caffeine has no effect on measures of cortical excitability

OBJECTIVE

To assess the effect of caffeine on motor thresholds, short interval intra-cortical inhibition (SICI), intra-cortical facilitation (ICF) and cortical silent periods in a placebo controlled double-blinded trial.

METHODS

In eleven healthy non-smoking subjects the following parameters were measured using transcranial magnetic stimulation (TMS): motor thresholds (rest, RMT and active, AMT), SICI and ICF at different conditioning stimulus intensities (60, 70, 80, 90% AMT), cortical silent periods at 130, 150 and 175% AMT, and size of motor evoked potential at rest at 110, 125 and 150% RMT. Measurements were repeated after one cup of decaffeinated coffee. On another day, measurements were obtained before and after one cup of decaffeinated coffee that contained caffeine (3 mg/kg bodyweight). Caffeine concentrations were measured in serum before and after experiments. Experiments were conducted and data were evaluated blinded to the experimental condition.

RESULTS

The results of repeated measurements of all parameters were similar comparing experiments on each day, or when comparing the caffeine arm of the study with the placebo arm.

CONCLUSIONS

Caffeine in a concentration similar to that in a strong cup of coffee does not have a major effect on TMS measures of motor cortex excitability.

SIGNIFICANCE

In healthy controls, the design of TMS experiments that investigate the parameters assessed in this TMS study does not need to control for caffeine.

Pharmacotherapy for excessive daytime sleepiness

Excessive daytime sleepiness (EDS) has recognized detrimental consequences such as road traffic accidents, impaired psychological functioning and reduced work performance. EDS can result from multiple causes such as sleep deprivation, sleep fragmentation, neurological, psychiatric and circadian rhythm disorders. Treating the underlying cause of EDS remains the mainstay of therapy but in those who continue to be excessively sleepy, further treatment may be warranted. Traditionally, the amphetamine derivatives, methylphenidate and pemoline (collectively sympathomimetic) psychostimulants were the commonest form of therapy for EDS, particularly in conditions such as narcolepsy. More recently, the advent of modafinil has broadened the range of therapeutic options. Modafinil has a safer side-effect profile and as a result, interest in this drug for the management of EDS in other disorders, as well as narcolepsy, has increased considerably. There is a growing school of thought that modafinil may have a role to play in other indications such as obstructive sleep apnea/hypopnea syndrome already treated by nasal continuous positive airway pressure but persisting EDS, shift work sleep disorders, neurological causes of sleepiness, and healthy adults performing sustained operations, particularly those in the military. However, until adequately powered randomised-controlled trials confirm long-term efficacy and safety, the recommendation of wakefulness promoters in healthy adults cannot be justified.

Caffeine and central noradrenaline: effects on mood, cognitive performance, eye movements and cardiovascular function

There have been numerous studies on the effects of caffeine on behaviour and cardiovascular function. It is now important to clarify the mechanisms that underlie such effects, and the main objective of the present study was to investigate whether changes in central noradrenaline underlie some of the behavioural and cardiovascular effects of caffeine. This was examined using a clonidine challenge paradigm. Twenty-four healthy volunteers were assigned to one of four conditions: (i) clonidine/caffeine; (ii) clonidine/placebo; (iii) placebo/caffeine: (iv) placebo/placebo. Baseline measurements of mood, cognitive performance, saccadic eye movements and cardiovascular function were recorded. Subsequently, volunteers were given either clonidine (200 microg) or placebo and consumed coffee containing caffeine (1.5 mg/kg) or placebo. The test battery was then repeated 30 min, 150 min and 270 min later. A second cup of coffee (with the same amount of caffeine as the first) was consumed 120 min after the first cup. The results showed that clonidine reduced alertness, impaired many aspects of performance and slowed saccadic eye movements; caffeine removed many of these impairments. Both clonidine and caffeine influenced blood pressure (clonidine reduced it, caffeine raised it) but the effects appeared to be independent, suggesting that separate mechanisms were involved. In addition, there were some behavioural effects of caffeine that were independent of the clonidine effect (e.g. effects on speed of encoding of new information) and these may reflect other neurotransmitter systems (e.g cholinergic effects). Overall, the results suggest that caffeine counteracts reductions in the turnover of central noradrenaline. This mechanism may underlie the beneficial effects of caffeine seen in low alertness states.

Effects of 5 weeks of administration of fluoxetine and dothiepin in normal volunteers on sleep, daytime sedation, psychomotor performance and mood

This was a placebo-controlled, double-blind randomized crossover study of long-term (5 weeks) administration of fluoxetine (20 mg/day) and dothiepin (75 mg/day for 1 week followed by 150 mg/day for 4 weeks) in 12 healthy male volunteers. Subjects were studied on day 10 and day 36 of treatment, with tests of nocturnal sleep, driving performance, continuous electroencephalogram (EEG), sleep during scheduled naps, computerized visual attention tasks, saccadic eye movement measurement and visual analogue ratings of mood. Both drugs had a marked suppressive effect on nocturnal rapid eye movement (REM) sleep; these effects were less at 36 days than at 10 days, and fluoxetine decreased and dothiepin increased REM in daytime naps. Sleep fragmentation after fluoxetine is similar to that reported in the literature. We found no sleep-promoting effects of dothiepin, in contrast to our previous single-dose study, and no subjective sleep effects of either drug. Subjects were less sleepy after both antidepressants than placebo at 5 weeks measured by sleep latencies and EEG. Saccadic eye movement measures were significantly faster after 5 weeks of fluoxetine than after 5 weeks of placebo. Reaction times to a peripheral stimulus during computerized tracking task were shorter after 10 days of dothiepin compared with placebo. Driving performance, visual attention and mood ratings showed no treatment effects. Subjective health reports during each 5 weeks of treatment were similar in number for the two drugs but showed a different profile of side-effects.

Effects of caffeine on human behavior

The literature suggests that the following effects on behavior of adult humans may occur when individuals consume moderate amounts of caffeine. (1) Caffeine increases alertness and reduces fatigue. This may be especially important in low arousal situations (e.g. working at night). (2) Caffeine improves performance on vigilance tasks and simple tasks that require sustained response. Again, these effects are often clearest when alertness is reduced, although there is evidence that benefits may still occur when the person is unimpaired. (3) Effects on more complex tasks are difficult to assess and probably involve interactions between the caffeine and other variables which increase alertness (e.g. personality and time of day). (4) In contrast to the effects of caffeine consumption, withdrawal of caffeine has few effects on performance. There is often an increase in negative mood following withdrawal of caffeine, but such effects may largely reflect the expectancies of the volunteers and the failure to conduct "blind" studies. (5) Regular caffeine usage appears to be beneficial, with higher users having better mental functioning. (6) Most people are very good at controlling their caffeine consumption to maximise the above positive effects. For example, the pattern of consumption over the day shows that caffeine is often consumed to increase alertness. Indeed, many people do not consume much caffeine later in the day since it is important not to be alert when one goes to sleep. In contrast to effects found from normal caffeine intake, there are reports that have demonstrated negative effects when very large amounts are given or sensitive groups (e.g. patients with anxiety disorders) were studied. In this context caffeine has been shown to increase anxiety and impair sleep. There is also some evidence that fine motor control may be impaired as a function of the increase in anxiety. Overall, the global picture that emerges depends on whether one focuses on effects that are likely to be present when caffeine is consumed in moderation by the majority of the population or on the effects found in extreme conditions. The evidence clearly shows that levels of caffeine consumed by most people have largely positive effects on behavior. Excessive consumption can lead to problems, especially in sensitive individuals.