Effects of caffeine on mood and memory

The effects of caffeine and d-amphetamine on spatial span task in healthy participants

Studies that examined the effect of amphetamine or caffeine on spatial working memory (SWM) and verbal working memory (VWM) have used various tasks. However, there are no studies that have used spatial span tasks (SSTs) to assess the SWM effect of amphetamine and caffeine, although some studies have used digit span tasks (DST) to assess VWM. Previous reports also showed that increasing dopamine increases psychosis-like experiences (PLE, or schizotypy) scores which are in turn negatively associated with WM performance in people with high schizotypy and people with schizophrenia. Therefore, the present study aimed to examine the influence of d-amphetamine (0.45 mg/kg, PO), a dopamine releasing stimulant, on SST, DST, and on PLE in healthy volunteers. In a separate study, we examined the effect of caffeine, a nonspecific adenosine receptor antagonist with stimulant properties, on similar tasks.

METHODS

Healthy participants (N = 40) took part in two randomized, double-blind, counter-balanced placebo-controlled cross-over pilot studies: The first group (N = 20) with d-amphetamine (0.45 mg/kg, PO) and the second group (N = 20) with caffeine (200 mg, PO). Spatial span and digit span were examined under four delay conditions (0, 2, 4, 8 s). PLE were assessed using several scales measuring various aspects of psychosis and schizotypy.

RESULTS

We failed to find an effect of d-amphetamine or caffeine on SWM or VWM, relative to placebo. However, d-amphetamine increased a composite score of psychosis-like experiences (p = 0.0005), specifically: Scores on Brief Psychiatric Rating Scale, Perceptual Aberrations Scale, and Magical Ideation Scale were increased following d-amphetamine. The degree of change in PLE following d-amphetamine negatively and significantly correlated with changes in SWM, mainly at the longest delay condition of 8 s (r = -0.58, p = 0.006).

CONCLUSION

The present results showed that moderate-high dose of d-amphetamine and moderate dose of caffeine do not directly affect performances on DST or SST. However, the results indicate that d-amphetamine indirectly influences SWM, through its effect on psychosis-like experiences.

TRIAL REGISTRATION

CLINICAL TRIAL REGISTRATION NUMBER

CT-2018-CTN-02561 (Therapeutic Goods Administration Clinical Trial Registry) and ACTRN12618001292268 (The Australian New Zealand Clinical Trials Registry) for caffeine study, and ACTRN12608000610336 for d-amphetamine study.

EEG Microstates in Early Phase Psychosis: The Effects of Acute Caffeine Consumption

Individuals with schizophrenia use on average twice as much caffeine than the healthy population, but the underlying cortical effects of caffeine in this population are still not well understood. Using resting electroencephalography (EEG) data, we can determine recurrent configurations of the electric field potential over the cortex. These configurations, referred to as microstates, are reported to be altered in schizophrenia and can give us insight into the functional dynamics of large-scale brain networks. In the current study, we use a placebo-controlled, randomized, double-blind, repeated-measures design to examine the effects of a moderate dose of caffeine (200mg) on microstate classes A, B, C, and D in a sample of individuals within the first five years of psychosis onset compared to healthy controls. The results support the reduction of microstate class C and D, as well as the increase of microstate class A and B in schizophrenia. Further, acute caffeine administration appears to exacerbate these group differences by reducing class D, and increasing occurrences of class A and B states in the patient group only. The current results support the hypothesis of a microstate class D reduction as an endophenotypic marker for psychosis and provide the first descriptive account of how caffeine is affecting these microstate classes in an early phase psychosis sample.

Alteration of Resting Electroencephalography by Acute Caffeine Consumption in Early Phase Psychosis

Individuals with schizophrenia use twice as much caffeine on average when compared to healthy controls. Knowing the high rates of consumption, and the potential negative effects of such, it is important we understand the cortical mechanisms that underlie caffeine use, and the consequences of caffeine use on neural circuits in this population. Using a randomized, placebo controlled, double-blind, repeated measures design, the current study examines caffeine's effects on resting electroencephalography (EEG) power in those who have been recently diagnosed with schizophrenia (SZ) compared to regular-using healthy controls (HC). Correlations between average caffeine consumption, withdrawal symptoms, drug related symptoms and clinical psychosis symptoms were measured and significant correlations with neurophysiological data were examined. Results showed caffeine had no effect on alpha asymmetry in the SZ group, although caffeine produced a more global effect on the reduction of alpha₂ power in the SZ group. Further, those with more positive symptoms were found to have a greater reduction in alpha₂ power following caffeine administration. Caffeine also reduced beta power during eyes closed and eyes open resting in HC, but only during eyes closed resting conditions in the SZ group. These findings provide a descriptive profile of the resting EEG state following caffeine administration in individuals with schizophrenia. The findings ultimately suggest caffeine does not affect alpha or beta power as readily in this population and a higher dose may be needed to achieve the desired effects, which may elucidate motivational factors for high caffeine use.

Affective response to physical activity as a deep phenotype in a non-randomized pilot study

Large-scale genomic studies are beginning to identify genetic predictors of physical activity (PA). For those genetically predisposed to engage in low PA, a behavioral intervention may target a malleable factor that mediates genetic predisposition to low PA (i.e., intermediate phenotype) to mitigate the genetic influences. In a non-randomized exercise promotion pilot study, we test the feasibility of examining affective response to PA (how one feels during PA) as an intermediate phenotype between genetic variation and PA adherence. We hypothesized that three single nucleotide polymorphisms (SNPs; rs8044769 and rs3751812 in FTO; rs6265 in BDNF), identified from a prior systematic review, would be predictive of affective response to PA, and that affective response to PA would mediate the SNP-PA link. Forty five healthy, low-active adults received a 12-week print-based PA promotion program. Baseline affective response to PA was assessed using the Feeling Scale, a single-item measure of affective valence. Moderate to vigorous PA (MVPA) was assessed using accelerometers pre- and post-intervention. We examined the three SNPs in a weighted genetic score. Age, sex, body mass index, race, and neighborhood walkability were potential covariates. Affective response to PA and MVPA at follow-up (minutes/day over 4-7 days) were regressed on variation in SNPs, controlling for covariates. One unit increase in genetic score was associated with a 0.14 higher mean Feeling Scale, though was not statistically significant (p = 0.13). Among individual SNPs, having an additional FTO rs8044769 C allele was associated with a mean Feeling Scale score of 0.53 units higher (p = 0.015), which was statistically significant after applying the corrected p-value of 0.016. The genetic score or individual SNPs were not predictive of MVPA 12 weeks later, thereby mediation analyses were not performed. The preliminary findings demonstrate the promise of the intermediate phenotype approach.

Green tea consumption and the management of adrenal stress hormones in adolescents who stutter

Green tea and its polyphenolic compounds have been shown to exert positive effects in individuals with psychological disorders. The protective role of green tea against stuttering or its related consequences, depression, anxiety and stress, were evaluated in adolescents with moderate stuttering (MS). A total of 60 adolescents aged (12-18) years old were enrolled in this study. Patients were classified according to standardized test material Stuttering Severity Instrument, 4th Edition was used to estimate the severity of stuttering; participants were classified into two groups: a normal healthy group (n=30) and a MS group (n=30). The Depression Anxiety Stress Scale and General Health Questionnaire were used to estimate the degree of depression, anxiety and stress as well as general mental health. The physiological profile of stress hormones, as a measure of the response to green tea response, was also measured amongst participants. Adrenal stress hormones cortisol, dehydroepiandrosterone (DHEA), acetylcholine (ACTH), corticosterone and the cortisol:DHEA ratio were assayed. In addition, the constituent green tea polyphenols and their quantities were determined using liquid chromatography analysis. Decaffeinated green tea was administered six cups/day for 6 weeks, and this significantly improved the depression, anxiety, stress and mental health consequences associated with stuttering in adolescents. In addition, increased consumption of green tea significantly reduced elevated levels of adrenal stress hormones; cortisol, DHEA, ACTH and corticosterone, and increased the cortisol:DHEA ratio in the control and adolescents who stuttered. The data showed that drinking six cups of decaffeinated green tea, which is enriched in catechins (1,580 mg) and other related polyphenols, was sufficient to improve the consequences of mental health associated with stuttering in younger aged individuals.

How does caffeine influence memory? Drug, experimental, and demographic factors

Caffeine is a widely used nootropic drug, but its effects on memory in healthy participants have not been sufficiently evaluated. Here we review evidence of the effects of caffeine on different types of memory, and the associated drug, experimental, and demographical factors. There is limited evidence that caffeine affects performance in memory tasks beyond improved reaction times. For drug factors, a dose-response relationship may exist but findings are inconsistent. Moreover, there is evidence that the source of caffeine can modulate its effects on memory. For experimental factors, past studies often lacked a baseline control for diet and sleep and none discussed the possible reversal of withdrawal effect due to pre-experimental fasting. For demographic factors, caffeine may interact with sex and age, and the direction of the effect may depend on the dose, individual tolerance, and metabolism at baseline. Future studies should incorporate these considerations, as well as providing continued evidence on the effect of caffeine in visuospatial, prospective, and implicit memory measures.

Estrous cycle modulates the anxiogenic effects of caffeine in the elevated plus maze and light/dark box in female rats

Caffeine is a commonly used stimulant of the central nervous system that reduces fatigue, increases alertness, and exerts positive effects on emotion through actions on various brain structures. High doses of caffeine can cause headaches, heart palpitations, hyperactivity, and anxiety symptoms. Consequently, reducing the consumption of stimulant substances, such as sugar and caffeine, is proposed to ameliorate symptoms of premenstrual syndrome in women. The administration of steroid hormones has been suggested to modulate the effects of caffeine, but unknown is whether endogenous hormone variations during the estrous cycle modulate the pharmacological effects of caffeine. The present study evaluated the effects of caffeine (10, 20, and 40 mg/kg) during metestrus-diestrus and proestrus-estrus of the ovarian cycle in rats on anxiety-like behavior using the elevated plus maze and light/dark box. During metestrus-diestrus, all doses of caffeine increased anxiety-like behavior, indicated by the main variables in both behavioral tests (i.e., higher Anxiety Index and lower percent time spent on the open arms in the elevated plus maze and less time spent in the light compartment in the light/dark box). During proestrus-estrus, only 20 and 40 mg/kg caffeine increased these parameters of anxiety-like behavior, albeit only slightly. In conclusion, caffeine increased anxiety-like behaviors in metestrus-diestrus, with an attenuation of these effects of lower doses of caffeine in proestrus-estrus. These effects that were observed in metestrus-diestrus and proestrus-estrus may be associated with low and high concentrations of steroid hormones, respectively, that naturally occur during these phases of the ovarian cycle.

Warm Footbaths with Sinapis nigra or Zingiber officinale Enhance Self-Reported Vitality in Healthy Adults More than Footbaths with Warm Water Only: A Randomized, Controlled Trial

Objectives

To examine the effects of warm footbaths with thermogenic medicinal powders on vitality and heart rate variability in healthy adults. Intervention and Outcome. Seventeen healthy young adults (22.1 ± 2.4 years, 11 females) received three footbaths (WA: warm water only; GI: warm water and ginger; MU: warm water and mustard) in randomized order with a crossover design. We assessed vitality with the Basler Befindlichkeit questionnaire (BBS) and heart rate variability (HRV) before (t0), immediately after (t1), and 10 minutes following footbaths (t2). The primary outcome measure was self-reported vitality, measured via the BBS, at t1.

Results

The primary outcome measure, self-reported vitality, was higher after GI and tended to be higher after MU compared to WA with medium effect sizes (GI vs. WA, mean difference −2.47 (95% CI −5.28 to 0.34), p_adj=0.048, d_adj = 0.74), MU vs. WA, −2.35 (−5.32 to 0.61), p_adj=0.30, d_adj = 0.50). At t2, the standard deviation of beat-to-beat intervals (SDNN) of HRV increased, and the stress index tended to decrease after all three footbath conditions with small to medium effect sizes (0.42–0.66).

Conclusion

There is preliminary evidence that footbaths with thermogenic agents GI and MU may increase self-reported vitality during a short-time period with a more pronounced effect with GI. After a short follow-up, all three conditions tended to shift the autonomic balance towards relaxation. Future research should investigate these effects in clinical samples with a larger, more diverse sample size.

Affective response to physical activity as an intermediate phenotype

Over the past seventy years, biomedical and epidemiological research has shown that regular physical activity (PA) is critical for physical and mental health. Despite this knowledge, physical inactivity is the fourth leading risk factor for global mortality, accounting for 9% (5.3 million) of premature deaths annually. We suggest this mismatch between knowing about the risks of PA and engaging in regular PA can be reconciled by focusing less on expected health benefits of PA and more on how people feel during PA. Specifically, in this position paper, we argue that affective response (feeling good versus bad) to PA is an intermediate phenotype that can explain significant variance in PA behavior and is, in turn, a function of genetic variability. In making this argument, we first review empirical evidence showing that affective response to PA predicts future physical activity behavior. Second, we systematically review research on single nucleotide morphisms (SNPs) that are associated with affective response to PA. Investigating affective response to PA as an intermediate phenotype will allow future researchers to move beyond asking "What SNPs are associated with PA?", and begin asking "How do these SNPs influence PA?", thus ultimately optimizing the translation of knowledge gained from genomic data to intervention development.

Genomic predictions and genome-wide association studies based on RAD-seq of quality-related metabolites for the genomics-assisted breeding of tea plants

Effectively using genomic information greatly accelerates conventional breeding and applying it to long-lived crops promotes the conversion to genomic breeding. Because tea plants are bred using conventional methods, we evaluated the potential of genomic predictions (GPs) and genome-wide association studies (GWASs) for the genetic breeding of tea quality-related metabolites using genome-wide single nucleotide polymorphisms (SNPs) detected from restriction site-associated DNA sequencing of 150 tea accessions. The present GP, based on genome-wide SNPs, and six models produced moderate prediction accuracy values (r) for the levels of most catechins, represented by ( -)-epigallocatechin gallate (r = 0.32-0.41) and caffeine (r = 0.44-0.51), but low r values for free amino acids and chlorophylls. Integrated analysis of GWAS and GP detected potential candidate genes for each metabolite using 80-160 top-ranked SNPs that resulted in the maximum cumulative prediction value. Applying GPs and GWASs to tea accession traits will contribute to genomics-assisted tea breeding.

Functional and cognitive responses to caffeine intake in middle-aged women are dose depending

Middle-aged women display many physiological and cognitive alterations resulting from aging and physical inactivity as well as other changes that occur as a function of menopause. Caffeine consumption is highest in this age with women having a particular greater sensitivity to caffeine than men. Its effects on functional and cognitive functions are controversial and seem to depend on the dose intake. This study aimed to assess the effect of low (100mg) and high (400mg) doses of caffeine consumption on cognitive (simple reaction time) and functional (upper and low body muscle endurance, aerobic endurance and functional mobility) performances. These performances were evaluated in 19 healthy middle-aged women by the 30-Second Chair Stand test for lower body muscle endurance, the 30sec Arm Curl Test for upper body muscle endurance, the 2-Minute Step test for aerobic endurance, The Timed Up and Go test for functional mobility and the simple reaction time test for reaction time, 60min after a treatment capsule intake (100mg caffeine/400mg caffeine/placebo). Low caffeine consumption significantly improved (p<.005) cognitive performance, while high caffeine consumption did not. However, the functional performance significantly improved (p<.05) after high caffeine consumption but not after low caffeine consumption. Except, the functional mobility performance significantly improved (p<.05) after both low and high caffeine consumption with better improvement (p<.05) after the high dose. In conclusion, low caffeine consumption improved cognitive performance and high caffeine consumption improved functional performance but the functional mobility improved after both low and high caffeine consumption in middleaged women.

Pharmacological screening of a new alpha-2 adrenergic receptor agonist, mafedine, in zebrafish

Pharmacological agents acting at alpha-2 adrenergic receptors are widely used in physiology and neuroscience research. Mounting evidence of their potential utility in clinical and experimental psychopharmacology, necessitates new models and novel model organisms for their screening. Here, we characterize behavioral effects of mafedine (6-oxo-1-phenyl-2- (phenylamino)-1,6-dihydropyrimidine-4-sodium olate), a novel drug with alpha-2 adrenergic receptor agonistic effects, in adult zebrafish (Danio rerio) in the novel tank test of anxiety and activity. Following an acute 20-min exposure, mafedine at 60 mg/L produced a mild psychostimulant action with some anxiogenic-like effects. Repeated acute 20-min/day administration of mafedine for 7 consecutive days at 1, 5 and 10 mg/L had a similar action on fish behavior as an acute exposure to 60 mg/L. Since mafedine demonstrated robust behavioral effects in zebrafish - a sensitive vertebrate aquatic model, it is likely that it may modulate rodent and human behavior as well. Thus, further studies are needed to explore this possibility in detail, and whether it may foster clinical application of mafedine and related alpha-2 adrenergic agents.

The mediating role of mood in the relationship between perseverative cognition, sleep and subjective health complaints in music students

OBJECTIVE

Subjective health complaints (SHC) are frequent in musicians. These complaints may be particularly distressing in this population because they are performance relevant. This paper aims at testing a model positing that (a) perseverative cognition (PC) predicts sleep duration/quality, (b) sleep duration/quality predicts SHC and (c) mood is a mediator of these associations.

DESIGN

Participants were 72 music students (mean age (SD): 22.7 (3.0) years), and the assessment period consisted of seven consecutive days, with a solo performance on the fifth day.

MAIN OUTCOME MEASURES

Self-reported total sleep time (TST) and sleep quality were assessed 30 min after wake-up, and objective TST/sleep quality were assessed with an actigraphy watch. PC and mood were measured five times a day. Daily SHC were assessed at 9 p.m.

RESULTS

PC did not significantly predict sleep duration/quality. Self-reported and objective TST and sleep quality were all significantly associated with SHC. Mood played a mediating role in each of these relationships with the exception of objective sleep quality.

CONCLUSION

The tested model on the association among PC, sleep and SHC and the mediating role of mood received partial support, highlighting the importance of sleep and mood in the emergence of SHC among university music students.

Acute Administration of Caffeine: The Effect on Motor Coordination, Higher Brain Cognitive Functions, and the Social Behavior of BLC57 Mice

Excessive caffeine consumption causes adverse health effects. The effects of moderate and high doses of caffeine consumption on the motor coordination, cognitive brain functions, and the social behavior in mice were studied. Animals were divided into three groups: control group, moderate dose group (Ac MD), and high dose group (Ac HD). The animals were tested after 7 days of caffeine administration. A rotarod test for motor coordination showed that the mice of the moderate dose group could stay on the rotating rod longer before falling in comparison to the control group and the high dose group. A water maze test for learning and memory showed better performance of mice receiving the moderate dose of caffeine compared to the other groups. Animals that were administered moderate as well as high doses of caffeine showed no sociability and no preference for social novelty in the three-chamber test used to test social behavior. In an elevated plus maze test, control animals showed no anxiety-like behavior while mice from both of the groups administered with caffeine showed anxiety-like behaviors. Our data conclude that the effects of caffeine on higher brain functions depend on the administration dose. When caffeine was given in moderate doses, it resulted in enhancement of memory and motor coordination functions. However, high doses caused defects in memory and learning. The social behavior of the mice, as determined by the level of anxiety and sociability, was affected negatively by moderate as well as high dose caffeine administration.

The Effects of Carbohydrates, in Isolation and Combined with Caffeine, on Cognitive Performance and Mood-Current Evidence and Future Directions

This review examines the effects of carbohydrates, delivered individually and in combination with caffeine, on a range of cognitive domains and subjective mood. There is evidence for beneficial effects of glucose at a dose of 25 g on episodic memory, but exploration of dose effects has not been systematic and the effects on other cognitive domains is not known. Factors contributing to the differential sensitivity to glucose facilitation include age, task difficulty/demand, task domain, and glucoregulatory control. There is modest evidence to suggest modulating glycemic response may impact cognitive function. The evidence presented in this review identifies dose ranges of glucose and caffeine which improve cognition, but fails to find convincing consistent synergistic effects of combining caffeine and glucose. Whilst combining glucose and caffeine has been shown to facilitate cognitive performance and mood compared to placebo or glucose alone, the relative contribution of caffeine and glucose to the observed effects is difficult to ascertain, due to the paucity of studies that have appropriately compared the effects of these ingredients combined and in isolation. This review identifies a number of methodological challenges which need to be considered in the design of future hypothesis driven research in this area.

Effects of acute caffeine on anxiety-related behavior in rats chronically exposed to the drug, with some evidence of possible withdrawal-reversal

For 20days male and female PVG/c hooded rats were provided with caffeinated (approximately 50mg/kg/day) or unadulterated drinking water, and then their anxiety-related behavior was observed in an open field and elevated plus maze. Their choices of a brightness change were also observed in a Y maze to assess any caffeine effects on spatial memory. 24h later, all rats were tested again following an intraperitoneal injection of 50mg/kg acute caffeine, or vehicle. Earlier chronic caffeine decreased ambulation, walking, rearing, center occupancy and increased immobility in the open field thereby suggesting increased anxiety. However, occupancy of the plus-maze open arms and the Y-maze novel arm were increased by caffeine for male rats, but decreased for females probably because of sex differences in control levels of the response rather than to drug effects on anxiety and memory respectively. Following caffeine withdrawal, acute caffeine had the opposite effect to chronic treatment namely, increased open-field ambulation, walking, center occupancy and decreased immobility and defecation for caffeine-naïve rats that were suggestive of decreased anxiety. Similar but more consistent effects (plus decreased emergence latencies from a darkened start box into the open field) also typified the caffeine-experienced rats which in this case may have been accentuated by caffeine withdrawal-reversal. There was no evidence of either chronic or acute caffeine affecting spatial memory measured in the Y maze. There were also examples of lower overall activity and higher anxiety in male rats, than in females, and some sex-dependent caffeine effects.

Behavioral profile assessment in offspring of Swiss mice treated during pregnancy and lactation with caffeine

The association between caffeine consumption and various psychiatric manifestations has long been observed. The objective was to assess the behavioral profile in offspring of Swiss mice treated during pregnancy and lactation with caffeine. For this purpose, two groups (n = 6 each and BW ~ 35 g) of female mice were treated during pregnancy and lactation by: tap water and caffeine solution at a concentration of 0.3 mg/mL through oral route. The offspring obtained, by completing 70 days of life, was underwent a behavioral battery test. Statistical analysis was performed by student t test and the different significance adopted was p < 0.05. According to our results, it was not found any significant differences in tail suspension and forced swimming tests. In anxiety related responses however, the mice of caffeine group had greater number of fecal pellets (178 %, p = 0.001) in the open field test, higher number of attempts (51 %, p = 0.03) in light-dark box and decreased percentage of entries in open arms (41 %, p = 0.01) in elevated plus maze test. Moreover, in the marble burying test, there was a significant decrease in the number of buried marbles compared with controls (110 %, p = 0,002). In the meantime, in the von Frey test, it was observed an exacerbation of mechanical allodynia both in basal conditions and after the carrageenan administration (p < 0.001). Furthermore, caffeine treatment during pregnancy and lactation causes long-term behavioral changes in the mice offspring that manifest later in life.

Caffeine's influence on object recognition and working-memory in prepubertal mice and its modulation by gender

OBJECTIVE

This study investigated the effects of intraperitoneal injection of caffeine on Y-maze working-memory and novel object recognition (NOR) in prepubertal mice.

METHODOLOGY

Y-maze spontaneous alternation and a novel object recognition test (consisting of acclimation, acquisition and test phases) were performed. Mice received a single dose of caffeine (10, 20, 40, 80 and 120mgkg(-1) i.p.) or vehicle, 30min before Y-maze exploration. For the NOR test, caffeine was given 30min before training and another dose 30min before test phase.

RESULTS

NOR time (acquisition phase) increased significantly in males at all doses of caffeine and decreased in females at 10, 20 and 40mg/kg compared to vehicle; during the test phase, novel object exploration time decreased significantly in males and increased in females at 10 and 20mg/kg only to decrease again at 120mg/kg. Recognition index decreased in males and increased in females while, males showed poor discrimination between novel and familiar objects compared to vehicle; while females showed increased discrimination between novel and familiar object at 10, 20,40 and 80mg/kg and a decrease at 120mg/kg. Y-maze spontaneous alternation improved significantly in males at 10 and 40mg/kg and decreased at 20 and 120mg/kg in females.

CONCLUSION

The findings suggest that acute caffeine injection improves non-spatial memory retention in female mice but not in males; spatial working-memory is however improved in males but not in females.

Cumulative neurobehavioral and physiological effects of chronic caffeine intake: individual differences and implications for the use of caffeinated energy products

The use of caffeine-containing energy products has increased worldwide in recent years. All of the top-selling energy drinks contain caffeine, which is likely to be the primary psychoactive ingredient in these products. Research shows that caffeine-containing energy products can improve cognitive and physical performance. Presumably, individuals consume caffeine-containing energy products to counteract feelings of low energy in situations causing tiredness, fatigue, and/or reduced alertness. This review discusses the scientific evidence for sleep loss, circadian phase, sleep inertia, and the time-on-task effect as causes of low energy and summarizes research assessing the efficacy of caffeine to counteract decreased alertness and increased fatigue in such situations. The results of a placebo-controlled experiment in healthy adults who had 3 nights of total sleep deprivation (with or without 2-hour naps every 12 hours) are presented to illustrate the physiological and neurobehavioral effects of sustained low-dose caffeine. Individual differences, including genetic factors, in the response to caffeine and to sleep loss are discussed. The review concludes with future directions for research on this important and evolving topic.

The effect of caffeine on spontaneous pupillary oscillations

PURPOSE

Caffeine stimulates the central nervous system, but the duration and extent of its influence on the pupil are not known. The aim of this study was to determine whether caffeine could have an effect on pupillary sleepiness waves, measured with the Pupillographic Sleepiness Test (PST) during routine clinical PST testing, where the caffeine dose-response of a participant cannot be registered before recording.

METHODS

Twenty participants (aged between 22 and 51 years, (mean 30.9 years ± 8.9 SD, 11 women and nine men),.were tested at seven different time-points over 4.5 h. Each participant was tested under four conditions with coffee drunk or not between 1 and 2 h before the first measurement and/or 15 min afterwards.

RESULTS

Caffeine caused a reduction in the Pupillary Unrest Index (PUI) with a maximal effect 1.25 h after consumption. A prolonged effect is found if coffee was consumed between 1 and 2 h before the first measurement. More excessive coffee consumers show prolongation of the effect. Subjective scales of sleepiness, alertness and craving for caffeine were significantly correlated to linear logarithm of PUI (lnPUI).

CONCLUSIONS

We conclude that caffeine causes a dampening of the pupillary oscillations in well-rested participants. As caffeine consumption can affect the PST for up to 6.5 h after intake, it is recommended that if PST measurements are to be carried out in the morning, caffeine consumption should not be allowed after midnight.

Psychostimulants and cognition: a continuum of behavioral and cognitive activation

Psychostimulants such as cocaine have been used as performance enhancers throughout recorded history. Although psychostimulants are commonly prescribed to improve attention and cognition, a great deal of literature has described their ability to induce cognitive deficits, as well as addiction. How can a single drug class be known to produce both cognitive enhancement and impairment? Properties of the particular stimulant drug itself and individual differences between users have both been suggested to dictate the outcome of stimulant use. A more parsimonious alternative, which we endorse, is that dose is the critical determining factor in cognitive effects of stimulant drugs. Herein, we review several popular stimulants (cocaine, amphetamine, methylphenidate, modafinil, and caffeine), outlining their history of use, mechanism of action, and use and abuse today. One common graphic depiction of the cognitive effects of psychostimulants is an inverted U-shaped dose-effect curve. Moderate arousal is beneficial to cognition, whereas too much activation leads to cognitive impairment. In parallel to this schematic, we propose a continuum of psychostimulant activation that covers the transition from one drug effect to another as stimulant intake is increased. Low doses of stimulants effect increased arousal, attention, and cognitive enhancement; moderate doses can lead to feelings of euphoria and power, as well as addiction and cognitive impairment; and very high doses lead to psychosis and circulatory collapse. This continuum helps account for the seemingly disparate effects of stimulant drugs, with the same drug being associated with cognitive enhancement and impairment.

The effects of combined caffeine and glucose drinks on attention in the human brain

The objective of this research was to measure the effects of energising drinks containing caffeine and glucose, upon mental activity during sustained selective attention. Non-invasive electrophysiological brain recordings were made during a behavioural study of selective attention in which participants received either energising or placebo drinks. We tested specifically whether energising drinks have significant effects upon behavioural measures of performance during a task requiring sustained visual selective attention, as well as on accompanying components of the event-related potential (ERPs) related to information processing in the brain. Forty healthy volunteers were blindly assigned to receive either the energising drink or a similar-tasting placebo drink. The behavioural task involved identifying predefined target stimulus among rapidly presented streams of peripheral visual stimuli, and making speeded motor responses to this stimulus. During task performance, accuracy, reaction times and ongoing brain activity were stored for analysis. The energising drink enhanced behavioural performance both in terms of accuracy and speed of reactions. The energising drink also had significant effects upon the event-related potentials. Effects started from the enhancement of the earliest components (Cl/P1), reflecting early visual cortical processing in the energising-drink group relative to the placebo group over the contralateral scalp. The later N1, N2 and P3 components related to decision-making and responses were also modulated by the energising drink. Energising drinks containing caffeine and glucose can enhance behavioural performance during demanding tasks requiring selective attention. The behavioural benefits are coupled to direct effects upon neural information processing.

Caffeine can decrease subjective energy depending on the vehicle with which it is consumed and when it is measured

RATIONALE

Energy drinks contain glucose and caffeine, although in the longer term both adversely influence blood glucose homeostasis, with the unconsidered potential to have adverse consequences for cognition and mood.

OBJECTIVE

The objective of this study was to consider the influence on interstitial glucose levels, mood and cognition of drinks differing in their caffeine content and glycaemic load.

METHODS

Ninety minutes after a standard breakfast, a yoghurt-, glucose- or water-based drink, with or without 80 mg of caffeine, was consumed.

RESULTS

The consumption of caffeine negatively influenced glucose homeostasis: that is, irrespective of the vehicle, caffeine consumption resulted in elevated levels of blood glucose throughout the study. Thirty minutes after consuming caffeine and water, rather than water alone, greater subjective energy was reported. However, after 90 and 150 min, caffeine administered in water increased tiredness, hostility and confusion. In contrast, combining caffeine with a yoghurt-based drink increased energy, agreeableness and clearheadedness later in the morning. There were no effects of caffeine on ratings of mood when it was taken with glucose. Caffeine, irrespective of vehicle, resulted in better memory, quicker reaction times in the choice reaction time test and the working memory task, and better and quicker responses with the vigilance task.

CONCLUSION

Further research should consider how caffeine interacts with macronutrients and the timescale over which such effects occur.

Caffeine prevents weight gain and cognitive impairment caused by a high-fat diet while elevating hippocampal BDNF

Obesity, high-fat diets, and subsequent type 2 diabetes (T2DM) are associated with cognitive impairment. Moreover, T2DM increases the risk of Alzheimer's disease (AD) and leads to abnormal elevation of brain beta-amyloid levels, one of the hallmarks of AD. The psychoactive alkaloid caffeine has been shown to have therapeutic potential in AD but the central impact of caffeine has not been well-studied in the context of a high-fat diet. Here we investigated the impact of caffeine administration on metabolism and cognitive performance, both in control rats and in rats placed on a high-fat diet. The effects of caffeine were significant: caffeine both (i) prevented the weight-gain associated with the high-fat diet and (ii) prevented cognitive impairment. Caffeine did not alter hippocampal metabolism or insulin signaling, likely because the high-fat-fed animals did not develop full-blown diabetes; however, caffeine did prevent or reverse a decrease in hippocampal brain-derived neurotrophic factor (BDNF) seen in high-fat-fed animals. These data confirm that caffeine may serve as a neuroprotective agent against cognitive impairment caused by obesity and/or a high-fat diet. Increased hippocampal BDNF following caffeine administration could explain, at least in part, the effects of caffeine on cognition and metabolism.

Caffeine increases tear volume depending on polymorphisms within the adenosine A2a receptor gene and cytochrome P450 1A2

PURPOSE

The primary aim of the present study was to examine the effect of caffeine on tear volume. The secondary aim was to investigate the relation between caffeine-induced changes in tear volume and polymorphisms in ADORA2A and CYP1A2.

DESIGN

Double-masked, placebo-controlled, crossover study.

PARTICIPANTS

Seventy-eight healthy volunteers were recruited for the study.

METHODS

Subjects participated in 2 sessions in which they received capsules containing either placebo or caffeine. The caffeine capsules were given to the subjects to keep the caffeine volume per body weight within 5 to 7 mg/kg. After caffeine intake, tear meniscus height (TMH) was measured. Subjects provided a blood sample for genotyping.

MAIN OUTCOME MEASURES

Tear meniscus height, single nucleotide polymorphism.

RESULTS

The tear volume increased after caffeine consumption. The net increase in TMH was 0.08 mm (95% confidence interval, 0.05-0.10) greater when participants were given caffeine than when given placebo (P<0.0001). In ADORA2A, the difference in the net increase in TMH for participants who were heterozygous at rs5751876 and rs2298383 was 0.07 mm (P = 0.001) and who were minor homozygous was 0.08 mm (P = 0.007). In CYP1A2, the net increase in TMH for participants who were minor homozygous at rs2472304 was lower than for those who were major homozygous; the difference was 0.06 mm (P = 0.039).

CONCLUSIONS

Caffeine intake increases tear volume and polymorphisms within ADORA2A, and CYP1A2 is associated with the tear increase after caffeine intake. Genetic polymorphisms had a significant effect on tear meniscus that was of limited clinical significance.

Caffeine challenge test and panic disorder: a systematic literature review

This systematic review aimed to examine the results of studies that have investigated the induction of panic attacks and/or the anxiogenic effect of the caffeine challenge test in patients with panic disorder. The literature search was performed in PubMed, Biblioteca Virtual em Saúde and the ISI Web of Knowledge. The words used for the search were caffeine, caffeine challenge test, panic disorder, panic attacks and anxiety disorder. In total, we selected eight randomized, double-blind studies where caffeine was administered orally, and none of them controlled for confounding factors in the analysis. The percentage of loss during follow-up ranged between 14.3% and 73.1%. The eight studies all showed a positive association between caffeine and anxiogenic effects and/or panic disorder.

Influences of audio-visual environments on feelings of deliciousness during having sweet foods: an electroencephalogram frequency analysis study

Feelings of deliciousness during having foods are mainly produced by perceptions of sensory information extracted from foods themselves, such as taste and olfaction. However, environmental factors might modify the feeling of deliciousness. In the present study, we investigated how the condition of audio-visual environments affects the feeling of deliciousness during having sweet foods. Electroencephalograms (EEGs) were recorded from the frontal region of the scalp of healthy participants under virtual scenes of tearoom and construction work, respectively. The participants were asked to rate deliciousness after the recordings. Frequency analyses were performed from the EEGs. During having the foods, occupancy rates of beta frequency band between tearoom scenes and construction work scenes were markedly different, but not in other frequency bands. During having no food, in contrast, there was no difference of occupancy rates in respective frequency bands between the two different scenes. With regard to deliciousness during having sweet foods, all participants rated high scores under the scenes of tearoom than those under the scenes of construction work. Interestingly, there is a positive correlation between occupancy rates of beta frequency band and scores of deliciousness. These findings suggest that comfortable audio-visual environments play an important role in increasing the feeling of deliciousness during having sweet foods, in which beta frequency rhythms may be concerned with producing comprehensive feelings of deliciousness.

Purinergic signalling: from normal behaviour to pathological brain function

Purinergic neurotransmission, involving release of ATP as an efferent neurotransmitter was first proposed in 1972. Later, ATP was recognised as a cotransmitter in peripheral nerves and more recently as a cotransmitter with glutamate, noradrenaline, GABA, acetylcholine and dopamine in the CNS. Both ATP, together with some of its enzymatic breakdown products (ADP and adenosine) and uracil nucleotides are now recognised to act via P2X ion channels and P1 and P2Y G protein-coupled receptors, which are widely expressed in the brain. They mediate both fast signalling in neurotransmission and neuromodulation and long-term (trophic) signalling in cell proliferation, differentiation and death. Purinergic signalling is prominent in neurone-glial cell interactions. In this review we discuss first the evidence implicating purinergic signalling in normal behaviour, including learning and memory, sleep and arousal, locomotor activity and exploration, feeding behaviour and mood and motivation. Then we turn to the involvement of P1 and P2 receptors in pathological brain function; firstly in trauma, ischemia and stroke, then in neurodegenerative diseases, including Alzheimer's, Parkinson's and Huntington's, as well as multiple sclerosis and amyotrophic lateral sclerosis. Finally, the role of purinergic signalling in neuropsychiatric diseases (including schizophrenia), epilepsy, migraine, cognitive impairment and neuropathic pain will be considered.

Sleep deprivation prevents stimulation-induced increases of levels of P-CREB and BDNF: protection by caffeine

It is well known that caffeine and sleep deprivation have opposing effects on learning and memory; therefore, this study was undertaken to determine the effects of chronic (4wks) caffeine treatment (0.3g/l in drinking water) on long-term memory deficit associated with 24h sleep deprivation. Animals were sleep deprived using the modified multiple platform method. The results showed that chronic caffeine treatment prevented the impairment of long-term memory as measured by performance in the radial arm water maze task and normalized L-LTP in area CA1 of the hippocampi of sleep-deprived anesthetized rats. Sleep deprivation prevents the high frequency stimulation-induced increases in the levels of phosphorylated-cAMP response element binding protein (P-CREB) and brain-derived neurotrophic factor (BDNF) seen during the expression of late phase long-term potentiation (L-LTP). However, chronic caffeine treatment prevented the effect of sleep-deprivation on the stimulated levels of P-CREB and BDNF. The results suggest that chronic caffeine treatment may protect the sleep-deprived brain probably by preserving the levels of P-CREB and BDNF.

Adenosine A(2A) receptors in psychopharmacology: modulators of behavior, mood and cognition

The adenosine A(2A) receptor (A(2A)R) is in the center of a neuromodulatory network affecting a wide range of neuropsychiatric functions by interacting with and integrating several neurotransmitter systems, especially dopaminergic and glutamatergic neurotransmission. These interactions and integrations occur at multiple levels, including (1) direct receptor- receptor cross-talk at the cell membrane, (2) intracellular second messenger systems, (3) trans-synaptic actions via striatal collaterals or interneurons in the striatum, (4) and interactions at the network level of the basal ganglia. Consequently, A(2A)Rs constitute a novel target to modulate various psychiatric conditions. In the present review we will first summarize the molecular interaction of adenosine receptors with other neurotransmitter systems and then discuss the potential applications of A(2A)R agonists and antagonists in physiological and pathophysiological conditions, such as psychostimulant action, drug addiction, anxiety, depression, schizophrenia and learning and memory.

Approaches to measuring the effects of wake-promoting drugs: a focus on cognitive function

OBJECTIVES

In clinical drug development, wakefulness and wake-promotion may be assessed by a large number of scales and questionnaires. Objective assessment of wakefulness is most commonly made using sleep latency/maintenance of wakefulness tests, polysomnography and/or behavioral measures. The purpose of the present review is to highlight the degree of overlap in the assessment of wakefulness and cognition, with consideration of assessment techniques and the underlying neurobiology of both concepts.

DESIGN

Reviews of four key areas were conducted: commonly used techniques in the assessment of wakefulness; neurobiology of sleep/wake and cognition; targets of wake promoting and/or cognition enhancing drugs; and ongoing clinical trials investigating wake promoting effects.

RESULTS

There is clear overlap between the assessment of wakefulness and cognition. There are common techniques which may be used to assess both concepts; aspects of the neurobiology of both concepts may be closely related; and wake-promoting drugs may have nootropic properties (and vice versa). Clinical trials of wake-promoting drugs often, though not routinely, assess aspects of cognition.

CONCLUSIONS

Routine and broad assessment of cognition in the development of wake-promoting drugs may reveal important nootropic effects, which are not secondary to alertness/wakefulness, whilst existing cognitive enhancers may have underexplored or unknown wake promoting properties.

Potential therapeutic interest of adenosine A2A receptors in psychiatric disorders

The interest on targeting adenosine A(2A) receptors in the realm of psychiatric diseases first arose based on their tight physical and functional interaction with dopamine D(2) receptors. However, the role of central A(2A) receptors is now viewed as much broader than just controlling D(2) receptor function. Thus, there is currently a major interest in the ability of A(2A) receptors to control synaptic plasticity at glutamatergic synapses. This is due to a combined ability of A(2A) receptors to facilitate the release of glutamate and the activation of NMDA receptors. Therefore, A(2A) receptors are now conceived as a normalizing device promoting adequate adaptive responses in neuronal circuits, a role similar to that fulfilled, in essence, by dopamine. This makes A(2A) receptors particularly attractive targets to manage psychiatric disorders since adenosine may act as go-between glutamate and dopamine, two of the key players in mood processing. Furthermore, A(2A) receptors also control glia function and brain metabolic adaptation, two other emerging mechanisms to understand abnormal processing of mood, and A(2A) receptors are important players in controlling the demise of neurodegeneration, considered an amplificatory loop in psychiatric disorders. Current data only provide an indirect confirmation of this putative role of A(2A) receptors, based on the effects of caffeine (an antagonist of both A(1) and A(2A) receptors) in psychiatric disorders. However, the introduction of A(2A) receptors antagonists in clinics as anti-parkinsonian agents is hoped to bolster our knowledge on the role of A(2A) receptors in mood disorders in the near future.

Caffeine facilitation of glutamate release from rat cerebral cortex nerve terminals (synaptosomes) through activation protein kinase C pathway: an interaction with presynaptic adenosine A1 receptors

The present study used nerve terminals (synaptosomes) isolated from rat cerebral cortex to investigate the relationship between caffeine and 4-aminopyridine (4AP)-evoked endogenous excitatory neurotransmitter glutamate release. Micromolar concentrations of caffeine facilitated 4AP, but not KCl or ionomycin-evoked glutamate release from synaptosomes. This release facilitation resulted from an enhancement of vesicular and nonvesicular release and associated with an increase both in 4AP-evoked depolarization of the synaptosomal plasma membrane potential and in 4AP-evoked increase in the cytoplasmic free Ca(2+) concentration ([Ca(2+)](C)). In addition, the release facilitation by caffeine was significantly reduced in synaptosomes pretreated with a wide spectrum blocker of N- and P/Q-type Ca(2+) channels, omega-conotoxin MVIIC. Furthermore, protein kinase C (PKC) activator and inhibitor, respectively, superseding or suppressing the caffeine-mediated facilitation of glutamate release. These results concluded that caffeine exerts their presynaptic facilitatory effect, likely through the activation of PKC pathway, which subsequently enhances terminal excitability and Ca(2+) entry to cause an increase in evoked glutamate release from rat cerebrocortical nerve terminals. Additionally, this release facilitation may involve an interaction of caffeine with presynaptic adenosine A1 receptors as adenosine A1 receptor inhibition abolished the caffeine-mediated facilitation of evoked glutamate release.

Differential responsiveness to caffeine and perceived effects of caffeine in moderate and high regular caffeine consumers

RATIONALE

Individual differences in responsiveness to caffeine occur even within a caffeine-consuming population, but the factors that mediate differential responsiveness remain unclear.

OBJECTIVES

To compare caffeine's effects on performance and mood in a group of high vs moderate consumers of caffeine and to examine the potential role of subjective awareness of the effects of caffeine in mediating any differential responsiveness.

MATERIALS AND METHODS

Two groups of regular caffeine consumers (<200 mg/day and >200 mg/day) attended two sessions at which mood and cognitive functions were measured before and 30 min after consumption of 400-mg caffeine or placebo in a capsule. Cognitive tests included visual information processing, match-to-sample visual search (MTS) and simple and choice reaction times. Post-session questionnaires asked participants to describe any perceived effect of capsule consumption.

RESULTS

High consumers, but not moderate consumers, demonstrated significantly faster simple and choice reaction times after caffeine relative to placebo. These effects were not attributable to obvious group differences in withdrawal or tolerance because there were no group differences in baseline mood or in reports of negative affect after caffeine. Instead, the high consumers were more likely to report experiencing positive effects of caffeine, whereas the moderate consumers were more likely to report no effect.

CONCLUSIONS

The sensitivity of caffeine consumers to the mood- and performance-enhancing effects of caffeine is related to their levels of habitual intake. High caffeine consumers are more likely than moderate consumers to perceive broadly positive effects of caffeine, and this may contribute to their levels of use.

A combination of caffeine and taurine has no effect on short term memory but induces changes in heart rate and mean arterial blood pressure

Red Bull energy drink has become extraordinarily popular amongst college students for use as a study aid. We investigated the combined effects of Red Bull's two active ingredients, caffeine and taurine, on short term memory. Studies on the effects of these two neuromodulators on memory have yielded mixed results, and their combined actions have not yet been investigated. In this double-blind study, college student subjects consumed either caffeine and taurine pills or a placebo and then completed a memory assessment. Heart rate and blood pressure were monitored throughout the testing period. The combination of caffeine and taurine had no effect on short term memory, but did cause a significant decline in heart rate and an increase in mean arterial blood pressure. The heart rate decline may have been caused by pressure-induced bradycardia that was triggered by caffeine ingestion and perhaps enhanced by the actions of taurine.

Acute effects of caffeine in volunteers with different patterns of regular consumption

RATIONALE

The effects of caffeine on mood and performance are well established. One explanation of these effects is that caffeine removes negative effects induced by prior caffeine withdrawal. This was tested here by comparing effects of caffeine in withdrawn consumers and non-consumers (who by definition were not withdrawn).

OBJECTIVES

The present study aimed to determine whether caffeine withdrawal influenced mood and performance by comparing regular consumers who had been withdrawn from caffeine overnight with non-consumers. Following this the effects of acute caffeine challenges were compared in withdrawn consumers and non-consumers. In addition, comparisons were made between those with higher and lower caffeine consumption.

METHODS

One hundred seventy-six volunteers participated in the study. Regular caffeine consumption was assessed by questionnaire and this showed that 56 of the sample did not regularly consume caffeinated beverages. Volunteers were instructed to abstain from caffeine overnight and then completed a baseline session measuring mood and a range of cognitive functions at 08.00 the next day. Following this approximately half of the volunteers were given 1 mg/kg caffeine in a milkshake or water (in the 'no caffeine' condition they were given just the milkshake or water) and the test battery repeated one hour later. A second test battery was carried out at 12.00 and a second caffeine challenge at 13.00. A final test session was carried out at 15.00.

RESULTS

The baseline data revealed little evidence of effects of caffeine withdrawal on performance and mood. In contrast to this, caffeine produced a number of significant improvements in performance. There were some differences in the effects of caffeine on regular and non-consumers, with caffeine tending to reduce reaction time in regular consumers while the opposite was true for non-consumers.

CONCLUSIONS

The present results show little evidence of effects of caffeine withdrawal on performance. In contrast, caffeine challenge produced improvements in aspects of performance and these were often not modified by regular caffeine consumption patterns. The differences in effects of caffeine that were observed between non-consumers and regular consumers were in functions that were unaffected by caffeine withdrawal. These findings show that the observed beneficial effects of caffeine cannot be interpreted in terms of a reversal of caffeine withdrawal.

Green tea consumption in everyday life and mental health

OBJECTIVE

Green tea has been widely acknowledged in Japan to induce a pleasurable mental feeling. Recent laboratory studies have suggested positive psychological effects as a result of consuming green tea. The present study examined whether green tea consumption in everyday life in Japan is associated with positive mental health.

DESIGN

A cross-sectional study was performed in February-March 2002.

SETTING AND SUBJECTS

The subjects of the study consisted of a general population of 600 Japanese aged 20-69 years. Responses of 380 subjects, obtained by home-visit interview, were analysed. The questionnaire inquired about consumption of brewed green tea and other beverages, perceived mental health status, lifestyle and others. The 12-item General Health Questionnaire (GHQ 12) was used for the assessment of mental ill-health (GHQ score >or=4).

RESULTS

After adjustments for age, area, perceived mental stress, lifestyle and daily caffeine intake, the consumption of brewed green tea was not statistically associated with any decrease in risk of mental ill-health among either males or females (odds ratio (OR)=0.78, 95% confidence interval (CI)=0.47-1.29 for males; OR=0.77, 95% CI=0.51-1.14 for females). Daily caffeine intake (100 mg) inclusive of green tea, black tea, coffee and other caffeine-containing beverages was associated with a higher risk of mental ill-health among females (OR=1.26, 95% CI=1.01-1.56).

CONCLUSIONS

The results provide population-based evidence on the consumption of brewed green tea in everyday life and mental health, together with information on consumption patterns of various beverages and lifestyles.