caffeine - Mental Alertness

Mental Alertness

Low-dose repeated caffeine administration for circadian-phase-dependent performance degradation during extended wakefulness. Wyatt JK, Cajochen C, Ritz-De Cecco A, Czeisler CA, Dijk DJ. Sleep. 2004 May 1;27(3):374-81.          

Division of Sleep Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA.

OBJECTIVE: To investigate whether the effectiveness of a novel high-frequency low-dose caffeine regimen in counteracting the deterioration of performance during extended wakefulness is related to its interaction with homeostatic or circadian signals modulating performance and sleep propensity. DESIGN: Double-blind, placebo-controlled, parallel-group design in a 29-day forced desynchrony paradigm in which the period of the sleep-wake cycle was scheduled to be 42.85 hours, i.e., far removed from the circadian range. This design allowed for separate estimation of the sleep homeostatic, circadian, and caffeine contributions to performance deficits or improvements. SETTING: Private suite of a general clinical research center, in the absence of time of day information. PARTICIPANTS: Sixteen healthy normal-sleeping men (aged 18-30 years) INTERVENTIONS: Caffeine (0.3 mg per kg per hour) or placebo was administered hourly during the 28.57-hour wake episodes. RESULTS: Plasma caffeine concentrations rose in an exponential saturating manner during wakefulness. Rising caffeine levels markedly attenuated wake-dependent deterioration of a number of measures of cognitive performance, particularly at the circadian performance nadir. Moreover, caffeine enhanced the ability of subjects to remain consistently awake for extended periods, holding subjects back from completing the full transition to sleep, but at the expense of increasing subjective sleepiness. CONCLUSIONS: High-frequency low-dose caffeine administration is effective in countering the detrimental performance effects of extended wakefulness. These data are in accordance with the hypothesis that adenosine is a mediator of performance decrements associated with extended wakefulness and may lead to new strategies to use caffeine in situations in which neurobehavioral functioning is affected by sleep loss.

Caffeine strengthens action monitoring: evidence from the error-related negativity.

Tieges Z, Richard Ridderinkhof K, Snel J, Kok A. Brain Res Cogn Brain Res. 2004 Sep;21(1):87-93.

Department of Psychology, University of Amsterdam, The Netherlands.

The medial frontal cortex, especially the anterior cingulate cortex (ACC), is involved in action monitoring. We studied the role of moderate amounts of caffeine in action monitoring as expressed by the error-related negativity (ERN), an event-related brain component that reflects ACC activity. In a double-blind, placebo-controlled, within-subjects experiment, two caffeine doses (3 and 5 mg/kg body weight) and a placebo were administered to habitual coffee drinkers. Compared with placebo, both caffeine doses enlarged the ERN. Amplitudes of the P2 and P3 components were not affected by caffeine. Thus, the enlarged ERN after caffeine reflects a specific effect on action monitoring. We conclude that consumption of a few cups of coffee strengthens central information processing, specifically the monitoring of ongoing cognitive processes for signs of erroneous outcomes. Brain areas related to action monitoring such as the ACC presumably mediate these caffeine effects.

Caffeine and central noradrenaline: effects on mood, cognitive performance, eye movements and cardiovascular function. Smith A, Brice C, Nash J, Rich N, Nutt DJ. J Psychopharmacol. 2003 Sep;17(3):283-92.

Centre for Occupational and Health Psychology, School of Psychology, Cardiff University, Cardiff, UK.

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 breakfast and caffeine on performance and mood in the late morning and after lunch. Smith AP, Kendrick AM, Maben AL. Neuropsychobiology. 1992;26(4):198-204.

Health Psychology Research Unit, School of Psychology, University of Wales College of Cardiff, UK.

The aim of the present study was to examine the effects of breakfast and caffeine on performance, mood and cardiovascular functioning in the late morning and after lunch. Forty-eight subjects were tested at 07.45 and subjects then assigned to one of the four conditions formed by combining caffeine and breakfast conditions. Subjects in the caffeine condition were given a dose of 4 mg/kg, the caffeine manipulation being double blind. At 11.15 subjects were given another coffee (subjects remained in the same caffeine condition) and had lunch at 12.30. Performance was examined prior to lunch (11.30) and after lunch (14.00). Effects of breakfast on recognition memory (lower false alarm rate) and logical reasoning (reduced accuracy) were found in the late morning but not after lunch. However, a semantic processing task was performed more slowly by the breakfast group after lunch. Caffeine improved performance on a sustained attention task, the logical reasoning task and semantic memory task. Subjects given caffeine also reported greater alertness and feelings of well-being, whereas the effects of breakfast on mood changed from the late morning to early afternoon. Few interactions between breakfast and caffeine conditions were obtained.