[Caffeine and EEG mapping: effects of visuo-spatial task in healthy volunteers]

Vigilance and wake EEG architecture in simulated hyperammonaemia: a pilot study on the effects of L-Ornithine-L-Aspartate (LOLA) and caffeine

Hyperammonaemia/mild hepatic encephalopathy (HE) can be simulated by the oral administration of a so-called amino acid challenge (AAC). This study sought to assess the effects of the AAC alone and in combination with either ammonia-lowering [L-ornithine-L-aspartate (LOLA)] or vigilance-enhancing medication (caffeine). Six patients with cirrhosis (5 males; 61.3 ± 9.2 years; 5 Child A, 1 Child B) and six healthy volunteers (5 males; 49.8 ± 10.6 years) were studied between 08:00 and 19:00 on Monday of three consecutive weeks. The following indices were obtained: hourly capillary ammonia, hourly subjective sleepiness, paper & pencil/computerized psychometry and wake electroencephalography (EEG) at 12:00, i.e. at the time of the maximum expected effect of the AAC.

RESULTS

On average, patients had worse neuropsychological performance and slower EEG than healthy volunteers in all conditions but differences did not reach significance. In healthy volunteers, the post-AAC increase in capillary ammonia levels was contained by both the administration of LOLA and of caffeine (significant differences between 10:00 and 14:00 h). The administration of caffeine also resulted in a reduction in subjective sleepiness and in the amplitude of the EEG on several frontal/temporal-occipital sites (p < 0.05; paired t-test). Changes in ammonia levels, subjective sleepiness and the EEG in the three conditions were less obvious in patients. In conclusion, both LOLA and caffeine contained the AAC-induced increase in capillary ammonia, especially in healthy volunteers. Caffeine also counteracted the AAC effects on sleepiness/EEG amplitude. The association of ammonia-lowering and vigilance-enhancing medication in the management of HE is worthy of further study.

Effects of dietary caffeine on topographic EEG after controlling for withdrawal and withdrawal reversal

BACKGROUND/AIMS

Despite several decades of research into the effects of caffeine on EEG, few consistent findings have emerged. Notwithstanding the likelihood that differences in methodology may explain some of the inconsistency, confidence in the published findings is undermined by the failure in previous studies to control for the effects of caffeine withdrawal and withdrawal reversal.

METHODS

Participants (n = 22) alternated weekly between ingesting placebo and caffeine (1.75 mg/kg) 3 times daily for 4 consecutive weeks. EEG activity was measured at 32 sites during eyes closed, eyes open, and performance of a vigilance task.

RESULTS

Caffeine was found to have few and modest effects on EEG in the theta and alpha bandwidths, and no effects in the delta and beta bandwidths. Evidence was found of withdrawal, withdrawal reversal, and tolerance in relation to observed increases in theta power during task performance; withdrawal and withdrawal reversal in relation to increases in alpha power during all three behavioural conditions (eyes closed, eyes open, and task performance), and withdrawal-induced adverse effects in relation to aspects of subjective mood.

CONCLUSION

The finding of similar increases in theta power following caffeine challenge and acute caffeine withdrawal casts doubt on whether caffeine may be viewed as having direct stimulant effects. Results could suggest that change in drug state, whether in the form of acute caffeine withdrawal or challenge, may be disruptive to electrophysiological activity in the brain.

Caffeine, sleep and wakefulness: implications of new understanding about withdrawal reversal

The broad aim of this review is to critically examine the implications of new understanding concerning caffeine withdrawal and withdrawal reversal in the context of research concerned with the effects of caffeine on sleep and wakefulness. A comprehensive search was conducted for relevant experimental studies in the PubMED and PsycINFO databases. Studies were assessed with particular reference to methodological adequacy for controlling against confounding due to caffeine withdrawal and withdrawal reversal. This assessment was used to clarify evidence of effects, highlight areas of ambiguity and derive recommendations for future research. It was found that researchers have generally failed to take account of the fact that habitual use of caffeine, even at moderate levels, leads to physical dependence evidenced by physiological, behavioural and subjective withdrawal effects during periods of abstinence. Consequently, there has been near-complete absence of adequate methodological controls against confounding due to reversal of withdrawal effects when caffeine is experimentally administered. The findings of what has been a substantial research effort to elucidate the effects of caffeine on sleep and wakefulness, undertaken over a period spanning decades, are ambiguous. Current shortcomings can be redressed by incorporating suitable controls in new experimental designs.

An ERD mapping study of the neurocognitive processes involved in the perceptual and semantic analysis of environmental sounds and words

The aim of this paper was to investigate and compare the EEG mechanisms underlying the perceptual and semantic processes involved in environmental and language sounds perception by manipulating the degree of identification of sounds and using the ERD (event-related desynchronization) method in healthy subjects. Four types of stimuli were analyzed: meaningful environmental sounds, meaningless sounds, words and non-words. We report many similarities in the ERDs and ERSs (event-related synchronizations) patterns among all stimuli, with: (i) similar time-course of ERDs and ERSs between meaningful environmental sounds and words, and between meaningless sounds and non-words; (ii) similar topography of the maximal ERDs for meaningful environmental sounds, words and non-words; and (iii) same right posterior ERSs for all four stimuli. However, differences were also observed: (i) in time-course, with earlier ERSs for meaningless than meaningful stimuli, whether environmental or verbal; and (ii) in topography, with ERDs predominating in left and right hemisphere channels for meaningful and meaningless environmental sounds, respectively; (iii) ERSs predominating in the left temporal channel for non-words and in the left posterior and right frontal channels for meaningless sounds. The results of this study suggest that meaningful stimuli involve greater and longer-lasting semantic processes than meaningless stimuli, while the occurrence of ERSs for the latter points to the possible involvement of an inhibitory processing of semantic representations. Finally, the findings concerning the comparison between verbal and non verbal stimuli suggest the involvement of left-lateralized phonological and semantic processes for the former, and more distributed neurocognitive processes in both hemispheres for the latter although with predominant left laterality for their semantic processing.

Effect of environmental sound familiarity on dynamic neural activation/inhibition patterns: an ERD mapping study

The aim of this study was to analyze the timing and topography of brain activity in relation to the cognitive processing of different types of auditory information. We specifically investigated the effects of familiarity on environmental sound identification, an issue which has been little studied with respect to cognitive processes, neural substrates, and time course of brain activity. To address this issue, we implemented and applied an electroencephalographic mapping method named event-related desynchronization, which allows one to assess the dynamics of neuronal activity with high temporal resolution (here, 125 ms); we used 19 recording electrodes with standard positioning. We designed an activation paradigm in which healthy subjects were asked to discriminate binaurally heard sounds belonging to one of two distinct categories, "familiar" (i.e., natural environmental sounds) or "unfamiliar" (i.e., altered environmental sounds). The sounds were selected according to strict preexperimental tests so that the former should engage greater semantic, and the latter greater structural, analysis, which we predicted to preferentially implicate left posterior and right brain regions, respectively. During the stimulations, significant desynchronizations (thought to reflect neuronal activations) were recorded over left hemisphere regions for familiar sounds and right temporofrontal regions for unfamiliar sounds, but with only few significant differences between the two sound categories and a common bilateral activation in the frontal regions. However, strongly significant differences between familiar and unfamiliar sounds occurred near the end of and following the stimulations, due to synchronizations (though to reflect deactivations) which appeared over the left posterior regions, as well as the vertex and bilateral frontal cortex, only after unfamiliar sounds. These unexpected synchronizations after the unfamiliar stimuli may reflect an awareness of the unfamiliarity of such sounds, which may have induced an inhibition of semantic and episodic representations because the latter could not be associated with meaningless sounds.

Topographic EEG activations during timbre and pitch discrimination tasks using musical sounds

Successive auditory stimulation sequences were presented binaurally to 18 young normal volunteers. Five conditions were investigated: two reference tasks, assumed to involve passive listening to couples of musical sounds, and three discrimination tasks, one dealing with pitch, and two with timbre (either with or without the attack). A symmetrical montage of 16 EEG channels was recorded for each subject across the different conditions. Two quantitative parameters of EEG activity were compared among the different sequences within five distinct frequency bands. As compared to a rest (no stimulation) condition, both passive listening conditions led to changes in primary auditory cortex areas. Both discrimination tasks for pitch and timbre led to right hemisphere EEG changes, organized in two poles: an anterior one and a posterior one. After discussing the electrophysiological aspects of this work, these results are interpreted in terms of a network including the right temporal neocortex and the right frontal lobe to maintain the acoustical information in an auditory working memory necessary to carry out the discrimination task.

[EEG recorded after effort in triathletes. Influence of prior inhalation of hyperbaric oxygen]

Quantitative EEG was recorded during 3 sessions, once a week, in 10 high-level amateur triathletes, who regularly competed in triathlon. At each session, the EEG was recorded 15 min after a submaximal exercise test. During the second session, the exercise test came immediately after 30 min of hyperbaric oxygenation (100% oxygen at 2 atmosphere absolute pressure). The others conditions of the EEG recording were the same for the 3 sessions. The purpose of the work was to study the variations of the EEG power spectrum (from 1 to 20 Hz) which occurred between the 3 sessions. Descriptive analysis of the results show, after hyperbaric oxygenation, a diffuse increase of absolute power for several frequencies in the theta, alpha and beta bands.

Inter- and intra-individual probability maps in EEG cartography by use of nonparametric Fisher tests

The three types of non-parametric permutation Fisher tests have been applied to inter-individual group studies and further to intra-individual multiple EEG recording sequences, providing computations of EEG probability maps testing two ordinal hypotheses. Two examples of previous group studies with "EEG local cerebral activation" are given: mental computation in a group of 20 controls and caffeine effects versus placebo in a group of 10 controls. For the intra-individual study, two successive recordings of 2.3 min eyes closed (EC1 and EC2), obtained at 50 min intervals, were compared by paired exact permutation Fisher tests (over 15 or 42 synchronous EEG sequences). These tests were applied to descriptive spectral parameters: RMS and % amplitudes, mean frequencies, resonance coefficient, for raw unfiltered EEG and delta, theta, alpha, alpha 1, alpha 2, beta 1, beta 2 frequency bands. Two hypotheses were tested for each of the computed 31 parameters, providing two probability maps indicating if the parameter was greater or lower in the first EEG recording or in the second. The second EEG sequence, EC2, was "EEG activated" compared to the first sequence EC1 if the following were present: decreased amplitudes mainly in raw EEG, low activity and alpha bands; increased frequencies mainly, in raw EEG, delta and beta 1 fast activities; increased fast activity percentages; decreased coefficient of resonance. The effect of choice of reference was also evaluated: probability maps for a frontal reference were different than other probability maps obtained after computation of average reference or source derivation.(ABSTRACT TRUNCATED AT 250 WORDS)