The influence of caffeine on human EEG under resting conditions and during mental loads

Inter-individual variability in neural response to low doses of LSD

The repeated use of small doses of psychedelics (also referred to as "microdosing") to facilitate benefits in mental health, cognition, and mood is a trending practice. Placebo-controlled studies however have largely failed to demonstrate strong benefits, possibly because of large inter-individual response variability. The current study tested the hypothesis that effects of low doses of LSD on arousal, attention and memory depend on an individual's cognitive state at baseline. Healthy participants (N = 53) were randomly assigned to receive repeated doses of LSD (15 mcg) or placebo on 4 occasions divided over 2 weeks. Each treatment condition also consisted of a baseline and a 1-week follow-up visit. Neurophysiological measures of arousal (resting state EEG), pre-attentive processing (auditory oddball task), and perceptual learning and memory (visual long-term potentiation (LTP) paradigm) were assessed at baseline, dosing session 1 and 4, and follow-up. LSD produced stimulatory effects as reflected by a reduction in resting state EEG delta, theta, and alpha power, and enhanced pre-attentive processing during the acute dosing sessions. LSD also blunted the induction of LTP on dosing session 4. Stimulatory effects of LSD were strongest in individuals with low arousal and attention at baseline, while inhibitory effects were strongest in high memory performers at baseline. Decrements in delta EEG power and enhanced pre-attentive processing in the LSD treatment condition were still present during the 1-week follow-up. The current study demonstrates across three cognitive domains, that acute responses to low doses of LSD depend on the baseline state and provides some support for LSD induced neuroadaptations that sustain beyond treatment.

Screening for Mild Cognitive Impairment with Speech Interaction Based on Virtual Reality and Wearable Devices

Significant advances in sensor technology and virtual reality (VR) offer new possibilities for early and effective detection of mild cognitive impairment (MCI), and this wealth of data can improve the early detection and monitoring of patients. In this study, we proposed a non-invasive and effective MCI detection protocol based on electroencephalogram (EEG), speech, and digitized cognitive parameters. The EEG data, speech data, and digitized cognitive parameters of 86 participants (44 MCI patients and 42 healthy individuals) were monitored using a wearable EEG device and a VR device during the resting state and task (the VR-based language task we designed). Regarding the features selected under different modality combinations for all language tasks, we performed leave-one-out cross-validation for them using four different classifiers. We then compared the classification performance under multimodal data fusion using features from a single language task, features from all tasks, and using a weighted voting strategy, respectively. The experimental results showed that the collaborative screening of multimodal data yielded the highest classification performance compared to single-modal features. Among them, the SVM classifier using the RBF kernel obtained the best classification results with an accuracy of 87%. The overall classification performance was further improved using a weighted voting strategy with an accuracy of 89.8%, indicating that our proposed method can tap into the cognitive changes of MCI patients. The MCI detection scheme based on EEG, speech, and digital cognitive parameters proposed in this study provides a new direction and support for effective MCI detection, and suggests that VR and wearable devices will be a promising direction for easy-to-perform and effective MCI detection, offering new possibilities for the exploration of VR technology in the field of language cognition.

Prognostic interictal electroencephalographic biomarkers and models to assess antiseizure medication efficacy for clinical practice: A scoping review

Antiseizure medication (ASM) is the primary treatment for epilepsy. In clinical practice, methods to assess ASM efficacy (predict seizure freedom or seizure reduction), during any phase of the drug treatment lifecycle, are limited. This scoping review identifies and appraises prognostic electroencephalographic (EEG) biomarkers and prognostic models that use EEG features, which are associated with seizure outcomes following ASM initiation, dose adjustment, or withdrawal. We also aim to summarize the population and context in which these biomarkers and models were identified and described, to understand how they could be used in clinical practice. Between January 2021 and October 2022, four databases, references, and citations were systematically searched for ASM studies investigating changes to interictal EEG or prognostic models using EEG features and seizure outcomes. Study bias was appraised using modified Quality in Prognosis Studies criteria. Results were synthesized into a qualitative review. Of 875 studies identified, 93 were included. Biomarkers identified were classed as qualitative (visually identified by wave morphology) or quantitative. Qualitative biomarkers include identifying hypsarrhythmia, centrotemporal spikes, interictal epileptiform discharges (IED), classifying the EEG as normal/abnormal/epileptiform, and photoparoxysmal response. Quantitative biomarkers were statistics applied to IED, high-frequency activity, frequency band power, current source density estimates, pairwise statistical interdependence between EEG channels, and measures of complexity. Prognostic models using EEG features were Cox proportional hazards models and machine learning models. There is promise that some quantitative EEG biomarkers could be used to assess ASM efficacy, but further research is required. There is insufficient evidence to conclude any specific biomarker can be used for a particular population or context to prognosticate ASM efficacy. We identified a potential battery of prognostic EEG biomarkers, which could be combined with prognostic models to assess ASM efficacy. However, many confounders need to be addressed for translation into clinical practice.

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.

Stress Classification Using Brain Signals Based on LSTM Network

The early diagnosis of stress symptoms is essential for preventing various mental disorder such as depression. Electroencephalography (EEG) signals are frequently employed in stress detection research and are both inexpensive and noninvasive modality. This paper proposes a stress classification system by utilizing an EEG signal. EEG signals from thirty-five volunteers were analysed which were acquired using four EEG sensors using a commercially available 4-electrode Muse EEG headband. Four movie clips were chosen as stress elicitation material. Two clips were selected to induce stress as it contains emotionally inductive scenes. The other two clips were chosen that do not induce stress as it has many comedy scenes. The recorded signals were then used to build the stress classification model. We compared the Multilayer Perceptron (MLP) and Long Short-Term Memory (LSTM) for classifying stress and nonstress group. The maximum classification accuracy of 93.17% was achieved using two-layer LSTM architecture.

Neurofeedback Therapy for Sensory Over-Responsiveness-A Feasibility Study

Background: Difficulty in modulating multisensory input, specifically the sensory over-responsive (SOR) type, is linked to pain hypersensitivity and anxiety, impacting daily function and quality of life in children and adults. Reduced cortical activity recorded under resting state has been reported, suggestive of neuromodulation as a potential therapeutic modality. This feasibility study aimed to explore neurofeedback intervention in SOR. Methods: Healthy women with SOR (n = 10) underwent an experimental feasibility study comprising four measurement time points (T1—baseline; T2—preintervention; T3—postintervention; T4—follow-up). Outcome measures included resting-state EEG recording, in addition to behavioral assessments of life satisfaction, attaining functional goals, pain sensitivity, and anxiety. Intervention targeted the upregulation of alpha oscillatory power over ten sessions. Results: No changes were detected in all measures between T1 and T2. Exploring the changes in brain activity between T2 and T4 revealed power enhancement in delta, theta, beta, and gamma oscillatory bands, detected in the frontal region (p = 0.03−<0.001; Cohen’s d = 0.637−1.126) but not in alpha oscillations. Furthermore, a large effect was found in enhancing life satisfaction and goal attainment (Cohen’s d = 1.18; 1.04, respectively), and reduced pain sensitivity and anxiety trait (Cohen’s d = 0.70). Conclusion: This is the first study demonstrating the feasibility of neurofeedback intervention in SOR.

Modulation of attention and stress with arousal: The mental and physical effects of riding a motorcycle

Existing theories suggest that moderate arousal improves selective attention, as would be expected in the context of competitive sports or sensation-seeking activities. Here we investigated how riding a motorcycle, an attention-demanding physical activity, affects sensory processing. To do so, we implemented the passive auditory oddball paradigm and measured the EEG response of participants as they rode a motorcycle, drove a car, and sat at rest. Specifically, we measured the N1 and mismatch negativity to auditory tones, as well as alpha power during periods of no tones. We investigated whether riding and driving modulated non-CNS metrics including heart rate and concentrations of the hormones epinephrine, cortisol, DHEA-S, and testosterone. While participants were riding, we found a decrease in N1 amplitude, increase in mismatch negativity, and decrease in relative alpha power, together suggesting enhancement of sensory processing and visual attention. Riding increased epinephrine levels, increased heart rate, and decreased the ratio of cortisol to DHEA-S. Together, these results suggest that riding increases focus, heightens the brain's passive monitoring of changes in the sensory environment, and alters HPA axis response. More generally, our findings suggest that selective attention and sensory monitoring seem to be separable neural processes.

Effects of RF-EMF on the Human Resting-State EEG-the Inconsistencies in the Consistency. Part 1: Non-Exposure-Related Limitations of Comparability Between Studies

The results of studies on possible effects of radiofrequency electromagnetic fields (RF-EMFs) on human waking electroencephalography (EEG) have been quite heterogeneous. In the majority of studies, changes in the alpha-frequency range in subjects who were exposed to different signals of mobile phone-related EMF sources were observed, whereas other studies did not report any effects. In this review, possible reasons for these inconsistencies are presented and recommendations for future waking EEG studies are made. The physiological basis of underlying brain activity, and the technical requirements and framework conditions for conducting and analyzing the human resting-state EEG are discussed. Peer-reviewed articles on possible effects of EMF on waking EEG were evaluated with regard to non-exposure-related confounding factors. Recommendations derived from international guidelines on the analysis and reporting of findings are proposed to achieve comparability in future studies. In total, 22 peer-reviewed studies on possible RF-EMF effects on human resting-state EEG were analyzed. EEG power in the alpha frequency range was reported to be increased in 10, decreased in four, and not affected in eight studies. All reviewed studies differ in several ways in terms of the methodologies applied, which might contribute to different results and conclusions about the impact of EMF on human resting-state EEG. A discussion of various study protocols and different outcome parameters prevents a scientifically sound statement on the impact of RF-EMF on human brain activity in resting-state EEG. Further studies which apply comparable, standardized study protocols are recommended. Bioelectromagnetics. 2019;40:291-318. © 2019 The Authors. Bioelectromagnetics Published by Wiley Periodicals, Inc.

Mapping the pharmacological modulation of brain oxygen metabolism: The effects of caffeine on absolute CMRO2 measured using dual calibrated fMRI

This study aims to map the acute effects of caffeine ingestion on grey matter oxygen metabolism and haemodynamics with a novel MRI method. Sixteen healthy caffeine consumers (8 males, age=24.7±5.1) were recruited to this randomised, double-blind, placebo-controlled study. Each participant was scanned on two days before and after the delivery of an oral caffeine (250mg) or placebo capsule. Our measurements were obtained with a newly proposed estimation approach applied to data from a dual calibration fMRI experiment that uses hypercapnia and hyperoxia to modulate brain blood flow and oxygenation. Estimates were based on a forward model that describes analytically the contributions of cerebral blood flow (CBF) and of the measured end-tidal partial pressures of CO2 and O2 to the acquired dual-echo GRE signal. The method allows the estimation of grey matter maps of: oxygen extraction fraction (OEF), CBF, CBF-related cerebrovascular reactivity (CVR) and cerebral metabolic rate of oxygen consumption (CMRO2). Other estimates from a multi inversion time ASL acquisition (mTI-ASL), salivary samples of the caffeine concentration and behavioural measurements are also reported. We observed significant differences between caffeine and placebo on average across grey matter, with OEF showing an increase of 15.6% (SEM±4.9%, p<0.05) with caffeine, while CBF and CMRO2 showed differences of -30.4% (SEM±1.6%, p<0.01) and -18.6% (SEM±2.9%, p<0.01) respectively with caffeine administration. The reduction in oxygen metabolism found is somehow unexpected, but consistent with a hypothesis of decreased energetic demand, supported by previous electrophysiological studies reporting reductions in spectral power with EEG. Moreover the maps of the physiological parameters estimated illustrate the spatial distribution of changes across grey matter enabling us to localise the effects of caffeine with voxel-wise resolution. CBF changes were widespread as reported by previous findings, while changes in OEF were found to be more restricted, leading to unprecedented mapping of significant CMRO2 reductions mainly in frontal gyrus, parietal and occipital lobes. In conclusion, we propose the estimation framework based on our novel forward model with a dual calibrated fMRI experiment as a viable MRI method to map the effects of drugs on brain oxygen metabolism and haemodynamics with voxel-wise resolution.

Default Mode Network alterations in alexithymia: an EEG power spectra and connectivity study

Recent neuroimaging studies have shown that alexithymia is characterized by functional alterations in different brain areas [e.g., posterior cingulate cortex (PCC)], during emotional/social tasks. However, only few data are available about alexithymic cortical networking features during resting state (RS). We have investigated the modifications of electroencephalographic (EEG) power spectra and EEG functional connectivity in the default mode network (DMN) in subjects with alexithymia. Eighteen subjects with alexithymia and eighteen subjects without alexithymia matched for age and gender were enrolled. EEG was recorded during 5 min of RS. EEG analyses were conducted by means of the exact Low Resolution Electric Tomography software (eLORETA). Compared to controls, alexithymic subjects showed a decrease of alpha power in the right PCC. In the connectivity analysis, compared to controls, alexithymic subjects showed a decrease of alpha connectivity between: (i) right anterior cingulate cortex and right PCC, (ii) right frontal lobe and right PCC, and (iii) right parietal lobe and right temporal lobe. Finally, mediation models showed that the association between alexithymia and EEG connectivity values was directed and was not mediated by psychopathology severity. Taken together, our results could reflect the neurophysiological substrate of some core features of alexithymia, such as the impairment in emotional awareness.

Does acute caffeine ingestion alter brain metabolism in young adults?

Caffeine, as the most commonly used stimulant drug, improves vigilance and, in some cases, cognition. However, the exact effect of caffeine on brain activity has not been fully elucidated. Because caffeine has a pronounced vascular effect which is independent of any neural effects, many hemodynamics-based methods such as fMRI cannot be readily applied without a proper calibration. The scope of the present work is two-fold. In Study 1, we used a recently developed MRI technique to examine the time-dependent changes in whole-brain cerebral metabolic rate of oxygen (CMRO2) following the ingestion of 200mg caffeine. It was found that, despite a pronounced decrease in CBF (p<0.001), global CMRO2 did not change significantly. Instead, the oxygen extraction fraction (OEF) was significantly elevated (p=0.002) to fully compensate for the reduced blood supply. Using the whole-brain finding as a reference, we aim to investigate whether there are any regional differences in the brain's response to caffeine. Therefore, in Study 2, we examined regional heterogeneities in CBF changes following the same amount of caffeine ingestion. We found that posterior brain regions such as posterior cingulate cortex and superior temporal regions manifested a slower CBF reduction, whereas anterior brain regions including dorsolateral prefrontal cortex and medial frontal cortex showed a faster rate of decline. These findings have a few possible explanations. One is that caffeine may result in a region-dependent increase or decrease in brain activity, resulting in an unaltered average brain metabolic rate. The other is that caffeine's effect on vasculature may be region-specific. Plausibility of these explanations is discussed in the context of spatial distribution of the adenosine receptors.

Caffeine alters resting-state functional connectivity measured by blood oxygenation level-dependent MRI

This study aimed to investigate the pharmacological effect of caffeine on functional connectivity measured by resting-state blood oxygenation level-dependent (BOLD) MRI in the motor cortex, visual cortex and default mode network (DMN). The protocols and procedures of the study were reviewed and approved by the Institutional Review Board of our institution. On a 3-T clinical MR system, 20 healthy volunteers underwent imaging before and after oral ingestion of a 200-mg over-the-counter caffeine pill (data from three individuals were excluded from further analysis because of excessive motion). The demographics of the remaining participants were as follows: female/male, 8/9; age, 21-35 years; non-habitual caffeine consumers over the past 6 months. Functional connectivity was calculated using the general linear model, assessed in terms of connected area (voxels) and statistical significance (Student t-values), and correlated with changes in regional cerebral blood flow as measured by arterial spin labeling MRI. Per-subject data analysis showed that caffeine decreased functional connectivity in the motor/visual cortices, but its effects on DMN varied among subjects. Correlation analysis of the changes in functional connectivity and regional blood flow suggested that the effect of caffeine on BOLD functional connectivity was predominantly neural (motor/visual cortices) and partly vascular (DMN). Group analysis showed that, after caffeine ingestion, DMN involved more attentional networks, and more extrastriate areas were integrated into the functional connectivity of the visual cortex, which may be associated with the known pharmacological effect of caffeine in elevating alertness. Caffeine consumption should thus be considered in the experimental design and data interpretation of functional connectivity studies using resting-state BOLD MRI.

Brain imaging and human nutrition: which measures to use in intervention studies?

The present review describes brain imaging technologies that can be used to assess the effects of nutritional interventions in human subjects. Specifically, we summarise the biological relevance of their outcome measures, practical use and feasibility, and recommended use in short- and long-term nutritional studies. The brain imaging technologies described consist of MRI, including diffusion tensor imaging, magnetic resonance spectroscopy and functional MRI, as well as electroencephalography/magnetoencephalography, near-IR spectroscopy, positron emission tomography and single-photon emission computerised tomography. In nutritional interventions and across the lifespan, brain imaging can detect macro- and microstructural, functional, electrophysiological and metabolic changes linked to broader functional outcomes, such as cognition. Imaging markers can be considered as specific for one or several brain processes and as surrogate instrumental endpoints that may provide sensitive measures of short- and long-term effects. For the majority of imaging measures, little information is available regarding their correlation with functional endpoints in healthy subjects; therefore, imaging markers generally cannot replace clinical endpoints that reflect the overall capacity of the brain to behaviourally respond to specific situations and stimuli. The principal added value of brain imaging measures for human nutritional intervention studies is their ability to provide unique in vivo information on the working mechanism of an intervention in hypothesis-driven research. Selection of brain imaging techniques and target markers within a given technique should mainly depend on the hypothesis regarding the mechanism of action of the intervention, level (structural, metabolic or functional) and anticipated timescale of the intervention's effects, target population, availability and costs of the techniques.

The amplitude of the resting-state fMRI global signal is related to EEG vigilance measures

In resting-state functional magnetic resonance imaging (fMRI), functional connectivity measures can be influenced by the presence of a strong global component. A widely used pre-processing method for reducing the contribution of this component is global signal regression, in which a global mean time series signal is projected out of the fMRI time series data prior to the computation of connectivity measures. However, the use of global signal regression is controversial because the method can bias the correlation values to have an approximately zero mean and may in some instances create artifactual negative correlations. In addition, while many studies treat the global signal as a non-neural confound that needs to be removed, evidence from electrophysiological and fMRI measures in primates suggests that the global signal may contain significant neural correlates. In this study, we used simultaneously acquired fMRI and electroencephalographic (EEG) measures of resting-state activity to assess the relation between the fMRI global signal and EEG measures of vigilance in humans. We found that the amplitude of the global signal (defined as the standard deviation of the global signal) exhibited a significant negative correlation with EEG vigilance across subjects studied in the eyes-closed condition. In addition, increases in EEG vigilance due to the ingestion of caffeine were significantly associated with both a decrease in global signal amplitude and an increase in the average level of anti-correlation between the default mode network and the task-positive network.

Caffeine-Induced Global Reductions in Resting-State BOLD Connectivity Reflect Widespread Decreases in MEG Connectivity

In resting-state functional magnetic resonance imaging (fMRI), the temporal correlation between spontaneous fluctuations of the blood oxygenation level dependent (BOLD) signal from different brain regions is used to assess functional connectivity. However, because the BOLD signal is an indirect measure of neuronal activity, its complex hemodynamic nature can complicate the interpretation of differences in connectivity that are observed across conditions or subjects. For example, prior studies have shown that caffeine leads to widespread reductions in BOLD connectivity but were not able to determine if neural or vascular factors were primarily responsible for the observed decrease. In this study, we used source-localized magnetoencephalography (MEG) in conjunction with fMRI to further examine the origins of the caffeine-induced changes in BOLD connectivity. We observed widespread and significant (p < 0.01) reductions in both MEG and fMRI connectivity measures, suggesting that decreases in the connectivity of resting-state neuro-electric power fluctuations were primarily responsible for the observed BOLD connectivity changes. The MEG connectivity decreases were most pronounced in the beta band. By demonstrating the similarity in MEG and fMRI based connectivity changes, these results provide evidence for the neural basis of resting-state fMRI networks and further support the potential of MEG as a tool to characterize resting-state connectivity.

Evaluation of brain functional states based on projections of electroencephalographic spectral parameters on 2-dimensional canonical space

Electroencephalographic (EEG) activities reflect the functional state of the brain, but it is difficult to objectively describe functional brain states. Here, we describe two statistical divergence measures, Mahalanobis distance and Hellinger distance of projections to the reference spaces, to evaluate their state-discriminating ability. Last, divergence measures of 30-min segments after caffeine treatment were compared to evaluate the dose- and time-dependent arousal effects of caffeine to the best reference space. EEG was recorded from Sprague-Dawley rats during pre- and post-administration of caffeine. Several two-dimensional reference spaces were constructed from subsets of the normalized 7 relative band powers pooled from the pre-drug period of all recordings for each cortex: two reference spaces from data sets of the frontal and parietal cortex, and four reference spaces from data sets of active wake, slow-wave sleep, paradoxical sleep state, and all states. Sleep-wake states used as test states were plotted onto the reference spaces, and then, two divergence measures were derived to measure state-discriminating ability of each reference space. First, the reference space of the same cortex as test data was better for discriminating test states than another cortical reference space. Second, the one reference space constructed from data of all states was better for discriminating test states than the other reference spaces. Third, divergence measures were well correlated with sleep-wake durations after caffeine administration and showed the temporal trends of caffeine-induced arousal effect. These results suggest that two statistical measures can objectively describe brain functional states and drug-induced states.

Separating neural and vascular effects of caffeine using simultaneous EEG-FMRI: differential effects of caffeine on cognitive and sensorimotor brain responses

The effects of caffeine are mediated through its non-selective antagonistic effects on adenosine A(1) and A(2A) adenosine receptors resulting in increased neuronal activity but also vasoconstriction in the brain. Caffeine, therefore, can modify BOLD FMRI signal responses through both its neural and its vascular effects depending on receptor distributions in different brain regions. In this study we aim to distinguish neural and vascular influences of a single dose of caffeine in measurements of task-related brain activity using simultaneous EEG-FMRI. We chose to compare low-level visual and motor (paced finger tapping) tasks with a cognitive (auditory oddball) task, with the expectation that caffeine would differentially affect brain responses in relation to these tasks. To avoid the influence of chronic caffeine intake, we examined the effect of 250 mg of oral caffeine on 14 non and infrequent caffeine consumers in a double-blind placebo-controlled cross-over study. Our results show that the task-related BOLD signal change in visual and primary motor cortex was significantly reduced by caffeine, while the amplitude and latency of visual evoked potentials over occipital cortex remained unaltered. However, during the auditory oddball task (target versus non-target stimuli) caffeine significantly increased the BOLD signal in frontal cortex. Correspondingly, there was also a significant effect of caffeine in reducing the target evoked response potential (P300) latency in the oddball task and this was associated with a positive potential over frontal cortex. Behavioural data showed that caffeine also improved performance in the oddball task with a significantly reduced number of missed responses. Our results are consistent with earlier studies demonstrating altered flow-metabolism coupling after caffeine administration in the context of our observation of a generalised caffeine-induced reduction in cerebral blood flow demonstrated by arterial spin labelling (19% reduction over grey matter). We were able to identify vascular effects and hence altered neurovascular coupling through the alteration of low-level task FMRI responses in the face of a preserved visual evoked potential. However, our data also suggest a cognitive effect of caffeine through its positive effect on the frontal BOLD signal consistent with the shortening of oddball EEG response latency. The combined use of EEG-FMRI is a promising methodology for investigating alterations in brain function in drug and disease studies where neurovascular coupling may be altered on a regional basis.

Anti-correlated networks, global signal regression, and the effects of caffeine in resting-state functional MRI

Resting-state functional connectivity magnetic resonance imaging is proving to be an essential tool for the characterization of functional networks in the brain. Two of the major networks that have been identified are the default mode network (DMN) and the task positive network (TPN). Although prior work indicates that these two networks are anti-correlated, the findings are controversial because the anti-correlations are often found only after the application of a pre-processing step, known as global signal regression, that can produce artifactual anti-correlations. In this paper, we show that, for subjects studied in an eyes-closed rest state, caffeine can significantly enhance the detection of anti-correlations between the DMN and TPN without the need for global signal regression. In line with these findings, we find that caffeine also leads to widespread decreases in connectivity and global signal amplitude. Using a recently introduced geometric model of global signal effects, we demonstrate that these decreases are consistent with the removal of an additive global signal confound. In contrast to the effects observed in the eyes-closed rest state, caffeine did not lead to significant changes in global functional connectivity in the eyes-open rest state.

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.

Cholinergic receptor subtypes and their role in cognition, emotion, and vigilance control: an overview of preclinical and clinical findings

RATIONALE

The cholinergic system has long been linked to cognitive processes. Two main classes of acetylcholine (ACh) receptors exist in the human brain, namely muscarinic and nicotinic receptors, of which several subtypes occur.

OBJECTIVES

This review seeks to provide an overview of previous findings on the influence of cholinergic receptor manipulations on cognition in animals and humans, with particular emphasis on the role of selected cholinergic receptor subtypes. Furthermore, the involvement of these receptor subtypes in the regulation of emotion and brain electrical activity as measured by electroencephalography (EEG) shall be addressed since these domains are considered to be important modulators of cognitive functioning.

RESULTS

In regard to cognition, the muscarinic receptor subtypes have been implicated mainly in memory functions, but have also been linked to attentional processes. The nicotinic α7 receptor subtype is involved in working memory, whereas the α4β2* subtype has been linked to tests of attention. Both muscarinic and nicotinic cholinergic mechanisms play a role in modulating brain electrical activity. Nicotinic receptors have been strongly associated with the modulation of depression and anxiety.

CONCLUSIONS

Cholinergic receptor manipulations have an effect on cognition, emotion, and brain electrical activity as measured by EEG. Changes in cognition can result from direct cholinergic receptor manipulation or from cholinergically induced changes in vigilance or affective state.

Caffeine effects on resting-state arousal in children

From previous work in our laboratory, increases in skin conductance level (SCL), together with global (across-scalp) decreases in electroencephalogram (EEG) alpha power and increases in alpha frequency, are useful indices of arousal increase, and here we sought to identify changes in these indices with caffeine ingestion in children. We explored the effects of a single oral dose of caffeine (80 mg) in a randomised double-blind placebo-controlled repeated-measures cross-over study. Thirty healthy children aged between 8 and 13 years (mean age 10.5 years; 11 females) participated in two sessions, 1 week apart. EEG and SCL from a 3 min eyes-closed epoch, commencing approximately 30 min after ingestion of caffeine or placebo, were examined. Caffeine was associated with increased SCL, and a global reduction in EEG power in the theta and alpha bands, as well as topographically-focused reductions in delta and beta power, and a focal increase in alpha frequency. Only global alpha level demonstrated the expected inverse relationship with SCL in both placebo and caffeine conditions. These results are generally consistent with recent electrodermal and EEG studies of arousal. Together with our previous adult data, they indicate that caffeine can be used to increase arousal in both adults and children, without the potential confounds associated with varying task demands. Caffeine appears useful as a simple tool for manipulating arousal in studies exploring its role in physiological and behavioural functioning. This may be helpful in determining the role of hypothetical arousal anomalies in syndromes such as attention-deficit/hyperactivity disorder.

Caffeine reduces resting-state BOLD functional connectivity in the motor cortex

In resting-state functional magnetic resonance imaging (fMRI), correlations between spontaneous low-frequency fluctuations in the blood oxygenation level dependent (BOLD) signal are used to assess functional connectivity between different brain regions. Changes in resting-state BOLD connectivity measures are typically interpreted as changes in coherent neural activity across spatially distinct brain regions. However, this interpretation can be complicated by the complex dependence of the BOLD signal on both neural and vascular factors. For example, prior studies have shown that vasoactive agents that alter baseline cerebral blood flow, such as caffeine and carbon dioxide, can significantly alter the amplitude and dynamics of the task-related BOLD response. In this study, we examined the effect of caffeine (200 mg dose) on resting-state BOLD connectivity in the motor cortex across a sample of healthy young subjects (N=9). We found that caffeine significantly (p<0.05) reduced measures of resting-state BOLD connectivity in the motor cortex. Baseline cerebral blood flow and spectral energy in the low-frequency BOLD fluctuations were also significantly decreased by caffeine. These results suggest that caffeine usage should be carefully considered in the design and interpretation of resting-state BOLD fMRI studies.

Comparing the benefits of caffeine, naps and placebo on verbal, motor and perceptual memory

Caffeine, the world's most common psychoactive substance, is used by approximately 90% of North Americans everyday. Little is known, however, about its benefits for memory. Napping has been shown to increase alertness and promote learning on some memory tasks. We directly compared caffeine (200mg) with napping (60-90min) and placebo on three distinct memory processes: declarative verbal memory, procedural motor skills, and perceptual learning. In the verbal task, recall and recognition for unassociated words were tested after a 7h retention period (with a between-session nap or drug intervention). A second, different, word list was administered post-intervention and memory was tested after a 20min retention period. The non-declarative tasks (finger tapping task (FTT) and texture discrimination task (TDT)) were trained before the intervention and then retested afterwards. Naps enhanced recall of words after a 7h and 20min retention interval relative to both caffeine and placebo. Caffeine significantly impaired motor learning compared to placebo and naps. Napping produced robust perceptual learning compared with placebo; however, naps and caffeine were not significantly different. These findings provide evidence of the limited benefits of caffeine for memory improvement compared with napping. We hypothesize that impairment from caffeine may be restricted to tasks that contain explicit information; whereas strictly implicit learning is less compromised.

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 attenuates waking and sleep electroencephalographic markers of sleep homeostasis in humans

Prolonged wakefulness increases electroencephalogram (EEG) low-frequency activity (< 10 Hz) in waking and sleep, and reduces spindle frequency activity (approximately 12-16 Hz) in non-rapid-eye-movement (nonREM) sleep. These physiologic markers of enhanced sleep propensity reflect a sleep-wake-dependent process referred to as sleep homeostasis. We hypothesized that caffeine, an adenosine receptor antagonist, reduces the increase of sleep propensity during waking. To test this hypothesis, we compared the effects of caffeine and placebo on EEG power spectra during and after 40 h of wakefulness. A total of 12 young men underwent two periods of sleep deprivation. According to a randomized, double-blind, crossover design, they received two doses of caffeine (200 mg) or placebo after 11 and 23 h of wakefulness. Sleep propensity was estimated at 3-h intervals by measuring subjective sleepiness and EEG theta (5-8 Hz) activity, and polysomnographic recordings of baseline and recovery nights. Saliva caffeine concentration decreased from 15.7 micromol/l 16 h before the recovery night, to 1.8 micromol/l 1 h before the recovery night. Compared with placebo, caffeine reduced sleepiness and theta activity during wakefulness. Compared with sleep under baseline conditions, sleep deprivation increased 0.75-8.0 Hz activity and reduced spindle frequency activity in nonREM sleep of the recovery nights. Although caffeine approached undetectable saliva concentrations before recovery sleep, it significantly reduced EEG power in the 0.75-2.0 Hz band and enhanced power in the 11.25-20.0 Hz range relative to placebo. These findings suggest that caffeine attenuated the build-up of sleep propensity associated with wakefulness, and support an important role of adenosine and adenosine receptors in the homeostatic regulation of sleep.

Evidence from the waking electroencephalogram that short sleepers live under higher homeostatic sleep pressure than long sleepers

We used the waking electroencephalogram to study the homeostatic sleep regulatory process in human short sleepers and long sleepers. After sleeping according to their habitual schedule, nine short sleepers (sleep duration < 6 h) and eight long sleepers (> 9 h) were recorded half-hourly during approximately 40 h of wakefulness in a constant routine protocol. Within the frequency range of 0.25-20.0 Hz, spectral power density in the 5.25-9.0 and 17.25-18.0 Hz ranges was higher in short sleepers than in long sleepers. In both groups, increasing time awake was associated with an increase of theta/low-frequency alpha activity (5.25-9.0 Hz), whose kinetics followed a saturating exponential function. The time constant did not differ between groups and was similar to the previously obtained time constant of the wake-dependent increase of slow-wave activity (0.75-4.5 Hz) in the sleep electroencephalogram. In addition, the time constant of the decrease of slow-wave activity during extended recovery sleep following the constant routine did not differ between groups. However, short sleepers showed an abiding enhancement of theta/low-frequency alpha activity during wakefulness after recovery sleep that was independent of the homeostatic process. It is concluded that, while the kinetics of the homeostatic process do not differ between the two groups, short sleepers live under and tolerate higher homeostatic sleep pressure than long sleepers. The homeostat-independent enhancement of theta/low-frequency alpha activity in the waking electroencephalogram in the short sleepers may be genetically determined or be the result of long-term adaptation to chronically short sleep.

Diurnal variation in the quantitative EEG in healthy adult volunteers

AIMS

To define the change in power in standard waveband frequencies of quantitative cortical electroencephalogram (EEG) data over a 24 h period, in a drug free representative healthy volunteer population.

METHODS

This was an open, non randomised study in which 18 volunteers (9 male and 9 female) were studied on 1 study day, over a 24 h period. Volunteers had a cortical EEG recording taken at 0, 2, 4, 6, 8, 10, 12, 16 and 24 h. Each recording lasted for 6 min (3 min eyes open, 3 min eyes closed). All EEG recordings were taken in a quietened ward environment with the curtains drawn round the bed and the volunteer supine. During the 3 min eyes open, volunteers were asked to look at a red circle on a screen at the foot of the bed, and refrain from talking.

RESULTS

Plots produced of geometric mean power by time of the standard wave band frequencies gave some indication of a circadian rhythm over the 24 h period for theta (4. 75-6.75 Hz), alpha1 (7.0-9.5 Hz) and beta1 (12.75-18.50 Hz) wavebands. Mixed models were fitted to both the eyes open and eyes closed data which confirmed a change in mean waveband power with time with statistical significance at the conventional 5% level (P < 0.05).

CONCLUSIONS

These data indicate the presence of a diurnal variation in the cortical quantitative EEG. They support the use of a placebo control group when designing clinical trials which utilize quantitative EEG to screen for central nervous system (CNS) activity of pharmaceutical agents, to control for the confounding variable of time of day at which the EEG recordings were made.

Effects of a new slow release formulation of caffeine on EEG, psychomotor and cognitive functions in sleep-deprived subjects

Caffeine is a widely-consumed psychoactive substance whose stimulant effects on mood, attention and performance are largely recognised. The central nervous system pharmacodynamic profile of a single oral dose of a new slow release (SR) caffeine formulation (600 mg) was assessed in a randomised, double-blind, crossover, placebo-controlled study. Twelve young, health, male, sleep-deprived (for 36 h) subjects were studied using EEG and various measures of psychomotor and cognitive functions, including critical flicker fusion (CFF), choice reaction task (CRT), tracking, continuous performance task (CPT), Stroop test, body sway and subjective evaluation (Stanford Sleepiness Scale). Caffeine significantly ( < 0/05) antagonised the detrimental effects of sleep-deprivation on EEG (i.e. produced a significant decrease in delta and theta relative power and a significant increase in alpha and beta (12-40 Hz) relative power) and psychomotor performance (significant increase in speed of reaction on the CRT and Stroop tests, significant decrease in body sway, significant increase in accuracy of the CPT and significant reduction in subjective sedation) compared to placebo. The effect peaked 4 h after dosing and was maintained until the end of sleep deprivation (i.e. 24 h after dosing). In conclusion, the present results demonstrate that a single dose of caffeine SR possesses alerting effects which are able to reverse the deleterious effect of 36 h sleep deprivation for at least 24 h. Copyright 2000 John Wiley & Sons, Ltd.

Two circadian rhythms in the human electroencephalogram during wakefulness

The influence of the circadian pacemaker and of the duration of time awake on the electroencephalogram (EEG) was investigated in 19 humans during approximately 40 h of sustained wakefulness. Two circadian rhythms in spectral power density were educed. The first rhythm was centered in the theta band (4.25-8.0 Hz) and exhibited a minimum approximately 1 h after the onset of melatonin secretion. The second rhythm was centered in the high-frequency alpha band (10.25-13.0 Hz) and exhibited a minimum close to the body temperature minimum. The latter rhythm showed a close temporal association with the rhythms in subjective alertness, plasma melatonin, and body temperature. In addition, increasing time awake was associated with an increase of power density in the 0.25- to 9.0-Hz and 13.25- to 20. 0-Hz ranges. It is concluded that the waking EEG undergoes changes that can be attributed to circadian and homeostatic (i.e., sleep-wake dependent) processes. The distinct circadian variations of EEG activity in the theta band and in the high-frequency alpha band may represent electrophysiological correlates of different aspects of the circadian rhythm in arousal.

Quantitative topographical electroencephalographic analysis after intravenous clonidine in healthy male volunteers

We used quantitative topographical electroencephalography (EEG) to determine the time course of changes in brain electrical activity after clonidine infusion. Twenty healthy male volunteers (aged 24 +/- 5 yr) were included in the randomized, double-blind, placebo-controlled (Group 1, placebo, n = 10; Group 2, 2.0 micrograms/kg clonidine, n = 10) study. EEG (17 electrodes, common average reference, fast Fourier transformation, band pass 0.4-35.0 Hz) output was recorded until 145 min after drug infusion. Subjects were intermittently stimulated by verbal commands. Clonidine-related changes resulted in attenuation of the physiological alpha fluctuations seen in untreated subjects and were most pronounced at parietooccipital (P4, O2) recording sites. This was associated with initial maximal increases in slow wave activity (delta) almost uniformly distributed over the whole cortex, restricting with time to occipital regions (O2). The EEG mapping technique may provide more specific information about clonidine-mediated sedative effects, indicating facilitations of EEG patterns that are not homogeneously distributed. These EEG changes cannot be explained by physiologic changes in vigilance or by normal sleep stages because they were not observed after placebo. EEG effects seem to be unrelated to changes in hemodynamics.

IMPLICATIONS

In healthy volunteers, placebo-controlled signal changes in the electroencephalogram were evaluated to quantify sedative drug effects after intravenous application of clonidine. A multichannel recording system and electroencephalogram mapping technique indicate fluctuations of electroencephalogram patterns that are not homogeneously distributed over the cortex associated with sedation.

Dose-dependent pharmacokinetics and psychomotor effects of caffeine in humans

Twelve healthy volunteers received oral placebo, 250 mg of caffeine, and 500 mg of caffeine in a randomized, double-blind, single-dose crossover study. Caffeine kinetics were nonlinear, with clearance significantly reduced and elimination half-life prolonged at the 500-mg compared to the 250-mg dose. The lower dose of caffeine produced more favorable subjective effects than the higher dose (elation, peacefulness, pleasantness), whereas unpleasant effects (tension, nervousness, anxiety, excitement, irritability, nausea, palpitations, restlessness) following the 500-mg dose exceeded those of the 250-mg dose. The lower dose of caffeine enhanced performance on the digit symbol substitution test and a tapping speed test compared to placebo; high-dose caffeine produced less performance enhancement than the lower dose. The plasma concentration versus response relationship revealed concentration-dependent increases in anxiety and improvements in cognitive and motor performance at low to intermediate concentrations. Both caffeine doses reduced electroencephalographic amplitude over the 4 Hz to 30 Hz spectrum, as well as in the alpha (8-11 Hz) and beta (12-30 Hz) ranges; however, effects were not dose-dependent. While favorable subjective and performance-enhancing stimulant effects occur at low to intermediate caffeine doses, the unfavorable subjective and somatic effects, as well as performance disruption, from high doses of caffeine may intrinsically limit the doses of caffeine used in the general population.

The effects of different doses of caffeine on habituation of the human acoustic startle reflex

Research in this laboratory showed that caffeine (4 mg/kg) delays habituation of the acoustic startle reflex in humans. The present study examined the effects of 2- and 6-mg/kg doses of caffeine on acoustic startle habituation in moderate-high and low caffeine users. Eyeblink responses to 30 trials of 85-dB noise stimuli were measured beginning 30 min after oral ingestion of either placebo or 2 or 6 mg/kg of caffeine. The 2-mg/kg dose of caffeine delayed startle habituation in both moderate-high and low caffeine users. The 6-mg/kg dose produced no differential effects on startle responding from placebo. In moderate-high users, following habituation, startle responding was smaller in the placebo condition compared to both caffeine conditions. In low users there were no differences in posthabituation responding between doses, suggesting that this dose effect is dependent on a history of chronic caffeine usage.

Electrocortical, autonomic, and subjective responses to rhythmic audio-visual stimulation

The present study was designed to test the hypothesis that varying sensory input can affect mood, autonomic arousal, and electrocortical activity. Twenty right-handed males were exposed to three rhythmic audio-visual stimulation programs, with either a high intensity and variety of stimuli (program H), a low stimulation (program L) or with a transient from high to low (program HL). Multichannel EEG, heart rate, and skin conductance were recorded continuously, and after each trial mood was rated on a bipolar adjective list. EEG data were subjected to FFT dipole approximation procedure, and dipole locations and field strength (Global Field Power) were analyzed for the frequency bands theta, alpha, and beta 1. Mood ratings clearly differed between programs H and HL, with highest values of arousal after H. Programs L and HL decreased autonomic arousal, whereas H induced deactivating as well as activating effects. Field strength of the alpha band decreased similarly during all programs. Dipole sources were located more to the left in the alpha band and more to the right in the beta 1 band during all programs as compared with baseline. Therefore, programs affected mood and autonomic variables differently, but not electrocortical variables. The higher activation of the right hemisphere during all programs is interpreted as an indication that audio-visual stimulation does induce changes in the brain, such as are commonly found in altered states of consciousness.