Eveline A. de Bruin

Scale-free dynamics of global functional connectivity in the human brain

Higher brain functions depend upon the rapid creation and dissolution of ever changing synchronous cell assemblies. We examine the hypothesis that the dynamics of this process displays scale‐free, self‐similar properties. EEGs (19 channels, average reference, sample frequency 500 Hz) of 15 healthy subjects (10 men; mean age 22.5 years) were analyzed during eyes‐closed and eyes‐open no‐task conditions. Mean level of synchronization as a function of time was estimated with the synchronization likelihood for five frequency bands (0.5–4, 4–8, 8–13, 13–30, and 30–48 Hz). Scaling in these time series was investigated with detrended fluctuation analysis (DFA). DFA analysis of global synchronization time series showed scale‐free characteristics, suggesting neuronal dynamics do not necessarily have a characteristic time constant. The scaling exponent as determined with DFA differed significantly for different frequency bands and conditions. The exponent was close to 1.5 for low frequencies (δ, θ, and α) and close to 1 for β and γ bands. Eye opening decreased the exponent, in particular in α and β bands. Fluctuations of EEG synchronization in δ, θ, α, β, and γ bands exhibit scale‐free dynamics in eyes‐closed as well as eyes‐open no‐task states. The decrease in the scaling exponent following eye opening reflects a relative preponderance of rapid fluctuations with respect to slow changes in the mean synchronization level. The existence of scaling suggests that the underlying dynamics may display self‐organized criticality, possibly representing a near‐optimal state for information processing. Hum. Brain Mapping 22:99–111, 2004.

Health Risks of Chronic Moderate and Heavy Alcohol Consumption: How Much Is Too Much?

This article presents the proceedings of a symposium held at the meeting of the International Society for Biomedical Research on Alcoholism (ISBRA) in Mannheim, Germany, in October 2004. Most of what we know about the deleterious effects of alcohol in vivo has been gleaned from studies in sober alcoholics recruited from substance abuse treatment programs. Little is known about effects of chronic drinking in the moderate or heavy range encountered in a much larger fraction of modern society. Extrapolation of information on the adverse effects of chronic drinking on organ function from clinical samples to social drinkers in the general population has to be met with great skepticism, as it may lead to wrong conclusions about the chronic effects of alcohol in social drinkers. Several recent studies suggest that moderate alcohol consumption has certain beneficial health effects, whereas heavy social alcohol consumption has recently been associated with organ abnormalities and cognitive deficits. These social drinking effects have attracted great public interest; reports of benefits of moderate drinking have also inspired inappropriate publications by the media, including misleading advertisements by the alcohol producing and distributing industry. Although adverse effects of moderate to heavy drinking on heart, liver, and cancer development have attracted attention by clinicians and researchers for some time, its compromising effects on brain and cognition have only recently been studied. This symposium brought together researchers from different disciplines, who reviewed and presented new data on consequences of social drinking in the areas of clinical neuropsychology and behavior (Drs. Nixon and Meyerhoff), neurophysiology (Dr. Nixon, Ms. De Bruin), neuroimaging (Ms. de Bruin, Dr. Meyerhoff), hepatic disease (Dr. Bode), and cancer (Dr. Seitz). The symposium aimed to clarify both the potential health benefits of moderate alcohol consumption and risks of moderate and heavy drinking on proper organ function and to provide insights and new data to practicing physicians and public health authorities for education on problem drinking.

L-theanine and caffeine improve task switching but not intersensory attention or subjective alertness.

Tea ingredients L-theanine and caffeine have repeatedly been shown to deliver unique cognitive benefits when consumed in combination. The current randomized, placebo-controlled, double-blind, cross-over study compared a combination of L-theanine (97 mg) and caffeine (40 mg) to a placebo on two attention tasks and a self-report questionnaire before, and 10 and 60 min after consumption. The combination of L-theanine and caffeine significantly improved attention on a switch task as compared to the placebo, while subjective alertness and intersensory attention were not improved significantly. The results support previous evidence that L-theanine and caffeine in combination can improve attention.

Focal brain matter differences associated with lifetime alcohol intake and visual attention in male but not in female non-alcohol-dependent drinkers.

The purpose of this study was to investigate whether current or lifetime alcohol intake is related to focal gray and white matter in healthy non-alcohol-dependent drinkers, and, if so, whether these densities are related to functional brain activity associated with visual attention. Voxel-based morphometric analyses of gray- and white-matter densities, and event-related potentials in response to a visual-attention task were determined in 47 male drinkers (current alcohol intake 20 drinks per week, lifetime alcohol intake 240 kg) and 44 female drinkers (current alcohol intake 15 drinks per week, lifetime alcohol intake 170 kg). All participants had a negative personal and family history of alcohol dependence to reduce possible confounding by genetic factors related to alcohol dependence. In males, mean lifetime alcohol intake was negatively associated with gray-matter density and positively associated with white-matter density in the right frontal gyrus (BA 6) and the right parietal region (BA 40). Right frontal (but not right parietal) gray and white matter in males correlated with the P3 amplitude of the event-related potentials elicited in a visual-attention task. In females, mean lifetime alcohol intake was not associated with gray- or white-matter density. Current alcohol intake was unrelated to gray or white matter in both males and females. In conclusion, lifetime alcohol intake is associated with focal gray-matter decreases and white-matter increases in the right frontal and right parietal brain regions in non-alcohol-dependent males, but not in females. These alcohol-related differences in focal brain matter in males are associated with differences in brain function related to visual attention. As the confounding effects of genetic factors were reduced, the present results may selectively relate to the effects of alcohol intake on focal brain matter.

Associations between alcohol intake and brain volumes in male and female moderate drinkers

BACKGROUND Alcohol-dependent individuals have brain volume loss. Possibly, moderate drinkers who are not alcohol dependent have similar but less prominent brain damage. The authors investigated whether current or lifetime alcohol intake is related to volumes of total brain, cerebellum, ventricles, peripheral cerebrospinal fluid, and cerebral gray and white matter in moderate drinkers. METHODS The relation between current or lifetime alcohol intake and brain volumes of 47 male moderate drinkers (current alcohol intake 20 drinks per week, lifetime alcohol intake 240 kg) and 44 female moderate drinkers (current alcohol intake 15 drinks per week, lifetime alcohol intake 170 kg), all without a personal or family history of alcohol dependence, was determined using high-resolution magnetic resonance images, corrected for intracranial volume, age, and sex. RESULTS In males, mean lifetime alcohol intake was positively associated with cerebral white matter volume, particularly in the frontal region. In females, mean lifetime alcohol intake was not associated with brain volumes. Current alcohol intake was unrelated to brain volumes in either males or females. CONCLUSIONS Neither current nor lifetime alcohol intake is associated with decreases in brain volumes in male or female moderate drinkers. Because all participants had a negative personal and family history of alcohol dependence, the current results relatively purely concern the effects of moderate alcohol intake on brain volumes.

Age-related differences in brain activity during extended continuous word recognition in children

To examine the development of verbal recognition memory in primary-school children, 36 healthy younger children (8-9 years old) and 36 healthy older children (11-12 years old) participated in an ERP study with an extended continuous recognition task. Each word of a series of 30 words was shown randomly for six times interspersed with distracter words. The children were required to make old versus new decisions. The data analyses focused on old/new effects (repetition 1 vs. new word) and multiple repetition effects (repetitions 1 through 5) for the N1, P2, N400, and the late positive complex (LPC, 500-800 ms after stimulus onset). Younger children exhibited a strong P2 multiple repetition effect across left lateral regions, with P2 amplitudes increasing linearly with the number of word repetitions. Compared to younger children, older children exhibited a much stronger N400 old/new effect across parietal regions. Old/new and repetition effects for N1 and LPC were similar in both age groups. Correlational analysis showed that in older children, larger N400 old/new effects on the continuous recognition task were moderately associated with better verbal learning on an auditory verbal learning task. In both age groups, the gain in recognition accuracy over multiple repetitions correlated with the LPC repetition effect. The age differences in P2 repetition effects and N400 old/new effects suggest that in younger children whole-word orthographic representations are dependent on the strength of the memory trace and that lexical-semantic representations develop with age. The LPC results suggest that recollection plays a substantial role in recognition memory of both younger and older children.

Age-related differences in brain electrical activity during extended continuous face recognition in younger children, older children and adults

To examine the development of recognition memory in primary-school children, 36 healthy younger children (8-9 years old) and 36 healthy older children (11-12 years old) participated in an ERP study with an extended continuous face recognition task (Study 1). Each face of a series of 30 faces was shown randomly six times interspersed with distracter faces. The children were required to make old vs. new decisions. Older children responded faster than younger children, but younger children exhibited a steeper decrease in latencies across the five repetitions. Older children exhibited better accuracy for new faces, but there were no age differences in recognition accuracy for repeated faces. For the N2, N400 and late positive complex (LPC), we analyzed the old/new effects (repetition 1 vs. new presentation) and the extended repetition effects (repetitions 1 through 5). Compared to older children, younger children exhibited larger frontocentral N2 and N400 old/new effects. For extended face repetitions, negativity of the N2 and N400 decreased in a linear fashion in both age groups. For the LPC, an ERP component thought to reflect recollection, no significant old/new or extended repetition effects were found. Employing the same face recognition paradigm in 20 adults (Study 2), we found a significant N400 old/new effect at lateral frontal sites and a significant LPC repetition effect at parietal sites, with LPC amplitudes increasing linearly with the number of repetitions. This study clearly demonstrates differential developmental courses for the N400 and LPC pertaining to recognition memory for faces. It is concluded that face recognition in children is mediated by early and probably more automatic than conscious recognition processes. In adults, the LPC extended repetition effect indicates that adult face recognition memory is related to a conscious and graded recollection process rather than to an automatic recognition process.

Chronic effects of social drinking in a card-sorting task: an event related potential study☆

OBJECTIVE The Wisconsin Card Sorting Task (WCST) is one of the most widely used neuropsychological tests of frontal lobe function, which is thought to be affected by regular alcohol use. The present study used a computer-adapted version of the WCST to assess the effects of chronic alcohol consumption on the brain. METHODS Participants (N=59) sorted cards according to an initially unknown sorting rule, which referred to shape, number, or color. The correctness of the chosen sorting rule was indicated by a feedback stimulus. This correct sorting rule had to be followed for a number of stimuli, and when it changed participants had to find out which rule had to be followed next. A distinction was made between early (correct sorting rule is unknown) and late trials (correct sorting rule is known and applied). To measure brain activity related during the task event related potentials (ERPs) were recorded to the target and feedback stimulus in light (N=14), moderate (N=16) and heavy (N=19) social drinkers and excessive alcohol users (N=10). RESULTS No differences in number of series completed or the reaction time in each trial, were found between the four groups. In contrast, a mid-frontal N1 component in reaction to the feedback stimuli did reveal differences between the four groups. In the light and moderate drinkers, on early feedback trials the N1 was larger relative to late feedback trials, but this effect was absent in the heavy social drinkers and excessive drinkers. CONCLUSIONS The reduced N1 effect with increasing alcohol intake could reflect abnormal allocation of attention or impaired conflict monitoring, possibly based on activity in the anterior cingulate cortex. SIGNIFICANCE Heavy social drinking and excessive drinking leads to changes in the mid-frontal N1 during feedback trials of the WCST.

Relationship between carbohydrate-deficient transferrin, gamma-glutamyl transferase, and mean corpuscular volume levels and alcohol-related brain volume decreases in male drinkers.

We investigated the association between mean corpuscular volume (MCV), carbohydrate‐deficient transferrin (CDT), and gamma‐glutamyl transferase (GGT) levels and gray and white brain matter in male drinkers to find out which if any of these biomarkers of alcohol consumption is indicative for alcohol‐related differences in brain volume.

Attention Benefits of Tea and Tea Ingredients: A Review of the Research to Date

Tea consumption has traditionally been associated with mental benefits, often ascribed to caffeine and L-theanine. Research to date suggests that tea improves attention. However, findings subtly differ for tea as a whole and for caffeine or L-theanine. Specifically, tea was found to improve simple attention processes, involving arousal and psychomotor activity, similar to the effects of caffeine. However, tea also improved more complex attention processes (e.g. Switch task performance), by allowing subjects to be more focused on the task at hand. In contrast, caffeine has been shown to affect complex attention performance, but only when consumed in doses higher than those regularly consumed in tea. While behavioral effects of L-theanine are largely absent, caffeine and L-theanine consumed together may exert different effects from those obtained from caffeine alone. Moreover, tea not only improves attention performance but also feelings of alertness. In summary, tea and tea ingredients can improve attention.