Narrow band quantitative and multivariate electroencephalogram analysis of peri-adolescent period

Background

The peri-adolescent period is a crucial developmental moment of transition from childhood to emergent adulthood. The present report analyses the differences in Power Spectrum (PS) of the Electroencephalogram (EEG) between late childhood (24 children between 8 and 13 years old) and young adulthood (24 young adults between 18 and 23 years old).

Results

The narrow band analysis of the Electroencephalogram was computed in the frequency range of 0–20 Hz. The analysis of mean and variance suggested that six frequency ranges presented a different rate of maturation at these ages, namely: low delta, delta-theta, low alpha, high alpha, low beta and high beta. For most of these bands the maturation seems to occur later in anterior sites than posterior sites. Correlational analysis showed a lower pattern of correlation between different frequencies in children than in young adults, suggesting a certain asynchrony in the maturation of different rhythms. The topographical analysis revealed similar topographies of the different rhythms in children and young adults. Principal Component Analysis (PCA) demonstrated the same internal structure for the Electroencephalogram of both age groups. Principal Component Analysis allowed to separate four subcomponents in the alpha range. All these subcomponents peaked at a lower frequency in children than in young adults.

Conclusions

The present approaches complement and solve some of the incertitudes when the classical brain broad rhythm analysis is applied. Children have a higher absolute power than young adults for frequency ranges between 0-20 Hz, the correlation of Power Spectrum (PS) with age and the variance age comparison showed that there are six ranges of frequencies that can distinguish the level of EEG maturation in children and adults. The establishment of maturational order of different frequencies and its possible maturational interdependence would require a complete series including all the different ages.

Abnormal ERPs and high frequency bands power in multiple sclerosis

Event-related potentials (ERPs) and power spectral density (PSD) were registered during an auditory-oddball paradigm in 11 MS patients. These patients showed a decrease in the amplitude of P2 and N2 components and a delayed P3 latency compared to control subjects suggesting that the attentional orienting mechanism in the auditory modality is affected in MS. The PSD analysis showed that MS patients exhibited an increased power in beta and gamma bands. The combined analysis of frequency and time domain suggested diverse phenomena that occurred in the MS patient group related with the EEG background or the motivational status.

Location of brain rhythms and their modulation by preparatory attention estimated by current density

To test the hypothesis that there is a functional modulation of conventional EEG bands associated with preparatory attention, putative changes in the spontaneous brain rhythms and their associated cerebral sources were addressed. The goals of the present report were, first, to find the brain areas with maximal rhythmic activity before warning and imperative stimuli in a classic contingent negative variation (CNV) paradigm, and, second, to study the modulation of the EEG rhythms of these areas during the preparatory attention interval which precedes the S2 (imperative) stimulus. Trial by trial LORETA analysis found similar brain rhythm generators during both pre-S1 and pre-S2 intervals. Each theta, alpha and beta traditional EEG rhythm originates in several anatomically distinct brain structures. Preparatory attention is associated with a decrease in power in alpha (right and left occipital and temporal areas) and low-beta (left frontal, bilateral occipital and middle frontal areas) EEG bands. In these structures power changes associated with preparatory attention modulated either a dominant or a non-dominant oscillatory band, suggesting that non-dominant rhythms of a cerebral area have some functional relevance. Our results imply distributed regional sources for brain rhythms and support the view that during preparatory attention there is a modulation of the brain sources generating alpha and beta brain rhythms. Moreover, the proposed combined approach makes it possible to explore the definition of a given brain area not only anatomically, but also by the frequency content and the functional reactivity of the electrical rhythms that it generates.

Alternate response preparation in a visuomotor serial task

The preparation of a particular motor pattern is related to the information available that enables the actor to predict the correct response to a forthcoming stimulus. In many situations, however, prediction is not possible. In such cases, the individual can guess the probable parameters of the next stimulus. The authors attempted to establish the bias in the motor intention for movement and its interaction with a possible memory trace of the stimulus-response mapping produced by the preceding stimulus. Two letters were presented bilaterally, and participants (N=21) had to discriminate the target letter and respond with the compatible hand. The present findings support the existence of a memory trace of the previous stimulus-response mapping.

Gender differences in event-related potentials during visual-spatial attention

The aim of present work is to test possible gender differences in the ERPs to the standards during the performance of a visual-spatial attention task. The sample: 20 subjects (10 women) aged 18-24. Electrodes: F3, F4, C3, C4, P3, P4, T5, T6, O1, O2. ANOVA tests were computed with the following factors: attention, gender, visual field, hemisphere, and electrodes. Results showed that men presented higher amplitudes in P1 and in P3b than did women, and women presented higher amplitudes in the temporal N1 than did men. For the P3, the amplitude in frontal-central regions for the attended condition was higher in men than in women, and men presented a gender-specific right frontal functional asymmetry that was not present in women. Since these components are related with the modulation of visual processing by the effect of spatial attention, the intra- and inter-gender differences obtained suggest possible differences in the processing of visual information in both genders. However, the fact that the brain generators could have a different orientation is also a possible explanation for the differences obtained in the ERPs in both genders.

Preparatory visuo-motor cortical network of the contingent negative variation estimated by current density

The present report studied the intracerebral current density of the contingent negative variation (CNV) during a visuo-manual task using the gap paradigm. The CNV is usually obtained during preparatory periods for perception and action. In this experiment right-hand responses were required. The CNV potential was obtained during the preparatory period from electrodes placed at 58 scalp sites. The CNV showed an early and a late phase. Scalp voltage and source current density maps showed that the early phase was focused on frontal midline sites. The late phase had two foci, one overlying the primary motor cortex and one over occipital sites. When analyzed by low-resolution tomography, the early phase of the CNV showed activations in the supplementary motor area (SMA), the anterior cingulate cortex (ACC), and some posterior areas. The late phase had anterior activations in the left prefrontal cortex, middle frontal cortex, primary motor cortex, ACC, and SMA; and several posterior activations including those in the medial occipital cortex, middle inferior occipital cortex, posterior cingulate cortex, and temporal and parietal areas. Results from the activated areas and their temporal dynamics during the preparatory period suggest that the ACC and the SMA areas recruit the action- and perception-related areas needed to process the expected subsequent imperative task.

Sensory and motor attentional modulation during the manual gap effect in humans: a high-density ERP study

The present study investigated reaction time (RT) and event-related potential (ERP) differences between gap and step conditions using visual stimulation and manual responses. RTs during the gap condition were facilitated with respect to those of the step condition. The ERPs, which were obtained from electrodes placed at 58 scalp sites, showed differences when the gap and step conditions were compared for the following components: an early positive component centred at the vertex, an enhanced P1 component, a frontal negativity, a negative lateralized motor potential, and an increased P3. All these results suggest that the facilitation induced by the gap is mediated by a modulation of the neural circuits involved in sensory, motor, and cognitive functions.

Temporal evolution of alpha and beta bands during visual spatial attention

Event-related potentials (ERPs) are an electrophysiological index of various cognitive processes such as attention. However, this kind of analysis does not allow observation of differences in the spectral content taking place during a sensory, cognitive or motor task. The goal of the present work was to compute the temporal dynamics of EEG oscillations using a technique called temporal spectral evolution (TSE). The electroencephalogram (EEG) was recorded during the presentation of flashed stimuli that were randomly presented to the left or right visual field. Subjects were asked to pay attention, alternately in different blocks of trials, to the left or to the right to detect an infrequent target. The results showed a decrease in the alpha band in a time window of 375-500 ms and an increase in the beta band at 500-875 ms after stimulus onset, for both attended and unattended stimuli. Statistical analysis showed that the decrease in alpha and the increase in beta were more marked during the attentional condition. In conclusion, these results demonstrate that the decrease in alpha band and the increase in beta band are electrophysiological markers of visual spatial attention.

[Temporal spectral evolution of electroencephalogram. Methodology and applications]

INTRODUCTION

The event related potentials (ERPs) allow to study the evolution of the cerebral electric activity related with the diverse sensorial, motors and cognitive processes. However, the ERPs and the spectral analyses based in Fast Fourier Transform, are not able to show the variations along the time of the spectral content of the electroencephalogram (EEG).

OBJECTIVE

The present work will show the necessary methodology to obtain the temporal dynamics of the frequency (TSE) in the EEG, a technique described by Salmelin and Hari (1994) that allows the analysis of the modulations of any spectral band along the time.

SUBJECTS AND METHODS

The presented data correspond to the electroencephalographic registration of 20 human subjects during an experiment of visual spatial attention.

RESULTS

The modulations of the ERPs differ of the observed by the spectral techniques in latency and topography. Likewise, comparing different spectral techniques is proven that the TSE allows to define with more temporal precision the variations on the spectral content.

CONCLUSION

The application of the TSE technique to the same EEG signal that is used for obtaining the ERPs, allows the inclusion of the variable time in the spectral analysis of the EEG, what can be crucial to understand the physiological bases of some neuropathologies.

Current source density analysis of CNV during temporal gap paradigm

The present report studied the contingent negative variation during Gap and Non-Gap conditions using visual stimulation and manual responses. The reaction times during the Gap condition were facilitated compared with those of the Non-Gap condition. The contingent negative variation component was obtained during the preparatory period from electrodes placed at 58 scalp sites for both Gap and Non-Gap conditions. The comparison between both conditions: Gap and non-gap did not show statistically significant differences during the preparatory period. The topography of the voltage and current source density maps showed three different foci: (i) an early negativity centred in electrodes overlying the supplementary motor area and cingulate motor areas, (ii) an activation over the primary motor cortex contralateral to the finger movement, and (iii) a bilateral activation on posterior sites. All these results suggest that the facilitation induced by the warning stimuli occurs in neural circuits that would be recruited for the subsequent processing of the imperative stimulus. The facilitation of the reaction times during the gap condition with respect to non-gap condition must be justified by neural events occurring during the gap period.

The initial orienting response during human REM sleep as revealed by the N1 component of auditory event-related potentials

The large N1 wave of the auditory event-related potentials (ERPs) typically occurring to the first stimulus after a long silent interval seems to be associated with the involuntary initial-orienting response. Since the mechanisms involved in the generation of this brain response are assumed to be activated automatically, the present study aims at determining whether this electrophysiological response can also be elicited during human REM sleep, the sleep stage considered most sensitive to external stimuli. To achieve this goal, the auditory N1 wave was analyzed in wakefulness and REM sleep for frequency deviant tones delivered in several positions (1, 2, 4 and 6) within homogenous stimulus trains separated by different intervals of silence (3, 6 and 9 s), the intra-train stimulus interval being 600 ms. A significant increment in the amplitude of the N1 component for the first deviant tone, as compared with deviants delivered in remaining positions, was observed in both brain states, independently of the inter-train interval length. This result cannot be explained by a release-from-refractoriness effect, since only one deviant was presented in each train and the inter-deviant interval hardly changed from one train to another. The increase in N1 to the first stimulus of the train, probably due to the contribution of the neuronal elements responsible for the supratemporal and non-specific components, may be explained by changes in the silent interval, rather than by variations in the stimulus frequency. The enhanced N1 could be reflecting a general increase in sensory sensitivity associated with the arousal factor of the orienting response. These findings suggest that the brain maintains the potential ability to trigger the brain events responsible for the OR elicitation, even during REM sleep.

Apolipoprotein E genotyping in a sample of Colombian patients with Alzheimer's disease

Apolipoprotein E e4 (APOEe4) allele has been associated with an increased risk for Alzheimer's disease (AD) in diverse populations. Few studies have been carried out in Hispano-Americans and results are inconclusive due to ethnic diversity. This study determined the frequency of APOE alleles in a group of 61 Caucasian-Mestizos patients with probable AD, and 61 age- and sex-matched controls. APOEe4 frequency was 36.8% for patients, and 8.2% for controls (P < 0.0001; OR 7.6). Genotype frequencies differ between the two groups (P < 0.0001). Genotype 3/3 was the most common. Frequency of genotypes 3/4, 4/4 and 2/4 were higher in patients than in the controls. Our results show a highly significant association of APOEe4 with AD, and implies the importance of APOEe4 as a risk factor in this population.

Binding of a fluorescent dansylcadaverine-substance P analogue to negatively charged phospholipid membranes

We have investigated the binding of a new dansylcadaverine derivative of substance P (DNC-SP) with negatively charged small unilamellar vesicles composed of a mixture of phosphatidylcholine (PC) and either phosphatidylglycerol (PG) or phosphatidylserine (PS) using fluorescence spectroscopic techniques. The changes in fluorescence properties were used to obtain association isotherms at variable membrane negative charges and at different ionic strengths. The experimental association isotherms were analyzed using two binding approaches: (i) the Langmuir adsorption isotherm and the partition equilibrium model, that neglect the activity coefficients; and (ii) the partition equilibrium model combined with the Gouy-Chapman formalism that considers electrostatic effects. A consistent quantitative analysis of each DNC-SP binding curve at different lipid composition was achieved by means of the Gouy-Chapman approach using a peptide effective interfacial charge (v) value of (0.95 +/- 0.02), which is lower than the physical charge of the peptide. For PC/PG membranes, the partition equilibrium constant were 7.8 x 10(3) M(-1) (9/1, mol/mol) and 6.9 x 10(3) M(-1) (7/3, mol/mol), whereas for PC/PS membranes an average value of 6.8 x 10(3) M(-1) was estimated. These partition equilibrium constants were similar to those obtained for the interaction of DNC-SP with neutral PC membranes (4.9 x 10(3) M(-1)), as theoretically expected. We demonstrate that the v parameter is a determinant factor to obtain a unique value of the binding constant independently of the surface charge density of the vesicles. Also, the potential of fluorescent dansylated SP analogue in studies involving interactions with cell membranes is discussed.

Decay time of the auditory sensory memory trace during wakefulness and REM sleep

In a repetitive auditory stimulus sequence, deviant infrequent tones typically elicit a component of auditory event-related potentials termed mismatch negativity (MMN). The elicitation of MMN is assumed to reflect the existence of a memory trace of the standard stimulus that has a decay time of about 10 s and is strengthened by repetition of the standards. The main aim of the present study was to test the decay time of the sensory memory trace during rapid-eye movement (REM) sleep vs. wakefulness, as indexed by the MMN. Subjects were presented 10 tone trains, separated by 3, 6, or 9 s of silence, during waking and REM sleep. Each train consisted of 9 standards of 1000 Hz and 1 deviant of 2000 Hz that occurred at position 1, 2, 4, or 6. The waking deviants elicited a frontocentral negativity with a scalp topography equivalent to the MMN component. During REM sleep, the negative component showed the same scalp distribution only for the 3-s intertrain interval (ITI). In this brain state, the MMN amplitude was smaller and decreased with prolongation of the ITI. These results suggest a weaker sensory memory trace formation and a premature decay time of such a memory trace during REM sleep as compared with wakefulness.

Alpha EEG coherence in different brain states: an electrophysiological index of the arousal level in human subjects

The functional relationships between the brain areas supposedly involved in the generation of the alpha activity were quantified by means of INTRA- and INTER-hemispheric coherences during different arousal states (relaxed wakefulness, drowsiness at sleep onset, and rapid eye movement sleep) where such an activity can be clearly detectable in the human EEG. A significant decrease in the fronto-occipital as well as in the inter-frontal coherence values in the alpha range was observed with the falling of the vigilance level, which suggests that the brain mechanisms underlying these coherences are state dependent. Making fronto-frontal coherence values in the alpha frequency band useful indexes to discern between brain functional states characterized by a different arousal level.

Brain spatial microstates of human spontaneous alpha activity in relaxed wakefulness, drowsiness period, and REM sleep

Spontaneous alpha activity clearly present in relaxed wakefulness with closed eyes, drowsiness period at sleep onset, and REM sleep was studied with spatial segmentation methods in order to determine if the brain activation state would be modulating the alpha spatial microstates composition and duration. These methods of spatial segmentation show some advantages: i) they extract topographic descriptors independent of the chosen reference (reference-free methods), and ii) they achieve spatial data reduction that are more data-driven than dipole source analysis. The results obtained with this study revealed that alpha activity presented a different spatio-temporal pattern of brain electric fields in each arousal state used in this study. These differences were reflected in a) the mean duration of alpha microstates (longer in relaxed wakefulness than in drowsy period and REM sleep), b) the number of brain microstates contained in one second (drowsiness showed more different microstates than did relaxed wakefulness and REM state), and c) the number of different classes (more abundant in drowsiness than in the rest of brain states). If we assume that longer segments of stable brain activity imply a lesser amount of different information to process (as reflected by a higher stability of the brain generator), whereas shorter segments imply a higher number of brain microstates caused by more different steps of information processing, it is possible that the alpha activity appearing in the sleep onset period could be indexing the hypnagogic imagery self-generated by the sleeping brain, and a phasic event in the case of REM sleep. Probably, REM-alpha bursts are associated with a brain microstate change (such as sleep spindles), as demonstrated by its phasic intrusion in a desynchronized background of brain activity. On the other hand, alpha rhythm could be the "baseline" of brain activity when the sensory inputs are minimum and the state is relaxed wakefulness.

Altered pharmacokinetics of ceftazidime in critically ill patients

Many critically ill patients have increased extracellular fluid which might affect ceftazidime pharmacokinetics. We investigated the pharmacokinetics of ceftazidime in 15 adult intensive care patients receiving 2 g of ceftazidime intravenously three times a day. The ceftazidime mean (standard deviation) apparent volume of distribution and terminal-phase half-life were 56.91 (25.93) liters and 4.75 (1.85) h, respectively, significantly greater than values reported previously for healthy controls (P < 0.001). The mean ceftazidime clearance and area under the curve at steady state were not significantly different from those previously reported for controls. We conclude that ceftazidime pharmacokinetics in critically ill patients were altered by an increased volume of drug distribution and elevated elimination half-life.

Frequency analysis of the EEG during spatial selective attention

In this study, we recorded the event-related potentials (ERPs) elicited by stimuli appearing at attended and unattended locations. The voltage amplitudes and latencies of the P1, N1, P2, N2 and P3 visual components showed statistically significant differences in the attended condition with respect to the unattended one. The power spectral density of the EEG following stimulus onset was calculated. The difference between the spectral densities of the attended and unattended conditions was computed. Statistically significant differences were found in the decrease of alpha (9-11 Hz) and the increase of beta (15-17 Hz) frequencies during the attention condition with respect to the unattended condition. These results suggest that the arrival of a visual stimulus during the attended condition generates a complex reorganization of neuronal activity in both time and frequency domains.

The mismatch negativity component reveals the sensory memory during REM sleep in humans

Auditory evoked potentials (AEPs) were recorded during presentation of stimuli of 1000 Hz (standard) and 2000 Hz (deviant) in trains of 10 tone bursts (one deviant per train) in the wake and rapid eye movement (REM) sleep states. The constant inter-stimulus interval (ISI) was 600 ms and the trains were separated by 3 s of silence. The deviant tone occurring at the train start elicited a mismatch negativity component (MMN) in both arousal states, displaying a peak latency between 100 and 150 ms post-stimulation at fronto-central areas. These results suggest the existence of an auditory memory trace (sensory memory) surviving for at least 3 s during REM sleep.

A fluorescence spectroscopy study of the interaction of monocationic quinine with phospholipid vesicles. Effect of the ionic strength and lipid composition

The interaction of monocationic quinine with zwitterionic dimyristoyl phosphatidylcholine (DMPC) and mixed negatively-charged dimyristoylphosphatidyl glycerol (DMPG)/DMPC small unilamellar vesicles in the liquid-crystalline phase was investigated by steady-state fluorescence spectroscopy at pH 7 and 37 degrees C. The maximum fluorescence emission peak at 383 nm, upon excitation at 335 nm, shifts to lower wavelength and decreases its intensity as the ratio between the total lipid and quinine concentrations increases. This indicates that in the membrane-bound state quinine is in an environment of low polarity, more deeply buried when anionic DMPG is present in the vesicle. For monoprotonated quinine/DMPC system the corresponding association isotherms show that the extension of binding is slightly enhanced as the ionic strength decreases, whereas for mixed DMPG/DMPC vesicles at low ionic strength, the association of the drug is favoured as the percentage of anionic DMPG increases. The binding curves have been quantitatively analyzed by the binding and the partition models including in this latter an activity coefficient, gamma, to account for non ideal quinine interactions. It is demonstrated for both neutral and anionic membranes that the activity coefficient approaches the unity and that the deviation from ideality is mainly due to electrostatic forces.

Binding of basic amphipathic peptides to neutral phospholipid membranes: a thermodynamic study applied to dansyl-labeled melittin and substance P analogues

A thermodynamic approach is proposed to quantitatively analyze the binding isotherms of peptides to model membranes as a function of one adjustable parameter, the actual peptide charge in solution z(p)+. The main features of this approach are a theoretical expression for the partition coefficient calculated from the molar free energies of the peptide in the aqueous and lipid phases, an equation proposed by S. Stankowski [(1991) Biophysical Journal, Vol. 60, p. 341] to evaluate the activity coefficient of the peptide in the lipid phase, and the Debye-Hückel equation that quantifies the activity coefficient of the peptide in the aqueous phase. To assess the validity of this approach we have studied, by means of steady-state fluorescence spectroscopy, the interaction of basic amphipathic peptides such as melittin and its dansylcadaverine analogue (DNC-melittin), as well as a new fluorescent analogue of substance P, SP (DNC-SP) with neutral phospholipid membranes. A consistent quantitative analysis of each binding curve was achieved. The z(p)+ values obtained were always found to be lower than the physical charge of the peptide. These z(p)+ values can be rationalized by considering that the peptide charged groups are strongly associated with counterions in buffer solution at a given ionic strength. The partition coefficients theoretically derived using the z(p)+ values were in agreement with those deduced from the Gouy-Chapman formalism. Ultimately, from the z(p)+ values the molar free energies for the free and lipid-bound states of the peptides have been calculated.

Deglycosylation of asparagine-linked glycans by peptide:N-glycosidase F

Endo-beta-N-acetylglucosaminidase F (Endo F) and peptide:N-glycosidase F (PNGase F) were purified from cultures of Flavobacterium meningosepticum by ammonium sulfate precipitation followed by gel filtration on TSK HW-55(S). This system separated the two enzymes and provided PNGase F in a high state of purity, but the basis for the resolution appeared to be hydrophobic interaction and not molecular size. Studies using purified Endo F and PNGase F with defined glycopeptides demonstrated that Endo F was somewhat similar to Endo H in that it hydrolyzed many, but not all, high-mannose and hybrid oligosaccharides, as well as complex biantennary oligosaccharides. PNGase F, in contrast, hydrolyzed all classes of asparagine-linked glycans examined, provided both the alpha-amino and carboxyl groups of the asparagine residue were in peptide linkage. Deglycosylation studies with PNGase F revealed that many proteins in their native conformation were susceptible to this enzyme but that prior denaturation in sodium dodecyl sulfate greatly decreased the amount of enzyme required for complete carbohydrate removal.