Matching Pursuit (MP) a method of high-resolution signal analysis is described in the context of other methods operating in time-frequency space. The method relies on an adaptive approximation of a signal by means of waveforms chosen from a very large and redundant dictionary of functions. The MP performance is illustrated by simulations and examples of sleep spindles and slow wave activity analysis. An improvement of the original procedure, relying on the introduction of stochastic dictionaries, is proposed. A comparison of the performance of dyadic and stochastic dictionaries is presented. MP with stochastic dictionaries is characterized by an unmatched resolution in time-frequency space; moreover it allows for parametric description of all (periodic and transient) signal features in the framework of the same formalism. Matching pursuit is especially suitable for analysis of non-stationary signals and is a unique tool for the investigation of dynamic changes of brain activity.
We describe nonlinear deterministic versus stochastic methodology, their applications to EEG research and the neurophysiological background underlying both approaches. Nonlinear methods are based on the concept of attractors in phase space. This concept on the one hand incorporates the idea of an autonomous (stationary) system, on the other hand implicates the investigation of a long time evolution. It is an unresolved problem in nonlinear EEG research that nonlinear methods per se give no feedback about the stationarity aspect. Hence, we introduce a combined strategy utilizing both stochastic and nonlinear deterministic methods. We propose, in a first step to segment the EEG time series into piecewise quasi-stationary epochs by means of nonparametric change point analysis. Subsequently, nonlinear measures can be estimated with higher confidence for the segmented epochs fullfilling the stationarity condition.
Bilateral, electrolytic lesion of the lateral hypothalamus (LH) in rats produces hyposomnia and qualitative EEG changes which are difficult to assess by convencional visual inspections of electroencephalograms. In the present study the spectral analysis of EEG was applied in LH-lesioned rats and confronted with standart visual scoring method. One-hour samples of hippocampal and cortical EEG were taken from the light part of the circadian cycle before and after electrolytic or sham LH damage. In half of the LH-lesioned rats a power spectral analysis was performed using a Fast Fourier Transform routine at 1 Hz bands from 0.5 to 25 Hz; in the other half, as well as in the sham-lesioned group, EEG records were visually scored for the amount of waking, slow wave sleep and paradoxical sleep. Significant hyposomnia effects were found in LH-lesioned rats. Power spectral analysis of hippocampal EEG revealed a significant increase in power density at 4-6 Hz and reduction at 7-10, 14-17, 19-22 and 23-24 Hz. In neocortical EEG there was a significant increase in power density at 5-6 Hz band and reduction at 7-8 Hz. The results are discussed in the context of the effects of selective desrtuction of the specific neurotransmitter systems occupying the LH area.
Since electroencephalographic (EEG) signal may be considered chaotic, Nonlinear Dynamics and Deterministic Chaos Theory may supply effective quantitative descriptors of EEG dynamics and of underlying chaos in the brain. We have used Karhunen-Loeve decomposition of the covariance matrix of the EEG signal to analyse EEG signals of 4 healthy subjects, under drug-free condition and under the influence of Diazepam. We found that what we call KL-complexity of the signal differs profoundly for the signals registered in different EEG channels, from about 5-8 for signals in frontal channels up to 40 and more in occipital ones. But no consistency in the influence of Diazepam administration on KL-complexity is observed. We also estimated the embedding dimension of the EEG signals of the same subjects, which turned to be between 7 and 11, so endorsing the presumption about existence of low-dimensional chaotic attractor. We are sure that nonlinear time series analysis can be used to investigate the dynamics underlying the generation of EEG signal. This approach does not seem practical yet, but deserves further study.
The present work presents three experiments investigating cortical activities in the gamma band in humans. On the basis of theoretical models and animal experiments, synchronized oscillatory neuronal activity is discussed as the key mechanism by which the brain binds information processesed in different cortical areas to form a percept. Using an identical stimulation design - the same as used in animal studies - it was shown that induced gamma band responses in the EEG resemble the same features as those found in the intracortical recordings of animals. In addition, the present work demonstrates that these cortical activities are not higher harmonics of the alpha band and that they are senstive to the features of the stimulus. These results support the notion that gamma band activity is not just a by-product of neuronal activity and that alpha- and gamma band activies most certainly represent different cortical funtional states.
The pedunculopontine tegmental nucleus (PPN) is one of the reticular generators of the hippocampal theta rhythm. The PPN neuronal circuitry related to theta generation involves its cholinergic, GABA-ergic and glutamatergic components. Here we provide data indicating that the PPN tachykinin system may also be a part of this circuitry. In the experimental model of the tail-pinch elicited hippocampal theta in urethane-anesthetized rats (implanted with bilateral recording electrodes in the stratum moleculare of the upper blade of the dentate gyrus and with injection cannula unilaterally inserted into the PPN) it was found that intra-PPN microinjection of Substance P (SP) and [d-Pro2, d-Phe7, d-Trp9]-Substance P (DPDPDT) caused suppression of the theta and enhancement of the delta activity in the hippocampal EEG. Accordingly, there was approximately a 50% (SP) -70% (DPDPDT) decline of the peak power in the theta frequency range and a decrease by 0.4 Hz in the corresponding peak frequency (DPDPDT only) in both hippocampi. The circuitry through which SP exerts its effect in the PPN can be only hypothetical at present. We suggest SP-evoked activation (either direct or indirect through the glutamatergic inputs) of the GABA interneurons which may tonically inhibit PPN outputs to the other theta-relevant structures.
Spontaneous EEG of 21 healthy human subjects obtained by standard procedure of recording is analysed using non-linear prediction methods to check whether the signals were generated by a non-linear dynamics process or by a linear stochastic process. The test for non-linearity is performed by surrogate data method with non-linear prediction error as the test statistic. The null hypothesis that EEG signal (in rest, with eyes closed) is generated by linear stochastic process can be rejected in 17 cases (5%) out of the 336 (21 subjects, 16 channels) studied epochs. However, most of these rejections concern 3 subjects. The 88% of rejections of the null hypothesis concern frontal channels. The null hypothesis is not rejected for epochs recorded with eyes open and during photostimulation.
This paper presents a hybrid method for localization of oscillatory EEG activity. It consists of two steps: multichannel matching pursuit with complex Gabor dictionary, and LORETA inverse solution. Proposed algorithm was successfully applied to the localization of epileptogenic EEG in a single patient.
The study investigates the possibility of combined recording event-related potentials (ERPs) and functional MRI (fMRI). Visual evoked potentials (VEPs) were elicited by an alternating black and white checkerboard, which was presented blockwise outside the static 1.5 T magnetic field and during an echo planar imaging (EPI). An fMRI sequence with a time window for interleaved EEG-measurement and a measurement protocol which reduces pulse artifacts and vibrations was used. Thus, during an EPI sequence, it was possible to detect VEPs which had the same structure and latencies as VEPs outside the magnetic field and which corresponded well with the observed activated areas of the visual cortex.
Co-variation between subjectively estimated mood/activation and EEG characteristics, based on spectral power parameters, was investigated. Subjective estimation of mood was made by using Thayer's Activation-Deactivation Adjective Checklist, which yielded two dimensions: Energy-Tiredness (with Energy pole having positive valence connotation) and Tension-Calmness (negative connotation for Tension). A within-subject design with two sessions of EEG recording immediately followed by mood assessment was applied. These were separated by a cognitive task, introduced in order to modify the subjects' mood. The correlations between changes in mood estimation and changes in EEG spectral power parameters were calculated. Both ADACL dimensions co-varied with EEG in a specific way according to frequency and localization. Subjective estimation of Energy correlated negatively with alpha1 and, surprisingly, positively with delta, theta1 as well as theta2 relative power. Estimation of Tension correlated positively with theta1 and beta1, and negatively with alpha2 relative power. Presented results suggest that the adjective description of mood has objectively-measurable brain correlates in the EEG.
Oscillations are a prominent feature of macroscopic human sensorimotor cortical activity as recorded non-invasively with electroencephalography (EEG) and magnetoencephalography (MEG). The advent of whole-scalp MEG systems allowing rapid non-invasive recording from the entire cortex and accurate localisation of neural sources, and the development of refined signal analysis methods are important factors that led to an increasing interest in studies of sensorimotor oscillations during the last 10 years. Investigations on healthy subjects revealed frequency-specific localisation and modality-specific reactivity of 10 Hz and 20 Hz sensorimotor oscillations. Task-specific coherence between motor cortical and electromyographic oscillations, reflecting cortico-motoneuronal coupling, point towards a functional role of precentral oscillations in the cortical control of voluntary movements. Furthermore, abnormal cortico-motoneuronal coupling may underlie clinical symptoms of motor disorders, such as tremor. Thus, investigation of oscillatory sensorimotor activity proceeds from phenomenology to function and provides an interesting approach to address questions in human motor physiology and pathophysiology.
The Short-Time Directed Transfer Function (SDTF) is an estimator based on a multivariate autoregressive model which has proved to be successful in ERP experiments, e.g. those connected with motor action and its imagination. The aim of this study is the evaluation of the performance of SDTF in the cognitive experiment. We have applied SDTF for the estimation of the pattern of EEG signal transmissions during a Continuous Attention Test (CAT). Time-frequency patterns of propagation were estimated for two experimental conditions. Statistical procedures based on thin-plate spline model were used for estimation of significant changes in respect to the reference epoch. The repeatability of the results for a subject and across the subjects were investigated. The effect of prolonged transmission in the gamma band from the prefrontal electrodes found in all subjects was explained by the active inhibition in the case when a subject had to sustain from performing the action.
The question of nonlinearity in the human electroencephalogram (EEG) is important, since linear methods of EEG analysis are more well-developed and computationally faster than nonlinear methods. Furthermore, the presence or absence of nonlinearity has important theoretical implications for understanding the nature of the brain's oscillatory activity. Using a linear summary measure as a control, we report a failure to reject the null hypothesis of a (largely) stationary linear-Gaussian process for normal, resting, eyes-closed EEG from a single participant. We found significant evidence of nonlinearity at two occipital sites (O1 and O2) where the 8-12.5<%0> Hz alpha rhythm was prominent. However, this element of nonlinear structure appeared trivial, as (1) we found no evidence of time irreversibility at these loci, and (2) best-fitting linear models accounted on-average for over 94% of the variance in the data with nonlinear modeling doing no better. Half of the remaining variance could be accounted for by nonstationarity. While our findings technically apply only to the one individual tested, his EEG was typical of those seen under the conditions that we employed.
Autistic spectrum disorders (ADS) and epilepsy are common pediatric neurological disorders. Prevalence of both is estimatedat approximately 1% in the population. These two disorderscan appear separately or coexist in the same person, often with concomitant specific developmental disorders and intellectual disability.The comorbidity of ASD and epilepsy is well known and the occurrence of epilepsy in ASD ranges, according to various authors, from 2,7%–46%.The relationship between ASD and epilepsy is bidirectional: patients firstly diagnosed with ASD can develop epilepsy, andconversely, children with epileptic seizures can develop autistic symptoms. The recent studies indicate that epilepsy occurrsmore frequently in patients with ASD [13,7%] than ASD amongpatients with epilepsy [3,4%]. The crucial risk factor in both casesis intellectual disability.The risk of developing epilepsy in patients with ASD according to the literature data ranges from 6–46%. ASD studies indicated that there is no dominant type or epilepsy syndrome. However, most scientists indicate that partial seizures are the most commonly reported. The risk of developing epilepsy is greater in the older children and in patients with lower IQ. On the other hand, children firstly diagnosed with epilepsy can also develop ASD; according to published data the risk is from3,4%–37%, the highest among children with the early onset and with frequent seizures. The higher risk of ASD is also related to other various epileptic syndromes (infantile spasms, Dravet syndrom) and in children with developmental disorders and intellectual disability.In many works, common pathophysiological mechanisms have been shown to underlie both of these diseases Appearance of both could be determined by structural abnormalities in CNS, genetic and environmental factors, metabolic disorders or perinatal injuries.
PL
Zaburzenia ze spektrum autyzmu (ASD) i padaczka należą do częstych zaburzeń neurologicznych u dzieci. Częstość ich występowania szacuje się na około 1% populacji. Schorzenia te mogą występować niezależnie lub współwystępować u tej samej osoby, często z towarzyszącymi specyficznymi zaburzeniami neurorozwojowymi oraz niepełnosprawnością intelektualną. Współwystępowanie ASD i padaczki jest dobrze znane w literaturze, a występowanie padaczki w ASD szacuje się, wg różnych autorów od 2,7% do 46%. Związek między ASD i padaczką jest dwukierunkowy: u pacjentów z rozpoznaniem ASD może rozwinąć się padaczka i odwrotnie u pacjentów z napadami padaczkowymi mogą pojawić się cechy autyzmu. Podkreśla się jednak częstsze występowanie padaczki u pacjentów z ASD (13,7%) niż ASD u pacjentów z padaczką (3,4%). Istotnym czynnikiem ryzyka w obu przypadkach jest niepełnosprawność intelektualna. Ryzyko rozwoju padaczki u pacjentów z ASD wynosi wg różnych autorów od 6% do 46%. W ASD nie odnotowano dominującego typu lub zespołu padaczkowego. Jednak większość badaczy wskazuje na najczęstsze występowanie napadów ogniskowych. Ryzyko rozwoju padaczki jest większe u dzieci starszych oraz u pacjentów z niskim ilorazem inteligencji. Z drugiej strony u dzieci z rozpoznaną padaczką może również rozwinąć się ASD, wg danych z piśmiennictwa ryzyko wynosi od 3,4% do 37%, najwyższe u dzieci z wczesnym początkiem i dużą częstością napadów. Większe ryzyko rozwoju ASD istnieje również w różnych zespołach padaczkowych (zespół Westa, zespół Dravet) a także u dzieci z opóźnieniem rozwoju i niepełnosprawnością intelektualną. W wielu pracach wykazano wspólne mechanizmy patofizjologiczne obu tych schorzeń. Obecność padaczki i ASD może być zdeterminowana zmianami strukturalnymi OUN, czynnikami genetycznymi oraz zaburzeniami metabolicznymi, środowiskowymi i okołoporodowymi, które odgrywają istotną rolę w patogenezie zarówno padaczki jak i autyzmu.
The aim of the present paper is the assessment of the overall complexity of spontaneous and non-paroxysmal EEG signals obtained from three groups of human subjects, e.g., healthy, seizure and mania. Linear complexity measure suitable for multi-variate signals, along with nonlinear measures such as approximate entropy (ApEn) and Taken?s estimator are considered. The degree of linear complexity is significantly reduced for the pathological groups compared with healthy group. The nonlinear measures of complexity are significantly decreased in the seizure group for most of the electrodes, whereas a distinct discrimination between the maniac and healthy groups based on these nonlinear measures is not evident.
As the world moves towards the Fourth Industrial Revolution, there is a need for formulations of neurophysiological biomarkers that ensure the accuracy of the diagnosis of visual perception dysfunction in individuals with Autism Spectrum Disorder (ASD). Biomarkers of visual perception dysfunction in ASD using EEG complements behavioral methods of diagnosis and allows for a more direct assessment of the dysfunction, identifying rapid, implicit neural processes that are not revealed through behavioral measures alone. This paper aims to review the neural biomarkers of the five domains of visual perception dysfunction (visual discrimination (VD), visual spatial relations (VSR), visual form constancy (VFC), visual memory (VM) and visual closure (VC)) in individuals with ASD. This paper shall help researchers gain new insight into the current trends and progress in EEG methods in ASD and discover gaps in the subject literature. A systematic literature search on PubMed was conducted to report findings of EEG studies that:1) assessed the severity levels in patients with ASD and 2) investigated the neural biomarkers of visual perception dysfunction in ASD. Spectral analysis, functional connectivity analysis and event-related potential (ERP) are useful in modern medicine to identify the biomarkers that distinguish the levels of the severity of visual perception dysfunction in ASD.
Earlier in vivo studies conducted on freely moving and anesthetized rats demonstrated that the posterior hypothalamus (PH) comprises pathways critical for producing the synchronous hippocampal formation (HPC) theta rhythm. In addition, these findings suggested that the frequency of the HPC theta was encoded in the PH and then was fed via the medial forebrain bundle to the medial septum and HPC. In the present study we attempted to verify this hypothesis with use of a different in vivo model - freely moving cats. The microinjection of the local anaesthetic, procaine, into the PH region reversibly suppressed the spontaneous as well as sensory and electrically induced HPC theta. However, in contrast to rats, in freely moving cats microinjection of procaine into the PH reduced the amplitude of the HPC theta but had no effect on theta frequency. We conclude that in freely moving cats the PH region comprises a critical part of the ascending brainstem pathway, for production of the HPC theta rhythm. In contrast to rats, in freely moving cats ascending inputs from the brainstem to the PH contribute mainly to the amplitude of the HPC theta rhythm.
It was found previously that unilateral destruction of the ventral tegmental area (VTA) facilitated behavioral responses (exploration, eating) induced by electrical stimulation of the contralateral VTA. The same effect occurred after unilateral injections of pharmacological agents, which led to a decrease in dopaminergic transmission in the VTA. While trying to explain the mechanism behind this 'contralateral facilitation effect' in the present experiment we examined whether augmentation of function of the contralateral hemisphere would be reflected in cortical and hippocampal EEG changes in conscious rats. Unilateral, cytotoxic lesion of the VTA caused a bilateral decrease in neocortical and hippocampal EEG power during both exploratory sniffing and eating. Depression involved all the frequency bands in the prefrontal cortex, mainly in the hemisphere contralateral to the VTA lesion. In the hippocampus the depression was slightly more intense ipsilaterally, also involving all the frequency bands although to different degrees. The results indicate that the VTA is involved in the regulation of cortical and hippocampal activity during VTA-dependent behavioral activation, and that the 'contralateral facilitation effect' is concomitant with lateralized changes in EEG activity.
The aim of this study was to examine the neurophysiological correlates of cognitive dysfunctions in a patient with the minimally verbal variant of Autism Spectrum Disorder (ASD + MV), who after reaching adulthood showed progressive deterioration of his cognitive skills. The patient was a 25-year-old male, diagnosed with ASD. He never developed spoken language, and communicated only by gesturing or writing on a computer. Our findings confirmed comorbidity of ASD and epilepsy, accompanied by dysfunction of cognitive control. We also found that spontaneous EEG and event-related potentials (ERPs) in a cued GO/NOGO task can be used to assess functional brain changes concomitant with ASD.
Light exposure at night increases alertness; however, it is not clear if light affects nocturnal alertness in the same way that it affects measures of circadian regulation. The purpose of this study was to determine if a previously established functional relationship between light and nocturnal melatonin suppression was the same as that relating light exposure and nocturnal alertness. Four levels of narrow-band blue light at the cornea were presented during nighttime sessions. The ratio of electroencephalographic alpha power density with eyes closed to eyes open (alpha attenuation coefficient, AAC) and the Norris mood scale were used. The AAC and ratings of alertness increased monotonically with irradiance and were highly correlated. Both measures of alertness were highly correlated with model predictions of nocturnal melatonin suppression for the same circadian light stimulus, consistent with the inference that the suprachiasmatic nuclei play an important role in nocturnal alertness as well as circadian regulation.
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