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1

Comparison of original and modified Canolty method for assessment of phase to amplitude cross-frequency coupling

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Bernatowicz G., Zygierewicz J.
Acta Neurobiologiae Experimentalis
|
2017
|
tom 77
|
nr Suppl.1
INTRODUCTION: Recent studies indicate that coupling between low- and high-frequency brain rhythms provides valuable information on cognitive processing in humans. One of the approaches to study these couplings is based on analysis of time-frequency representations of the ECoG or EEG signals aligned to a given phase in the low-frequency band. The method proposed by Canolty (2006) is based on time‑frequency representations obtained by bandpass filtering of the signal. Each band is normalized by means of the z-transform. AIM(S): We propose a development of Canolty’s method. The purpose of this study was to test the properties and efficacy of the enhanced method, and to compare the results to those obtained with the original Canolty’s method. METHOD(S): The proposed method relies on time--frequency representation of signal’s energy density derived from continuous wavelet transform, and normalization of each frequency relative to its average value in the baseline period (analogously to Event Related Synchronization/Desynchronization analysis). Moreover, we proposed the use of cluster‑based statistic to identify statistically significant effects. Both methods were tested on simulated signal. The simulations consist of a low-frequency sine (in the range of theta rhythm frequencies) with superimposed spindles of high-frequency (from the gamma band range) and white noise. For each method we determined the signal-to-noise ratio range where methods give reliable results, for selected ratios of gamma to theta amplitude. RESULTS: The proposed method turned out to be more sensitive and more specific. It identifies coupling only in the correct theta frequency, whereas original method localizes coupling also in neighboring frequency bands. The modified method is also more robust to higher noise levels. CONCLUSIONS: The findings suggest that the enhanced method have sufficient sensitivity to measure the theta-gamma coupling as measured by high quality EEG or ECoG.
2

Time-frequency analysis of auditory working memory

100%
Duda-Golawska J., Zygierewicz J.
Acta Neurobiologiae Experimentalis
|
2018
|
tom 78
|
nr Suppl.1
Working memory (WM) is defined as a cognitive system with a limited capacity that is responsible for temporarily holding task-relevant information (Sreenivasan et al., 2014). It is hypothesized that WM recruits the same brain areas that process sensory information. Huang et al. (2016) found, in a carefully crafted experiment that enabled the separation of ac‑ tivity related to working memory engaged in remem‑ bering tones from activity related to other mental pro‑ cesses, that there is an enhanced sustained field type activity during a high load task in sources seeded in the auditory cortex. The aim of the current study was to further analyse MEG data obtained from these au‑ ditory WM experiments for possible correlates of high WM load for tones. Specifically, we were interested in markers of auditory WM in the time-frequency do‑ main on the level of individual MEG sensors, especially those with a strong signal from the auditory cortex. We analysed 2 sec long epochs of signal from the delay period between two sounds under two different WM load conditions. We analysed contrast time-frequency maps with cluster-based extreme value statistics. The methodology and results are presented. References: Sreenivasan KK, Curtis CE, DʼEsposito M. Revisiting the role of persistent neural activity during working memory. Trends in Cognitive Sciences. 2014; 18: 82–89. Huang Y, Matysiak A, Heil P, König R, Brosch M. Per‑ sistent neural activity in auditory cortex is related to auditory working memory in humans and nonhuman primates. King AJ, ed. eLife. 2016; 5: e15441.
3

Properties and efficacy of a novel method for assessing phase to amplitude cross-frequency coupling

100%
Bernatowicz G., Zygierewicz J.
Acta Neurobiologiae Experimentalis
|
2018
|
tom 78
|
nr Suppl.1
Recent studies indicate that coupling between low‑ and high‑frequency (e.g. theta and gamma) brain rhythms provides valuable information on cognitive processing in humans. The purpose of this study was to examine the properties and efficacy of a novel method of assessment of phase to amplitude cross‑frequency coupling. The proposed method is based on analysis of time‑frequency representation of signals aligned to a given phase in the low‑frequency band. Low frequen‑ cy wave is obtained with Matching Pursuit algorithm by selecting waveforms of interest. The time‑frequency representation of a signal’s energy density is derived from the continuous wavelet transform, and normal‑ ized at each frequency relative to its average value in the baseline period. Next, the representation is thresh‑ olded at values obtained from surrogate data. The re‑ sulting maps are used to compute comodulograms. The effects presented in the comodulograms are vali‑ dated with extreme values statistics. The method was tested on synthetic signals. The first signal represents proper phase to amplitude cross‑frequency coupling. It consists of a low‑frequency sine (in the range of theta rhythm frequencies) with superimposed spin‑ dles of high‑frequency (from the gamma band range) and white noise. The second and third signals display epiphenomenal cross‑frequency coupling, which orig‑ inates from their time course. We found that the pro‑ posed method is robust for high noise levels, which suggests that it has sufficient sensitivity to detect the theta‑gamma coupling as measured by high quality EEG or ECoG. Nonetheless, it is not immune to epiphenom‑ enal cross‑frequency coupling, which warns us against drawing conclusions from positive output.
4

A comparison of methods for analysis of temporal frequency tuning in visual responses

81%
Wierzbicka A., Kordecka K., Zygierewicz J., Waleszczyk W. J.
Acta Neurobiologiae Experimentalis
|
2017
|
tom 77
|
nr Suppl.1
INTRODUCTION: There are numerous methods to study neuronal processing of information about temporal frequency content of visual stimuli. The two most fundamental methods are 1) direct measurement of response amplitude, e.g. an amplitude of averaged visual evoked potential, and 2) assessment of response magnitude after transformation of electrophysiological signal from time to frequency domain. AIM(S): The aim of this study was to find an appropriate analysis method to characterize cortical responses to visual stimuli of various temporal frequencies. METHOD(S): Visual responses were recorded from both primary visual cortices, contra- and ipsilateral to the stimulated eye, using multichannel linear electrode arrays during electrophysiology experiments performed on anesthetized rats. As a visual stimulus we used 2-ms-long LED flashes delivered at two frequencies: 1 and 7 Hz. RESULTS: We found that for frequency of 1 Hz it is difficult to draw conclusions based on power spectrum alone. For frequency of 7 Hz the assessment of evoked potential in time domain was highly inaccurate. CONCLUSIONS: For 1 Hz the estimation of the visual evoked potential amplitude by direct measurement should be also performed. For 7 Hz the analysis should be performed after transformation of the signal from the time to frequency domain. Our results also indicate the advantages of the Welch method in comparison to the periodogram to analyze signals in the frequency domain. FINANCIAL SUPPORT: Supported by the Polish National Science Center grant Symfonia 1 (2013/08/W/NZ4/00691).
5

Phase-amplitude cross-frequency coupling in rats olfactory bulb after injection of ketamine

81%
Jurkiewicz G., Hunt M. J., Zygierewicz J.
Acta Neurobiologiae Experimentalis
|
2019
|
tom 79
|
nr Suppl.1
INTRODUCTION: The injection of ketamine is an animal model of schizophrenia. It leads to behavioral changes such as hyperlocomotion and accelerated breath and electrophysiological changes such as the appearance of high‑frequency oscillations (HFO). Previous studies reported that the amplitude of HFO in the striatum is coupled with a phase of respiratory rhythm. However, recent studies suggest that the olfactory bulb is an important generator of HFO which can impose this activity in ventral striatal areas. AIM(S): The purpose of this study was to examine the LFP recording from olfactory bulb after injection of ketamine with a novel method of phase-amplitude coupling detection. METHOD(S): The proposed novel method of PAC detection is based on analysis of time‑frequency representation of signals aligned to a given phase in the low‑frequency band. Low‑frequency wave is obtained with the Matching Pursuit algorithm by selecting waveforms of interest. The time‑frequency representation of the signal’s energy density is derived from continuous wavelet transform and normalized at each frequency relative to its average value in the baseline period. Next, the representation is thresholded at values obtained from surrogate data. The resulting maps are used to compute comodulograms. The effects presented in the comodulograms are validated with extreme values statistics. RESULTS: We found statistically significant coupling between the amplitude of high‑frequency oscillation (around 150 Hz) and phase of low‑frequency oscillation (around 7 Hz) in most of the examined rats. The temporal pattern of PAC shows dependence on injection of ketamine. CONCLUSIONS: The HFO in olfactory bulb display the property of phase-amplitude coupling with low-frequency oscillation. The additional conclusion is that the proposed novel method is adequate to detect coupling in real LFP data.
6

Exploratory and classical ANOVA analysis of response-locked event-related potentials

81%
Duda-Golawska J., Imbir K. K., Zygierewicz J.
Acta Neurobiologiae Experimentalis
|
2019
|
tom 79
|
nr Suppl.1
INTRODUCTION: In the classical approach, we assume that when designing the experiment in the way described in the literature, we can observe specific components of the event‑related potential (ERP) induced in specific areas of the brain with specific latencies. Using these standard methods of data analysis, i.e., looking for activity changes only in components commonly known from the literature, there is a risk of not noticing new, interesting effects. METHOD(S): In order to check if the data-driven approach gives the opportunity to verify the classical approach and whether it allows to better match the analysis, we compared it with the classical analysis, using data from emotional experiments. We investigated the electrophysiological correlates of execution of an ambiguous task under the influence of emotionality of words stored in working memory. RESULTS: The analysis of variance (ANOVA) classical analysis of ERP was compared with an exploratory approach using GFP (Global Field Power), calculated as spatial standard deviation. Analysis of the GFP curve was used to determine the time periods in which we performed a 4‑factor ANOVA with repeated measures. CONCLUSIONS: In the present case, we were able to find significant effects related to the valence and origin consistent with classical analysis while maintaining control of the statistical significance. Phenomena were shifted in the time domain and with a tilted pattern in the spatial distribution.
7

Global field power: Time-frequency domain approach

81%
Duda J., Imbir K., Zygierewicz J.
Acta Neurobiologiae Experimentalis
|
2017
|
tom 77
|
nr Suppl.1
INTRODUCTION: Classic approach of Global Field Power (GFP) is defined as a function of time, where the GFP maxima are used to determine the latencies of evoked potential components. The GFP corresponds to the spatial standard deviation, and it quantifies the amount of activity at each time point in the field (which consider signal from all electrodes simultaneously). Its results in a reference-independent descriptor of the potential field. This study shows an extension of this method to time-frequency domain. AIM(S): The main aim of this study was to determine time windows for chosen frequency bands suitable for further statistical analysis. The criterion for selection of the time windows should rely on stability of topography of band power. METHOD(S): The frequency enabled GFP relies on estimation of instantaneous band-power and evaluation of its spatial standard deviation. Estimator of band power was obtained by band-pass filtering, followed by rectification of the signal and smoothing of the output. Analogously to the classical GFP, high value of obtained measure indicates spatial variability of power distribution. Changes in its level indicate time-periods of stable topography of power. RESULTS: The method was applied to data recorded in a psychological experiment related to cognitive processing under different emotional conditions elicited by words. Data were analysed in four frequency bands, specific to EEG signal: delta, theta, alpha and beta. Analysis of time course of the GFP in these bands allowed to indicate time periods of stable topography of power. CONCLUSIONS: This study shows that frequency enabled GFP may be used as a simple and intuitive tool for selecting time-frequency regions of interest, suitable for further statistical analysis.
8

Analysis of multichannel biomedical data

81%
Kaminski M., Zygierewicz J., Kus R., Crone N.
Acta Neurobiologiae Experimentalis
|
2005
|
tom 65
|
nr 4
9

Event-related desynchronization and synchronization in evoked K-complexes

71%
Zygierewicz J., Malinowska U., Suffczynski P., Piotrowski T., Durka P. J.
Acta Neurobiologiae Experimentalis
|
2009
|
tom 69
|
nr 2
254-261
K-complexes - phenomena occurring in sleep EEG - pose severe challenges in terms of detection as well as finding their physiological origin. In this study, K-complexes (KCs) were evoked by auditory stimuli delivered during sleep. The use of evoked KCs enables testing the sleeping nervous system under good experimental control. This paradigm allowed us to adopt into the KC studies a method of signal analysis that provides time-frequency maps of statistically significant changes in signal energy density. Our results indicate that KCs and sleep spindles may be organized by a slow oscillation. Accordingly, KCs might be evoked only if the stimulus occurs in a certain phase of the slow oscillation. We also observed middle-latency evoked responses following auditory stimulation in the last sleep cycle. This effect was revealed only by the time-frequency maps and was not visible in standard averages.
10

Recent advances in Brain-Computer Interfaces from braintech.pl

51%
Chabuda A., Dovgialo M., Rozanski P., Wieteska M., Pawlisz M., Duszyk A., Zygierewicz J., Rudkiewicz T., Durka P.
Acta Neurobiologiae Experimentalis
|
2018
|
tom 78
|
nr Suppl.1
Brain Computer Interface (BCI) is a system that al‑ lows communication without the mediation of muscles, using only brain waves. This technology passed from science-fiction to the laboratory decades ago, but real world applications, in fields from gaming and military to assistive technologies and consciousness assess‑ ment, are still operating at the proof of concept level. To change this landscape, building on a strong academic background, BrainTech Ltd. (http://braintech.pl) is pur‑ suing a project to create stable, robust, and usable BCI technologies, ready for the above mentioned real world applications. Software includes stable implementations of the major paradigms: P300 evoked potentials (visu‑ al and auditory), steady-state visual evoked potentials (SSVEP), and motor imagery. Features aimed at increas‑ ing productivity in both academic and practical appli‑ cations include the “BCI Control Panel”(*), which helps either the experimenter or caregiver in the setup and online control of the BCI session by displaying, for ex‑ ample, electrode impedances and online performance. Several indicators like accuracy or information transfer rate can be stored together with the signal, facilitating offline scientific analysis. Hardware systems include: (1) comfortable headcap with water-based electrodes, offering high quality signal without application of con‑ ducting gel, which normally requires washing hair after each EEG session, (2) 8-channel 24-bit wireless EEG am‑ plifier, offering online monitoring of electrode contacts and Gigaohm input impedance, either integrated into the headcap or offering connectors for standard EEG electrodes, (3) next generation of the “BCI Appliance”* – a dedicated hardware renderer for flexible stimuli for high-frequency SSVEP, first presented at CeBIT in 2012 as a base for the fastest BCI presented at this fair. (*“BCI Control Panel” and “BCI Appliance” are trademarks filed for protection to the Polish Patent Office). Demo of the discussed systems will be available in the presentation accompanying the Conference. The lecture will briefly discuss new research possibilities opened by the “BCI Appliance”, comfort of application of the novel EEG headcap, and facilitation of both real world BCI applica‑ tions and scientific research brought about by the pre‑ sented software.
11

Frequency specific changes in signal power and functional conectivity following stroke in the cat visual cortex

51%
Paulina Urban1, Andrzej Foik1, Anaida Ghazaryan1, Anna Popek1, Jan Jabłonka3, Ewa Kublik2, Maciek Kamiński4, Rafał Kuś4, Jarosław Żygierewicz4, Wioletta Waleszczyk1 P., Folk A., Ghazanyan A., Popek A., Jablonka J., Kublik E., Kaminski M., Kus R., Zygierewicz J., Waleszczyk W.
Acta Neurobiologiae Experimentalis
|
2015
|
tom 75
|
nr Supl.
AIM: The aim of the study wasto characterize early reorganization of cortical electrical activity within and around the stroke-affected area. METHODS: Photothrombotic stroke wasinduced in the visual cortex during the acute experiments in anaesthetized cats. The activity of neuronal populations (local field potential, LFP) were continuously monitored in the central region of the stroke, at the stroke border, and in the healthy tissue, up to three hours after stroke. In the offline analysis, using Welch and autoregressive parametric methods, we evaluated the changes in the frequency spectrum spanning from delta to gamma. Functional connectivity between cortical locations within and outside the stroke region was determined with Directed Transfer Function (DTF). Indirect and direct interactions in different frequency bands were determined by DTF and direct DTF, respectively. RESULTS: The stroke resulted in an overall decrease of the power within full frequency spectrum in the stroke affected region, but not outside this region, where an increase in the spectral power was observed. The most pronounced changes were observed three hours after the stroke. In one cat, we observed increase of the power in the stroke area in low frequency bands while the power in beta-gamma band was diminished. DTF and direct DTF revealed weakening of neuronal connections between the healthy tissue and the stroke region and a transient strengthening of local connections outside the stroke region. The earliest decrease in the strength of connections in stroke affected region was observed in high frequencies (beta and gamma). CONCLUSION: Stroke induce diverse effects in different frequency bands in both the LFP power spectrum and in the functional connectivity indicating complex influence on the neuronal activity within the stroke and in the vicinity of ischemic region. Supported by ERA-NET Neuron project REVIS.
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