Quantification of phase synchronization phenomena and their importance for verbal memory processes

Schack, Bärbel; Weiss, Sabine

doi:10.1007/s00422-005-0555-1

Cited by 80 publications

(52 citation statements)

References 39 publications

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“…To our knowledge, there are no previous data on synchronization with the MTL during WM. Using scalp EEG, effects of WM maintenance on neocortical synchronization were mainly found in the theta and alpha frequency ranges (Sarnthein et al, 1998;Sauseng et al, 2005a,b;Schack and Weiss, 2005;Mizuhara and Yamaguchi, 2007), consistent with the proposed role of thetaband activity for WM (Klimesch et al, 2005). This contrasts with the selective effects in higher-frequency ranges found in our data.…”

Section: Phase-synchronization Analysiscontrasting

confidence: 57%

Interactions between Medial Temporal Lobe, Prefrontal Cortex, and Inferior Temporal Regions during Visual Working Memory: A Combined Intracranial EEG and Functional Magnetic Resonance Imaging Study

Axmacher¹,

Schmitz²,

Wagner³

et al. 2008

J. Neurosci.

179

131

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It is a fundamental question whether the medial temporal lobe (MTL) supports only long-term memory encoding, or contributes to working memory (WM) processes as well. Recent data suggest that the MTL is activated whenever multiple items or item features are being maintained in WM. This may rely on interactions between the MTL or the prefrontal cortex (PFC) and content-specific areas in the inferior temporal (IT) cortex. Here, we investigated the neural mechanism through which the MTL, PFC, and IT cortex interact during WM maintenance. First, we quantified phase synchronization of intracranial EEG data in epilepsy patients with electrodes in both regions. Second, we used directional coupling analysis to study whether oscillatory activity in the IT cortex drives the MTL or vice versa. Finally, we investigated functional connectivity in functional magnetic resonance imaging data of healthy subjects with seeds in the MTL and PFC. With increasing load, EEG phase synchronization between the IT cortex and anterior parahippocampal gyrus and within the MTL increased. Coupling was bidirectional in all load conditions, but changed toward an increased top-down (anterior parahippocampal gyrus 3 IT) coupling in the high gamma range (51-75 Hz) with increasing load. Functional connectivity between the MTL seed and the visual association cortex increased with load, but activity within the MTL and the PFC correlated with fewer voxels, suggesting that more specific neural networks were engaged. These data indicate that WM for multiple items depends on an increased strength of top-down control of activity within the IT cortex by the MTL.

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Section: Phase-synchronization Analysiscontrasting

confidence: 57%

Interactions between Medial Temporal Lobe, Prefrontal Cortex, and Inferior Temporal Regions during Visual Working Memory: A Combined Intracranial EEG and Functional Magnetic Resonance Imaging Study

Axmacher¹,

Schmitz²,

Wagner³

et al. 2008

J. Neurosci.

179

131

View full text Add to dashboard Cite

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“…Other studies have shown an increase in theta power [48,49] after the target word onset in speech perception studies though with different auditory stimulus presentation approaches. Weiss and Rappelsberger [43] and Schack and Weiss [19] also reported an increase in theta coherence in response to recalled versus non-recalled German nouns although they do not seem to have subtracted the evoked response from data before coherence analyses. Also, a pairwise Wilcoxon signed-rank test on WS protocol showed that there was a significant decrease in the beta power for about 200-300 ms starting around 400 ms after the onset in the [13 30] Hz frequency band.…”

Section: Discussionmentioning

confidence: 99%

“…As mentioned before, there are a limited number of studies on the brain's response to normal speech such as words and sentences [10,12,13,11,19,20,21]. In addition, not all of these studies target the induced response but rather focus on the evoked response to these stimuli.…”

Section: Introductionmentioning

confidence: 99%

Induced activity in EEG in response to auditory stimulation

Hosseini

Bell

Wang

et al. 2015

Biomedical Signal Processing and Control

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The response of the brain to a sensory stimulus may present itself in the electroencephalogram (EEG) as evoked and/or induced activity. While the evoked response is given by peaks and troughs in the signal, time-locked and phase-locked to the stimuli, the induced response is time-but not phase-locked, and can be considered as an increase or a decrease in the power of EEG in a specific frequency band at a specific time range with regard to the stimulus onset. The induced response does not have the same phase following successive stimuli. It is believed that cognition and perception of a stimulus present themselves primarily as the induced response in the EEG. In this paper, the induced response of the brain to auditory speech stimuli is investigated and different approaches to detect induced activity are compared. It is shown that there is an increase in theta and delta power in response to words compared to the baseline, starting around 500 ms after their onset. During this time, there is also an increase in pairwise coherence between the posterior electrodes. In response to tone bursts, a change in pairwise coherence was observed in the beta band starting around 200 ms. To the best of our knowledge, this is the first time such responses have been described using simple protocols without complex stimulus manipulations being involved. Responses in the EEG to speech rather than the more conventional tone-bursts or clicks suggests that it may be feasible to use the EEG as an objective means to demonstrate brain activation to salient real world stimuli. This would be of particular benefit in investigating access to speech in patients who are unable or unwilling to reliably respond to conventional subjective experimental protocols, such as infants.

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“…The original idea was to compare two signals by first separating their instantaneous amplitude from instantaneous phase information and then compare only phase time series. This is achieved by converting the real signal into its complex analytic version (Boashash, 1992) with signal processing techniques, like the Hilbert transform, Gabor expansion, or Wavelet filtering (for comparisons see Le Van Quyen et al, 2001;Schack and Weiss, 2005;Sun and Small, 2009). …”

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confidence: 99%

Functional Magnetic Resonance Imaging Phase Synchronization as a Measure of Dynamic Functional Connectivity

et al. 2012

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Functional brain activity and connectivity have been studied by calculating intersubject and seed-based correlations of hemodynamic data acquired with functional magnetic resonance imaging (fMRI). To inspect temporal dynamics, these correlation measures have been calculated over sliding time windows with necessary restrictions on the length of the temporal window that compromises the temporal resolution. Here, we show that it is possible to increase temporal resolution by using instantaneous phase synchronization (PS) as a measure of dynamic (time-varying) functional connectivity. We applied PS on an fMRI dataset obtained while 12 healthy volunteers watched a feature film. Narrow frequency band (0.04-0.07 Hz) was used in the PS analysis to avoid artifactual results. We defined three metrics for computing time-varying functional connectivity and time-varying intersubject reliability based on estimation of instantaneous PS across the subjects: (1) seed-based PS, (2) intersubject PS, and (3) intersubject seed-based PS. Our findings show that these PS-based metrics yield results consistent with both seed-based correlation and intersubject correlation methods when inspected over the whole time series, but provide an important advantage of maximal single-TR temporal resolution. These metrics can be applied both in studies with complex naturalistic stimuli (e.g., watching a movie or listening to music in the MRI scanner) and more controlled (e.g., event-related or blocked design) paradigms. A MATLAB toolbox FUNPSY (http://becs .aalto.fi/bml/software.html) is openly available for using these metrics in fMRI data analysis.

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Quantification of phase synchronization phenomena and their importance for verbal memory processes

Cited by 80 publications

References 39 publications

Interactions between Medial Temporal Lobe, Prefrontal Cortex, and Inferior Temporal Regions during Visual Working Memory: A Combined Intracranial EEG and Functional Magnetic Resonance Imaging Study

Interactions between Medial Temporal Lobe, Prefrontal Cortex, and Inferior Temporal Regions during Visual Working Memory: A Combined Intracranial EEG and Functional Magnetic Resonance Imaging Study

Induced activity in EEG in response to auditory stimulation

Functional Magnetic Resonance Imaging Phase Synchronization as a Measure of Dynamic Functional Connectivity

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