scholarly journals Spectral fingerprints or spectral tilt? Evidence for distinct oscillatory signatures of memory formation

2018 ◽  
Author(s):  
Marie-Christin Fellner ◽  
Stephanie Gollwitzer ◽  
Stefan Rampp ◽  
Gernot Kreiselmeyr ◽  
Daniel Bush ◽  
...  
Keyword(s):  
Power Spectrum ◽  
High Frequency ◽  
Low Frequency ◽  
Brain Regions ◽  
Memory Formation ◽  
Memory Encoding ◽  
Frequency Bands ◽  
Theta Power ◽  
Gamma Power ◽  
Frequency Power

AbstractDecreases in low frequency power (2-30 Hz) alongside high frequency power increases (>40 Hz) have been demonstrated to predict successful memory formation. Parsimoniously this change in the frequency spectrum can be explained by one factor, a change in the tilt of the power spectrum (from steep to flat) indicating engaged brain regions. A competing view is that the change in the power spectrum contains several distinct brain oscillatory fingerprints, each serving different computations. Here, we contrast these two theories in a parallel MEG-intracranial EEG study where healthy participants and epilepsy patients, respectively, studied either familiar verbal material, or unfamiliar faces. We investigated whether modulations in specific frequency bands can be dissociated in time, space and by experimental manipulation. Both, MEG and iEEG data, show that decreases in alpha/beta power specifically predicted the encoding of words, but not faces, whereas increases in gamma power and decreases in theta power predicted memory formation irrespective of material. Critically, these different oscillatory signatures of memory encoding were evident in different brain regions. Moreover, high frequency gamma power increases occurred significantly earlier compared to low frequency theta power decreases. These results speak against a “spectral tilt” and demonstrate that brain oscillations in different frequency bands serve different functions for memory encoding.

scholarly journals Differential Effects of Isoflurane on High-frequency and Low-frequency γ Oscillations in the Cerebral Cortex and Hippocampus in Freely Moving Rats

2011 ◽  
Vol 114 (3) ◽  
pp. 588-595 ◽  
Author(s):  
Anthony G. Hudetz ◽  
Jeannette A. Vizuete ◽  
Siveshigan Pillay
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Brain Regions ◽  
Loss Of Consciousness ◽  
Dependent Manner ◽  
General Anesthetics ◽  
Frequency Bands ◽  
Depth Electrodes ◽  
Righting Reflex ◽  
40 Hz

Background Cortical γ oscillations are thought to play a role in conscious cognitive functions. Suppression of 40-Hz γ activity was implicated in the loss of consciousness during general anesthesia. However, several experimental studies found that γ oscillations were preserved in anesthesia. The authors investigated the concentration-dependent effect of isoflurane on spontaneous γ oscillations in two frequency bands and three distinct brain regions in the rat. Methods Adult Sprague-Dawley rats were chronically implanted with epidural and coaxial depth electrodes to record cortical field potentials in frontal cortex, visual cortex, and hippocampus in waking and at steady-state isoflurane concentrations of 0.4, 0.8, and 1.2%. The γ power was calculated for the frequency bands 30-50 and 70-140 Hz. Temporal variation and interregional synchrony of γ activity were analyzed using wavelet transform. Loss of consciousness was indexed by the loss of righting reflex. Results Rats lost their righting reflex at 0.8 ± 0.1% isoflurane. High-frequency γ power was decreased by isoflurane in a concentration-dependent manner (P < 0.001, 50% decrease at 0.8% isoflurane) in all brain regions. Low-frequency γ power was unaffected by isoflurane. The duration and interregional synchrony of high-frequency γ bursts was also reduced (P l < 0.001, 40% decrease at 0.8% isoflurane). Conclusions Distinction between high- and low-frequency γ bands is important when evaluating the effect of general anesthetics on brain electrical activity. Spontaneous 40-Hz γ power does not indicate the state of consciousness. The attenuation and interregional desynchronization of high-frequency γ oscillations appear to correlate with the loss of consciousness.

scholarly journals Bispectrum-based Cross-frequency Functional Connectivity: A Study of Alzheimer's Disease

2021 ◽  
Author(s):  
Dominik Klepl ◽  
Fei He ◽  
Min Wu ◽  
Daniel J Blackburn ◽  
Ptolemaios G Sarrigiannis
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Functional Connectivity ◽  
High Frequency ◽  
Neurodegenerative Disorder ◽  
Low Frequency ◽  
Brain Regions ◽  
Frequency Bands ◽  
Frequency Coupling ◽  
Eeg Recordings

Alzheimer's disease (AD) is a neurodegenerative disorder known to affect functional connectivity (FC) across many brain regions. Linear FC measures have been applied to study the differences in AD by splitting neurophysiological signals such as electroencephalography (EEG) recordings into discrete frequency bands and analysing them in isolation from each other. We address this limitation by quantifying cross-frequency FC in addition to the traditional within-band approach. Cross-bispectrum, a higher-order spectral analysis approach, is used to measure the nonlinear FC and is compared with the cross-spectrum, which only measures the linear FC within bands. This work reports the first use of cross-bispectrum to reconstruct a cross-frequency FC network where each frequency band is treated as a layer in a multilayer network with both inter- and intra-layer edges. An increase of within-band FC in AD is observed in low-frequency bands using both methods. Bispectrum also detects multiple cross-frequency differences, mainly increased FC in AD in delta-theta coupling. An increased importance of low-frequency coupling and decreased importance of high-frequency coupling is observed in AD. Integration properties of AD networks are more vulnerable than HC, while the segregation property is maintained in AD. Moreover, the segregation property of γ is less vulnerable in AD, suggesting the shift of importance from high-frequency activity towards low-frequency components. The results highlight the importance of studying nonlinearity and including cross-frequency FC in characterising AD. Moreover, the results demonstrate the advantages and limitations of using bispectrum to reconstruct FC networks.

scholarly journals Evaluating Acupuncture Point and Nonacupuncture Point Stimulation with EEG: A High-Frequency Power Spectrum Analysis

2016 ◽  
Vol 2016 ◽  
pp. 1-9 ◽  
Author(s):  
Kwang-Ho Choi ◽  
O. Sang Kwon ◽  
Seong Jin Cho ◽  
Sanghun Lee ◽  
Suk-Yun Kang ◽  
...  
Keyword(s):  
Power Spectrum ◽  
High Frequency ◽  
Acupuncture Point ◽  
High Frequency Power ◽  
Beta Power ◽  
Gamma Power ◽  
Sensory Responses ◽  
High Beta ◽  
Frequency Power Spectrum ◽  
Frequency Power

To identify physical and sensory responses to acupuncture point stimulation (APS), nonacupuncture point stimulation (NAPS) and no stimulation (NS), changes in the high-frequency power spectrum before and after stimulation were evaluated with electroencephalography (EEG). A total of 37 healthy subjects received APS at the LI4 point, NAPS, or NS with their eyes closed. Background brain waves were measured before, during, and after stimulation using 8 channels. Changes in the power spectra of gamma waves and high beta waves before, during, and after stimulation were comparatively analyzed. After NAPS, absolute high beta power (AHBP), relative high beta power (RHBP), absolute gamma power (AGP), and relative gamma power (RGP) tended to increase in all channels. But no consistent notable changes were found for APS and NS. NAPS is believed to cause temporary reactions to stress, tension, and sensory responses of the human body, while APS responds stably compared to stimulation of other parts of the body.

scholarly journals Kurtosis and skewness of high-frequency brain signals are altered in paediatric epilepsy

2020 ◽  
Vol 2 (1) ◽  
Author(s):  
Jing Xiang ◽  
Ellen Maue ◽  
Yuyin Fan ◽  
Lei Qi ◽  
Francesco T Mangano ◽  
...  
Keyword(s):  
High Frequency ◽  
Intractable Epilepsy ◽  
Low Frequency ◽  
Brain Regions ◽  
Control Group ◽  
Frequency Bands ◽  
Non Invasive ◽  
Brain Signals ◽  
Paediatric Epilepsy ◽  
Virtual Electrode

Abstract Intracranial studies provide solid evidence that high-frequency brain signals are a new biomarker for epilepsy. Unfortunately, epileptic (pathological) high-frequency signals can be intermingled with physiological high-frequency signals making these signals difficult to differentiate. Recent success in non-invasive detection of high-frequency brain signals opens a new avenue for distinguishing pathological from physiological high-frequency signals. The objective of the present study is to characterize pathological and physiological high-frequency signals at source levels by using kurtosis and skewness analyses. Twenty-three children with medically intractable epilepsy and age-/gender-matched healthy controls were studied using magnetoencephalography. Magnetoencephalographic data in three frequency bands, which included 2–80 Hz (the conventional low-frequency signals), 80–250 Hz (ripples) and 250–600 Hz (fast ripples), were analysed. The kurtosis and skewness of virtual electrode signals in eight brain regions, which included left/right frontal, temporal, parietal and occipital cortices, were calculated and analysed. Differences between epilepsy and controls were quantitatively compared for each cerebral lobe in each frequency band in terms of kurtosis and skewness measurements. Virtual electrode signals from clinical epileptogenic zones and brain areas outside of the epileptogenic zones were also compared with kurtosis and skewness analyses. Compared to controls, patients with epilepsy showed significant elevation in kurtosis and skewness of virtual electrode signals. The spatial and frequency patterns of the kurtosis and skewness of virtual electrode signals among the eight cerebral lobes in three frequency bands were also significantly different from that of the controls (2–80 Hz, P < 0.001; 80–250 Hz, P < 0.00001; 250–600 Hz, P < 0.0001). Compared to signals from non-epileptogenic zones, virtual electrode signals from epileptogenic zones showed significantly altered kurtosis and skewness (P < 0.001). Compared to normative data from the control group, aberrant virtual electrode signals were, for each patient, more pronounced in the epileptogenic lobes than in other lobes(kurtosis analysis of virtual electrode signals in 250–600 Hz; odds ratio = 27.9; P < 0.0001). The kurtosis values of virtual electrode signals in 80–250 and 250–600 Hz showed the highest sensitivity (88.23%) and specificity (89.09%) for revealing epileptogenic lobe, respectively. The combination of virtual electrode and kurtosis/skewness measurements provides a new quantitative approach to distinguishing pathological from physiological high-frequency signals for paediatric epilepsy. Non-invasive identification of pathological high-frequency signals may provide novel important information to guide clinical invasive recordings and direct surgical treatment of epilepsy.

scholarly journals Spectral tilt underlies mathematical problem solving

2019 ◽  
Author(s):  
Michael J. Randazzo ◽  
Youssef Ezzyat ◽  
Michael J. Kahana
Keyword(s):  
Problem Solving ◽  
Power Spectrum ◽  
High Frequency ◽  
Cognitive Task ◽  
Mathematical Problem ◽  
Low Frequency ◽  
Mathematical Problem Solving ◽  
Problem Solving Task ◽  
Frequency Power ◽  
Spectral Tilt

AbstractNeural activity associated with successful cognition appears as a tilt in the power spectrum of the local field potential, wherein increases in high-frequency power accompany decreases in low frequency power. Whereas this pattern has been shown in a wide range of memory tasks, it is unknown whether this increased spectral tilt reflects underlying memory-specific processes or rather a domain-general index of task engagement. To address the question of whether increased spectral tilt reflects increased attention to a cognitive task, we collected intracranial recordings from three hundred thirty neurosurgical patients as they performed a mathematical problem solving task. We used a mathematical problem solving task, because it allowed us to decouple task-specific processes with domain-general attention in a novel way. Using a statistical model to control for inherent problem complexity, we classified individual math problems based on whether a subject performed faster than predicted (high-attention or fast) or slower than predicted (low-attention, or slow) based on residual response times. In contrast to the domain-general attentional account, problems that took longer than predicted produced stronger evidence for the spectral tilt: widespread increases in high frequency (31–180 Hz) power and decreases in low frequency (3–17 Hz) power across frontal, temporal, and parietal cortices. The pattern emerged early within each trial and was sustained throughout the response period but was not observed in the medial temporal lobe. The data show that engaging in mathematical problem solving leads to a distributed spectral tilt pattern, even when accounting for variability in performance driven by the arithmetic demands of the problems themselves, and suggest that broadband changes in the power spectrum reflect an index of information processing in the brain beyond simple attention to the cognitive task.

Modulation of Neurocardiac Function by Oesophageal Stimulation in Humans

1997 ◽  
Vol 92 (2) ◽  
pp. 167-174 ◽  
Author(s):  
Gervais Tougas ◽  
Markad Kamath ◽  
Geena Watteel ◽  
Debbie Fitzpatrick ◽  
Ernest L. Fallen ◽  
...  
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
Power Spectrum ◽  
High Frequency ◽  
Low Frequency ◽  
Sensory Stimulation ◽  
Sensory Stimuli ◽  
Autonomic Reflexes ◽  
Low Frequency Power ◽  
Beat Heart

1. The heart and the oesophagus have similar sensory pathways, and sensations originating from the oesophagus are often difficult to differentiate from those of cardiac origin. We hypothesized that oesophageal sensory stimuli could alter neurocardiac function through autonomic reflexes elicited by these oesophageal stimuli. In the present study, we examined the neurocardiac response to oesophageal stimulation and the effects of electrical and mechanical oesophageal stimulation on the power spectrum of beat-to-beat heart rate variability in male volunteers. 2. In 14 healthy volunteers, beat-to-beat heart rate variability was compared at rest and during oesophageal stimulation, using either electrical (200 μs, 16 mA, 0.2 Hz) or mechanical (0.5 s, 14 ml, 0.2 Hz) stimuli. The power spectrum of beat-to-beat heart rate variability was obtained and its low- and high-frequency components were determined. 3. Distal oesophageal stimulation decreased heart rate slightly (both electrical and mechanical) (P < 0.005), and markedly altered heart rate variability (P < 0.001). Both electrical and mechanical oesophageal stimulation increased the absolute and normalized area of the high-frequency band within the power spectrum (P < 0.001), while simultaneously decreasing the low-frequency power (P < 0.005). 4. In humans, oesophageal stimulation, whether electrical or mechanical, appears to amplify respiratory-driven cardiac vagoafferent modulation while decreasing sympathetic modulation. The technique provides access to vagoafferent fibres and thus may yield useful information on the autonomic effects of visceral or oesophageal sensory stimulation.

Elevated heart rate variability in physically active postmenopausal women: a cardioprotective effect?

1996 ◽  
Vol 271 (2) ◽  
pp. H455-H460 ◽  
Author(s):  
K. P. Davy ◽  
N. L. Miniclier ◽  
J. A. Taylor ◽  
E. T. Stevenson ◽  
D. R. Seals
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
Postmenopausal Women ◽  
High Frequency ◽  
Low Frequency ◽  
Total Power ◽  
High Frequency Power ◽  
Fat Percentage ◽  
Physically Active ◽  
Frequency Power

Coronary heart disease (CHD) and cardiac sudden death (CSD) incidence accelerates after menopause, but the incidence is lower in physically active versus less active women. Low heart rate variability (HRV) is a risk factor for CHD and CSD. The purpose of the present investigation was to test the hypothesis that HRV at rest is greater in physically active compared with less active postmenopausal women. If true, we further hypothesized that the greater HRV in the physically active women would be closely associated with an elevated spontaneous cardiac baroreflex sensitivity (SBRS). HRV (both time and frequency domain measures) and SBRS (sequence method) were measured during 5-min periods of controlled frequency breathing (15 breaths/min) in the supine, sitting, and standing postures in 9 physically active postmenopausal women (age = 53 +/- 1 yr) and 11 age-matched controls (age = 56 +/- 2 yr). Body weight, body mass index, and body fat percentage were lower (P < 0.01) and maximal oxygen uptake was higher (P < 0.01) in the physically active group. The standard deviation of the R-R intervals (time domain measure) was higher in all postures in the active women (P < 0.05) as were the high-frequency, low-frequency, and total power of HRV. SBRS also was higher (P < 0.05) in the physically active women in all postures and accounted for approximately 70% of the variance in the high-frequency power of HRV (P < 0.05). The results of the present investigation indicate that physically active postmenopausal women demonstrate higher levels of HRV compared with age-matched, less active women. Furthermore, SBRS accounted for the majority of the variance in the high-frequency power of HRV, suggesting the possibility of a mechanistic link with cardiac vagal modulation of heart rate. Our findings may provide insight into a possible cardioprotective mechanism in physically active postmenopausal women.

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