Theta- and gamma-band oscillatory uncoupling in the macaque hippocampus

Nested hippocampal oscillations in the rodent gives rise to temporal coding that may underlie learning, memory, and decision making. Theta/gamma coupling in rodent CA1 occurs during exploration and sharp-wave ripples during quiescence. Whether these oscillatory regimes extend to primates is less clear. We therefore sought to identify correspondences in frequency bands, nesting, and behavioral coupling taken from macaque hippocampus. We found that, in contrast to the rodent, theta and gamma frequency bands in macaque CA1 were segregated by behavioral states. Beta/gamma (15-70Hz) had greater power during visual search while theta (7-10 Hz) dominated during quiescence. Moreover, delta/theta (3-8 Hz) amplitude was strongest when beta2/slow gamma (20-35 Hz) amplitude was weakest, though the low frequencies coupled with higher, ripple frequencies (60-150 Hz). The distribution of spike-field coherence revealed three peaks matching the 3-10 Hz, 20-30 Hz and 60-150 Hz bands; however, the low frequency effects were primarily due to sharp-wave ripples. Accordingly, no intrinsic theta spiking rhythmicity was apparent. These results support a role for beta2/slow gamma modulation in CA1 during active exploration in the primate that is decoupled from theta oscillations. These findings diverge from the rodent oscillatory canon and call for a shift in focus and frequency when considering the primate hippocampus.

Download Full-text

Low Frequency Oscillations drive EEG's complexity changes during wakefulness and sleep

10.1101/2021.12.16.472983 ◽

2021 ◽

Author(s):

Joaquin Gonzalez ◽

Diego M. Mateos ◽

Matias Cavelli ◽

Alejandra Mondino ◽

Claudia Pascovich ◽

...

Keyword(s):

Slow Wave Sleep ◽

Low Frequency ◽

Neuronal Population ◽

Complexity Measures ◽

Low Frequencies ◽

New Approach ◽

Frequency Bands ◽

Cortical Oscillations ◽

Brain Signals ◽

Low Frequency Oscillations

Recently, the sleep-wake states have been analysed using novel complexity measures, complementing the classical analysis of EEGs by frequency bands. This new approach consistently shows a decrease in EEG's complexity during slow-wave sleep, yet it is unclear how cortical oscillations shape these complexity variations. In this work, we analyse how the frequency content of brain signals affects the complexity estimates in freely moving rats. We find that the low-frequency spectrum - including the Delta, Theta, and Sigma frequency bands - drives the complexity changes during the sleep-wake states. This happens because low-frequency oscillations emerge from neuronal population patterns, as we show by recovering the complexity variations during the sleep-wake cycle from micro, meso, and macroscopic recordings. Moreover, we find that the lower frequencies reveal synchronisation patterns across the neocortex, such as a sensory-motor decoupling that happens during REM sleep. Overall, our works shows that EEG's low frequencies are critical in shaping the sleep-wake states' complexity across cortical scales.

Download Full-text

Abnormalities of Alpha Activity in Frontocentral Region of the Brain as a Biomarker to Diagnose Adolescents With Bipolar Disorder

Clinical EEG and Neuroscience ◽

10.1177/1550059418824824 ◽

2019 ◽

Vol 50 (5) ◽

pp. 311-318 ◽

Cited By ~ 1

Author(s):

Ali Khaleghi ◽

Mohammad Reza Mohammadi ◽

Mahdi Moeini ◽

Hadi Zarafshan ◽

Mahbod Fadaei Fooladi

Keyword(s):

Bipolar Disorder ◽

Depressive Episode ◽

Spectral Power ◽

Low Frequency ◽

Alpha Power ◽

K Nearest Neighbors ◽

Frequency Bands ◽

Gamma Frequency ◽

Alpha Oscillation ◽

Depressive Episodes

Objectives. To investigate brain abnormalities in adolescents with new-onset bipolar disorder (BD) during acute hypomanic and depressive episodes using electroencephalogram (EEG) analysis and to derive a computer-based method for diagnosis of the disorder. Methods. EEG spectral power and entropy of 21 adolescents with BD (included 11 patients in the hypomanic episode and 10 patients in the depressive episode) and 18 healthy adolescents were compared. Moreover, using significant differences and K-nearest-neighbors (KNN) classifier, it was attempted to distinguish the BD adolescents from normal ones. Results. The BD adolescents had higher values of spectral power in all frequency bands, particularly in the frontocentral, mid-temporal, and right parietal regions. Also, spectral entropy had significantly increased in delta, alpha, and gamma frequency bands for BD. A high accuracy of 95.8% was achieved by all significant differences in the alpha band in discriminating adolescents with BD. The depressive state showed higher values of spectral power and entropy in low-frequency bands (delta and theta) compared to the hypomanic state. Conclusion. Based on BD symptoms, especially inattention, increased alpha power is a rational finding which is associated with thalamus dysfunction. Thus, it seems that EEG alpha oscillation is the main source of abnormality in BD. Furthermore, EEG slowing in the depressive episode is related to inhibition of electrical activity and reduced cognitive functions.

Download Full-text

Enhancement of phase-locking in rodents. I. An axonal recording study in gerbil

Journal of Neurophysiology ◽

10.1152/jn.00194.2016 ◽

2017 ◽

Vol 118 (4) ◽

pp. 2009-2023 ◽

Cited By ~ 5

Author(s):

Liting Wei ◽

Shotaro Karino ◽

Eric Verschooten ◽

Philip X. Joris

Keyword(s):

Cochlear Nucleus ◽

Phase Locking ◽

Low Frequency ◽

Small Animal ◽

Auditory Pathway ◽

Temporal Coding ◽

Superior Olivary Complex ◽

Low Frequencies ◽

Medial Nucleus ◽

Firing Properties

The trapezoid body (TB) contains axons of neurons in the anteroventral cochlear nucleus projecting to monaural and binaural nuclei in the superior olivary complex (SOC). Characterization of these monaural inputs is important for the interpretation of response properties of SOC neurons. In particular, understanding of the sensitivity to interaural time differences (ITDs) in neurons of the medial and lateral superior olive requires knowledge of the temporal firing properties of the monaural excitatory and inhibitory inputs to these neurons. In recent years, studies of ITD sensitivity of SOC neurons have made increasing use of small animal models with good low-frequency hearing, particularly the gerbil. We presented stimuli as used in binaural studies to monaural neurons in the TB and studied their temporal coding. We found that general trends as have been described in the cat are present in gerbil, but with some important differences. Phase-locking to pure tones tends to be higher in TB axons and in neurons of the medial nucleus of the TB (MNTB) than in the auditory nerve for neurons with characteristic frequencies (CFs) below 1 kHz, but this enhancement is quantitatively more modest than in cat. Stronger enhancement is common when TB neurons are stimulated at low frequencies below CF. It is rare for TB neurons in gerbil to entrain to low-frequency stimuli, i.e., to discharge a well-timed spike on every stimulus cycle. Also, complex phase-locking behavior, with multiple modes of increased firing probability per stimulus cycle, is common in response to low frequencies below CF. NEW & NOTEWORTHY Phase-locking is an important property of neurons in the early auditory pathway: it is critical for the sensitivity to time differences between the two ears enabling spatial hearing. Studies in cat have shown an improvement in phase-locking from the peripheral to the central auditory nervous system. We recorded from axons in an output tract of the cochlear nucleus and show that a similar but more limited form of temporal enhancement is present in gerbil.

Download Full-text

Real Ear Sound Pressure Levels Developed by Three Portable Stereo System Earphones

American Journal of Audiology ◽

10.1044/1059-0889.0104.52 ◽

1992 ◽

Vol 1 (4) ◽

pp. 52-55 ◽

Cited By ~ 4

Author(s):

Gail L. MacLean ◽

Andrew Stuart ◽

Robert Stenstrom

Keyword(s):

High Frequency ◽

Sound Pressure ◽

Low Frequency ◽

Test System ◽

Output Frequency ◽

Frequency Effects ◽

Adult Men ◽

Frequency Responses ◽

Significant Difference ◽

Sound Pressure Levels

Differences in real ear sound pressure levels (SPLs) with three portable stereo system (PSS) earphones (supraaural [Sony Model MDR-44], semiaural [Sony Model MDR-A15L], and insert [Sony Model MDR-E225]) were investigated. Twelve adult men served as subjects. Frequency response, high frequency average (HFA) output, peak output, peak output frequency, and overall RMS output for each PSS earphone were obtained with a probe tube microphone system (Fonix 6500 Hearing Aid Test System). Results indicated a significant difference in mean RMS outputs with nonsignificant differences in mean HFA outputs, peak outputs, and peak output frequencies among PSS earphones. Differences in mean overall RMS outputs were attributed to differences in low-frequency effects that were observed among the frequency responses of the three PSS earphones. It is suggested that one cannot assume equivalent real ear SPLs, with equivalent inputs, among different styles of PSS earphones.

Download Full-text

Faculty Opinions recommendation of Low-frequency theta oscillations in the human hippocampus during real-world and virtual navigation.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.727303818.793528735 ◽

2017 ◽

Author(s):

James Knierim

Keyword(s):

Real World ◽

Low Frequency ◽

Theta Oscillations ◽

Virtual Navigation ◽

Human Hippocampus

Download Full-text

Earless toads sense low frequencies but miss the high notes

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2017.1670 ◽

2017 ◽

Vol 284 (1864) ◽

pp. 20171670 ◽

Cited By ~ 10

Author(s):

Molly C. Womack ◽

Jakob Christensen-Dalsgaard ◽

Luis A. Coloma ◽

Juan C. Chaparro ◽

Kim L. Hoke

Keyword(s):

High Frequency ◽

Species Differences ◽

Low Frequency ◽

Auditory Brainstem ◽

Low Frequencies ◽

Hearing Sensitivity ◽

Sensory Pathways ◽

Airborne Sound ◽

Vibrational Sensitivity ◽

Species Specific

Sensory losses or reductions are frequently attributed to relaxed selection. However, anuran species have lost tympanic middle ears many times, despite anurans' use of acoustic communication and the benefit of middle ears for hearing airborne sound. Here we determine whether pre-existing alternative sensory pathways enable anurans lacking tympanic middle ears (termed earless anurans) to hear airborne sound as well as eared species or to better sense vibrations in the environment. We used auditory brainstem recordings to compare hearing and vibrational sensitivity among 10 species (six eared, four earless) within the Neotropical true toad family (Bufonidae). We found that species lacking middle ears are less sensitive to high-frequency sounds, however, low-frequency hearing and vibrational sensitivity are equivalent between eared and earless species. Furthermore, extratympanic hearing sensitivity varies among earless species, highlighting potential species differences in extratympanic hearing mechanisms. We argue that ancestral bufonids may have sufficient extratympanic hearing and vibrational sensitivity such that earless lineages tolerated the loss of high frequency hearing sensitivity by adopting species-specific behavioural strategies to detect conspecifics, predators and prey.

Download Full-text

A waveform inversion technique for measuring elastic wave attenuation in cylindrical bars

Geophysics ◽

10.1190/1.1443299 ◽

1992 ◽

Vol 57 (6) ◽

pp. 854-859 ◽

Cited By ~ 6

Author(s):

Xiao Ming Tang

Keyword(s):

Elastic Wave ◽

Wave Attenuation ◽

Waveform Inversion ◽

Finite Size ◽

Low Frequency ◽

Frequency Range ◽

Multiple Reflections ◽

Low Frequencies ◽

The Time Domain ◽

Attenuation Values

A new technique for measuring elastic wave attenuation in the frequency range of 10–150 kHz consists of measuring low‐frequency waveforms using two cylindrical bars of the same material but of different lengths. The attenuation is obtained through two steps. In the first, the waveform measured within the shorter bar is propagated to the length of the longer bar, and the distortion of the waveform due to the dispersion effect of the cylindrical waveguide is compensated. The second step is the inversion for the attenuation or Q of the bar material by minimizing the difference between the waveform propagated from the shorter bar and the waveform measured within the longer bar. The waveform inversion is performed in the time domain, and the waveforms can be appropriately truncated to avoid multiple reflections due to the finite size of the (shorter) sample, allowing attenuation to be measured at long wavelengths or low frequencies. The frequency range in which this technique operates fills the gap between the resonant bar measurement (∼10 kHz) and ultrasonic measurement (∼100–1000 kHz). By using the technique, attenuation values in a PVC (a highly attenuative) material and in Sierra White granite were measured in the frequency range of 40–140 kHz. The obtained attenuation values for the two materials are found to be reliable and consistent.

Download Full-text

Methods to isolate retrograde and prograde Rayleigh-wave signals

Geophysical Journal International ◽

10.1093/gji/ggz341 ◽

2019 ◽

Vol 219 (2) ◽

pp. 975-994 ◽

Cited By ~ 1

Author(s):

Gabriel Gribler ◽

T Dylan Mikesell

Keyword(s):

Rayleigh Wave ◽

Time Domain ◽

Fundamental Mode ◽

Poisson Ratio ◽

Low Frequency ◽

Wave Dispersion ◽

Low Frequencies ◽

Retrograde Motion ◽

Mode Identification ◽

Time Frequency

SUMMARY Estimating shear wave velocity with depth from Rayleigh-wave dispersion data is limited by the accuracy of fundamental and higher mode identification and characterization. In many cases, the fundamental mode signal propagates exclusively in retrograde motion, while higher modes propagate in prograde motion. It has previously been shown that differences in particle motion can be identified with multicomponent recordings and used to separate prograde from retrograde signals. Here we explore the domain of existence of prograde motion of the fundamental mode, arising from a combination of two conditions: (1) a shallow, high-impedance contrast and (2) a high Poisson ratio material. We present solutions to isolate fundamental and higher mode signals using multicomponent recordings. Previously, a time-domain polarity mute was used with limited success due to the overlap in the time domain of fundamental and higher mode signals at low frequencies. We present several new approaches to overcome this low-frequency obstacle, all of which utilize the different particle motions of retrograde and prograde signals. First, the Hilbert transform is used to phase shift one component by 90° prior to summation or subtraction of the other component. This enhances either retrograde or prograde motion and can increase the mode amplitude. Secondly, we present a new time–frequency domain polarity mute to separate retrograde and prograde signals. We demonstrate these methods with synthetic and field data to highlight the improvements to dispersion images and the resulting dispersion curve extraction.

Download Full-text

Spillovers of Stock Markets among the BRICS: New Evidence in Time and Frequency Domains before the Outbreak of COVID-19 Pandemic

Journal of Risk and Financial Management ◽

10.3390/jrfm14030112 ◽

2021 ◽

Vol 14 (3) ◽

pp. 112

Author(s):

Kai Shi

Keyword(s):

Stock Market ◽

Frequency Band ◽

Stock Markets ◽

Emerging Market ◽

Low Frequency ◽

Systematic Risk ◽

Error Variance ◽

Frequency Bands ◽

Volatility Spillovers ◽

Risk Sources

We attempted to comprehensively decode the connectedness among the abbreviation of five emerging market countries (BRICS) stock markets between 1 August 2002 and 31 December 2019 not only in time domain but also in frequency domain. A continuously varying spillover index based on forecasting error variance decomposition within a generalized abbreviation of vector-autoregression (VAR) framework was computed. With the help of spectral representation, heterogeneous frequency responses to shocks were separated into frequency-specific spillovers in five different frequency bands to reveal differentiated linkages among BRICS markets. Rolling sample analyses were introduced to allow for multiple changes during the sample period. It is found that return spillovers dominated by the high frequency band (within 1 week) part declined with the drop of frequencies, while volatility spillovers dominated by the low frequency band (above 1 quarter) part grew with the decline in frequencies; the dynamics of spillovers were influenced by crucial systematic risk events, and some similarities implied in the spillover dynamics in different frequency bands were found. From the perspective of identifying systematic risk sources, China’s stock market and Russia’s stock market, respectively, played an influential role for return spillover and volatility spillover across BRICS markets.

Download Full-text