scholarly journals Spectrum Degradation of Hippocampal LFP During Euthanasia

2021 ◽  
Vol 15 ◽  
Author(s):  
Yuchen Zhou ◽  
Alex Sheremet ◽  
Jack P. Kennedy ◽  
Nicholas M. DiCola ◽  
Carolina B. Maciel ◽  
...  
Keyword(s):  
Entorhinal Cortex ◽  
Fault Tolerant ◽  
Field Potential ◽  
Power Spectra ◽  
Direct Consequence ◽  
Synaptic Activity ◽  
Low Frequencies ◽  
Second Stage ◽  
Gamma Rhythm ◽  
Neural Entrainment

The hippocampal local field potential (LFP) exhibits a strong correlation with behavior. During rest, the theta rhythm is not prominent, but during active behavior, there are strong rhythms in the theta, theta harmonics, and gamma ranges. With increasing running velocity, theta, theta harmonics and gamma increase in power and in cross-frequency coupling, suggesting that neural entrainment is a direct consequence of the total excitatory input. While it is common to study the parametric range between the LFP and its complementing power spectra between deep rest and epochs of high running velocity, it is also possible to explore how the spectra degrades as the energy is completely quenched from the system. Specifically, it is unknown whether the 1/f slope is preserved as synaptic activity becomes diminished, as low frequencies are generated by large pools of neurons while higher frequencies comprise the activity of more local neuronal populations. To test this hypothesis, we examined rat LFPs recorded from the hippocampus and entorhinal cortex during barbiturate overdose euthanasia. Within the hippocampus, the initial stage entailed a quasi-stationary LFP state with a power-law feature in the power spectral density. In the second stage, there was a successive erosion of power from high- to low-frequencies in the second stage that continued until the only dominant remaining power was <20 Hz. This stage was followed by a rapid collapse of power spectrum toward the absolute electrothermal noise background. As the collapse of activity occurred later in hippocampus compared with medial entorhinal cortex, it suggests that the ability of a neural network to maintain the 1/f slope with decreasing energy is a function of general connectivity. Broadly, these data support the energy cascade theory where there is a cascade of energy from large cortical populations into smaller loops, such as those that supports the higher frequency gamma rhythm. As energy is pulled from the system, neural entrainment at gamma frequency (and higher) decline first. The larger loops, comprising a larger population, are fault-tolerant to a point capable of maintaining their activity before a final collapse.

scholarly journals Spectrum Degradation of Hippocampal LFP During Euthanasia

2020 ◽  
Author(s):  
Y. Zhou ◽  
A. Sheremet ◽  
J. P. Kennedy ◽  
Nicholas M. DiCola ◽  
Carolina B. Maciel ◽  
...  
Keyword(s):  
Entorhinal Cortex ◽  
Fault Tolerant ◽  
Field Potential ◽  
Power Spectra ◽  
Direct Consequence ◽  
Excitatory Input ◽  
Synaptic Activity ◽  
Low Frequencies ◽  
Gamma Rhythm ◽  
Neural Entrainment

AbstractThe hippocampal local field potential (LFP) exhibits a strong correlation with behavior. During rest, the theta rhythm is not prominent, but during active behavior, there are strong rhythms in the theta, theta harmonics, and gamma ranges. With increasing running velocity, theta, theta harmonics and gamma increase in power and in cross-frequency coupling, suggesting that neural entrainment is a direct consequence of the total excitatory input. While it is common to study the parametric range between the LFP and its complementing power spectra between deep rest and epochs of high running velocity, it is also possible to explore how the spectra degrades as the energy is completely quenched from the system. Specifically, it is unknown whether the 1/f slope is preserved as synaptic activity becomes diminished, as low frequencies are generated by large pools of neurons while higher frequencies comprise the activity of more local neuronal populations. To test this hypothesis, we examined rat LFPs recorded from the hippocampus and entorhinal cortex during barbiturate overdose euthanasia. Within the hippocampus, the initial stage entailed a quasi-stationary stage when the LFP spectrum exhibited power-law feature while the frequency components over 20 Hz exhibited a power decay with a similar decay rate. This stage was followed by a rapid collapse of power spectrum towards the absolute electrothermal noise background. As the collapse of activity occurred later in hippocampus compared with medial entorhinal cortex or visual cortex, it suggests that the ability of a neural network to maintain the 1/f slope with decreasing energy is a function of general connectivity. Broadly, these data support the energy cascade theory where there is a cascade of energy from large cortical populations into smaller loops, such as those that supports the higher frequency gamma rhythm. As energy is pulled from the system, neural entrainment at gamma frequency (and higher) decline first. The larger loops, comprising a larger population, are fault-tolerant to a point capable of maintaining their activity before a final collapse.

scholarly journals Altered low frequency brain rhythms precede changes in gamma power during tauopathy

2021 ◽  
Author(s):  
Fabio R Rodrigues ◽  
Amalia Papanikolaou ◽  
Joanna Holeniewska ◽  
Keith G Phillips ◽  
Aman B Saleem ◽  
...  
Keyword(s):  
Visual Stimulation ◽  
Brain Activity ◽  
Field Potential ◽  
Low Frequency ◽  
Wide Band ◽  
Low Frequencies ◽  
Brain Rhythms ◽  
Gamma Range ◽  
Gamma Rhythm ◽  
Gamma Rhythms

Alzheimer's disease and other dementias are associated with disruptions of electrophysiological brain activity, including low frequency and gamma rhythms. Many of these dementias are also associated with the malfunction of the membrane associated protein tau. Tauopathy disrupts neuronal function and the stability of synapses and is a key driver of neurodegeneration. Here we ask how brain rhythms are affected by tauopathy, at different stages of its progression. We performed local field potential recordings from visual cortex of rTg4510 and control animals at early stages of neurodegeneration (5 months) and at a more advanced stage where pathology is evident (8 months). We measured brain activity in the presence or absence of external visual stimulation, and while monitoring pupil diameter and locomotion to establish animal behavioural states. At 5 months, before substantial pathology, we found an increase in low frequency rhythms during resting state in tauopathic animals. This was because tauopathic animals entered intermittent periods of increased neural synchronisation, where activity across a wide band of low frequencies was strongly correlated. At 8 months, when the degeneration was more advanced, the increased synchronisation and low frequency power was accompanied by a reduction in power in the gamma range, with diverse effects across different components of the gamma rhythm. Our results indicate that slower rhythms are impaired earlier than gamma rhythms in tauopathy, suggesting that electrophysiological measurements can indicate both the presence and progression of tauopathic degeneration.

scholarly journals Phase of neuronal activity encodes 2-dimensional space in the human entorhinal cortex

2018 ◽  
Author(s):  
Zoltan Nadasdy ◽  
Ágoston Török ◽  
T. Peter Nguyen ◽  
Jason Y. Shen ◽  
Deborah E. Briggs ◽  
...  
Keyword(s):  
Entorhinal Cortex ◽  
Local Field ◽  
Cortical Neurons ◽  
Cell Activity ◽  
Field Potential ◽  
Gamma Oscillations ◽  
Spatial Modulation ◽  
Phase Dynamics ◽  
Gamma Rhythm ◽  
Phase Tuning

AbstractThe entorhinal cortex plays a vital role in our spatial awareness. Much focus has been placed on the spatial activity of its individual neurons, which fire in a grid-like pattern across an environment1. On a population level, however, neurons in the entorhinal cortex also display coherent rhythmic activity known as local field potential. These local field oscillations have been shown to correlate with behavioural states but it remains unclear how these oscillations relate to spatial behaviour and the spatial firing pattern of individual neurons. To investigate this, we recorded entorhinal cortical neurons in the human brain during spatial memory tasks performed in virtual environments. We observed a spatial modulation of the phase of action potentials relative to the local field potentials. In addition, the spike phase modulation displayed correlation with the movement of the avatar, displayed discrete phase tuning at the cellular level, rotated phase between electrodes, and expressed spatially coherent phase maps that scaled with the virtual environment. Using surrogate data, we demonstrated that spike phase coherence is dependent on the spatial phase dynamics of gamma oscillations. We argue that the spatial coordination of spike generation with gamma rhythm underlies the emergence of grid cell activity in the entorhinal cortex. These results shed a new light on the intricate interlacing between the spiking activity of neurons and local field oscillations in the brain.

scholarly journals Shape analysis of gamma rhythm supports a superlinear inhibitory regime in an inhibition-stabilized network

2021 ◽  
Author(s):  
R Krishnakumaran ◽  
Mohammed Raees ◽  
Supratim Ray
Keyword(s):  
Shape Analysis ◽  
Field Potential ◽  
Power Spectra ◽  
Phase Relationship ◽  
Gamma Oscillations ◽  
Linear Regime ◽  
Full Field ◽  
Gamma Rhythm ◽  
Additional Constraints ◽  
Operating Regimes

AbstractVisual inspection of stimulus-induced gamma oscillations (30-70 Hz) often reveals a non-sinusoidal shape. Such distortions are a hallmark of non-linear systems and are also observed in mean-field models of gamma oscillations. A thorough characterization of the shape of the gamma cycle can therefore provide additional constraints on the operating regime of such models. However, the gamma waveform has not been quantitatively characterized, partially because the first harmonic of gamma, which arises because of the non-sinusoidal nature of the signal, is typically weak and gets masked due to a broadband increase in power related to spiking. To address this, we recorded spikes and local field potential (LFP) from the primary visual cortex (V1) of two awake female macaques while presenting full-field gratings or iso-luminant chromatic hues that produced huge gamma oscillations with prominent peaks at harmonic frequencies in the power spectra. We found that gamma and its first harmonic always maintained a specific phase relationship, resulting in a distinctive shape with a sharp trough and a shallow peak. Interestingly, a Wilson-Cowan (WC) model operating in an inhibition stabilized mode could replicate the findings, but only when the inhibitory population operated in the super-linear regime, as predicted recently. However, another recently developed model of gamma that operates in a linear regime driven by stochastic noise failed to produce salient harmonics or the observed shape. Our results impose additional constraints on models that generate gamma oscillations and their operating regimes.Significance StatementGamma rhythm is not sinusoidal. Understanding these distortions could provide clues about the cortical network that generates the rhythm. Here, we use harmonic phase analysis to describe these waveforms quantitatively, and show that the gamma rhythm in macaque V1, during the presentation of fullscreen plain-hues and achromatic-gratings, has a signature arch-shaped waveform, despite the variation in power and frequency reported earlier. We further demonstrate using population rate models that the non-sinusoidal waveform is dependent on the operating domain of the system generating it. Consequently, shape analysis provides additional constraints on cortical models and their operating regimes.

scholarly journals A model of the CA1 field rhythms

2021 ◽  
Author(s):  
Mysin I.E.
Keyword(s):  
Entorhinal Cortex ◽  
Theta Rhythm ◽  
Field Potential ◽  
Medial Septum ◽  
Postsynaptic Potentials ◽  
Hippocampal Ca1 ◽  
Gamma Rhythm ◽  
Hippocampal Ca1 Field ◽  
Gamma Rhythms ◽  
Phase Amplitude

AbstractWe propose a model of the main rhythms in the hippocampal CA1 field: theta rhythm, slow, middle, and fast gamma rhythms, and ripples oscillations. We have based this on data obtained from animals behaving freely. We have considered the modes of neuronal discharges and the occurrence of local field potential (LFP) oscillations in the theta and non-theta states at different inputs from the CA3 field, the medial entorhinal cortex, and the medial septum. In our work, we tried to reproduce the main experimental phenomena about rhythms in the CA1 field: the coupling of neurons to the phase of rhythms, cross-rhythm phase-phase and phase-amplitude coupling. Using computational experiments, we have proved the hypothesis that the descending phase of the theta rhythm in the CA1 field is formed by the input from the CA3 field via the Shaffer collaterals, and the ascending phase of the theta rhythm is formed by the inhibitory postsynaptic potentials from CCK basket cells. The slow gamma rhythm is coupled to the descending phase of the theta rhythm, since it also depends on the arrival of the signal via the Shaffer collaterals. The middle gamma rhythm is formed by the excitatory postsynaptic potentials of the principal neurons of the third layer of the entorhinal cortex, corresponds to experimental data. We were able to unite in a single mathematical model several theoretical ideas about the mechanisms of rhythmic processes in the CA1 field of the hippocampus.

scholarly journals Psychosocial Crowding Stress-Induced Changes in Synaptic Transmission and Glutamate Receptor Expression in the Rat Frontal Cortex

Biomolecules ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 294
Author(s):  
Agnieszka Zelek-Molik ◽  
Bartosz Bobula ◽  
Anna Gądek-Michalska ◽  
Katarzyna Chorązka ◽  
Adam Bielawski ◽  
...  
Keyword(s):  
Frontal Cortex ◽  
Primary Motor Cortex ◽  
Interleukin 1 ◽  
Field Potential ◽  
Long Term Potentiation ◽  
Plasma Corticosterone ◽  
Receptor Expression ◽  
Synaptic Activity ◽  
Common Mechanism ◽  
Crowding Stress

This study demonstrates how exposure to psychosocial crowding stress (CS) for 3, 7, and 14 days affects glutamate synapse functioning and signal transduction in the frontal cortex (FC) of rats. CS effects on synaptic activity were evaluated in FC slices of the primary motor cortex (M1) by measuring field potential (FP) amplitude, paired-pulse ratio (PPR), and long-term potentiation (LTP). Protein expression of GluA1, GluN2B mGluR1a/5, VGLUT1, and VGLUT2 was assessed in FC by western blot. The body’s response to CS was evaluated by measuring body weight and the plasma level of plasma corticosterone (CORT), adrenocorticotropic hormone (ACTH), and interleukin 1 beta (IL1B). CS 3 14d increased FP and attenuated LTP in M1, while PPR was augmented in CS 14d. The expression of GluA1, GluN2B, and mGluR1a/5 was up-regulated in CS 3d and downregulated in CS 14d. VGLUTs expression tended to increase in CS 7d. The failure to blunt the effects of chronic CS on FP and LTP in M1 suggests the impairment of habituation mechanisms by psychosocial stressors. PPR augmented by chronic CS with increased VGLUTs level in the CS 7d indicates that prolonged CS exposure changed presynaptic signaling within the FC. The CS bidirectional profile of changes in glutamate receptors’ expression seems to be a common mechanism evoked by stress in the FC.

Facilitation at the Lobster Neuromuscular Junction: A Stimulus-Dependent Mobilization Model

1997 ◽  
Vol 78 (1) ◽  
pp. 417-428 ◽  
Author(s):  
Mary Kate Worden ◽  
Maria Bykhovskaia ◽  
John T. Hackett
Keyword(s):  
Neuromuscular Junction ◽  
Kinetic Equations ◽  
Nerve Impulse ◽  
Stimulation Frequency ◽  
Synaptic Activity ◽  
Quantal Content ◽  
Physiological Basis ◽  
Low Frequencies ◽  
Average Probability ◽  
Frequency Facilitation

Worden, Mary Kate, Maria Bykhovskaia, and John T. Hackett. Facilitation at the lobster neuromuscular junction: a stimulus-dependent mobilization model. J. Neurophysiol. 78: 417–428, 1997. Frequency facilitation is a process whereby neurosecretion increases as a function of stimulation frequency during repetitive synaptic activity. To examine the physiological basis underlying facilitation, we have estimated the frequency dependence of the synaptic parameters n (number of units capable of responding to a nerve impulse) and P (average probability of responding) at the lobster neuromuscular junction. Both n and P increase as a function of frequency, suggesting that the efficiency of quantal docking and quantal fusion is regulated by repetitive synaptic activity. In experiments in which facilitation is strong and quantal content does not saturate over the frequency range tested, the value of P saturates at low frequencies of stimulation, and increases in quantal content at higher frequencies of stimulation are due to an increase in n. Therefore the value of P does not limit facilitation. We propose that transmitter release is limited by the rates of quantal mobilization and demobilization, and that each excitatory stimulus causes additional mobilization of quanta to dock at the presynaptic release sites. In such a model the binomial parameter n will correspond to the number of quanta docked at the release sites and available for release. We have developed and solved kinetic equations that describe how the number of docked quanta changes as a function of time and of stimulation frequency. The stimulus-dependent mobilization model of facilitation predicts that the reciprocal value of the quantal content depends linearly on the reciprocal product of the stimulation frequency and the probability of release. Fits of the experimental data confirm the accuracy of this prediction, showing that the model proposed here quantitatively describes frequency facilitation. The model predicts that high rates of quantal demobilization will produce strong frequency facilitation.

Stimulation of the Parasubiculum Modulates Entorhinal Cortex Responses to Piriform Cortex Inputs In Vivo

2004 ◽  
Vol 92 (2) ◽  
pp. 1226-1235 ◽  
Author(s):  
Douglas A. Caruana ◽  
C. Andrew Chapman
Keyword(s):  
Entorhinal Cortex ◽  
Hippocampal Formation ◽  
Piriform Cortex ◽  
Current Source ◽  
Field Potential ◽  
Implanted Electrodes ◽  
Deep Layers ◽  
Negative Field ◽  
Stimulation Of

Although a major output of the hippocampal formation is from the subiculum to the deep layers of the entorhinal cortex, the parasubiculum projects to the superficial layers of the entorhinal cortex and may therefore modulate how the entorhinal cortex responds to sensory inputs from other cortical regions. Recordings at multiple depths in the entorhinal cortex were first used to characterize field potentials evoked by stimulation of the parasubiculum in urethan-anesthetized rats. Current source density analysis showed that a prominent surface-negative field potential component is generated by synaptic activation in layer II. The surface-negative field potential was also observed in rats with chronically implanted electrodes. The response was maintained during short stimulation trains of ≤125 Hz, suggesting that it is generated by activation of monosynaptic inputs to the entorhinal cortex. The piriform cortex also projects to layer II of the entorhinal cortex, and interactions between parasubicular and piriform cortex inputs were investigated using double-site stimulation tests. Simultaneous activation of parasubicular and piriform cortex inputs with high-intensity pulses resulted in smaller synaptic potentials than were expected on the basis of summing the individual responses, consistent with the termination of both pathways onto a common population of neurons. Paired-pulse tests were then used to assess the effect of parasubicular stimulation on responses to piriform cortex stimulation. Responses of the entorhinal cortex to piriform cortex inputs were inhibited when the parasubiculum was stimulated 5 ms earlier and were enhanced when the parasubiculum was stimulated 20–150 ms earlier. These results indicate that excitatory inputs to the entorhinal cortex from the parasubiculum may enhance the propagation of neuronal activation patterns into the hippocampal circuit by increasing the responsiveness of the entorhinal cortex to appropriately timed inputs.

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