scholarly journals Are sleep spindles poised on supercritical Hopf bifurcations?

2019 ◽  
Author(s):  
M. Ospeck
Keyword(s):  
Resting State ◽  
Underlying Mechanism ◽  
Frequency Selectivity ◽  
Long Term Memory ◽  
Sleep Spindles ◽  
Calcium Conductance ◽  
Sinusoidal Input ◽  
Low Threshold ◽  
Spike Bursts ◽  
Relay Neurons

ABSTRACTSleep spindles are recognized as an important intermediate state of long term memory formation. During non REM sleep, large numbers of thalamic relay neurons synchronize their spike bursts for one half to two seconds, entraining many millions of neurons, and constituting a sleep spindle. Here we study spindle amplification, entrainment, synchronization and decay. Relay neurons have both a high resting state near −60 millivolts (mV) and low resting state near −75 mV. Due to the neuron’s sodium conductance, low-threshold calcium conductance, and calcium-dependent H conductance, it exhibits a number of bifurcations, like its supercritical Hopf at −61 mV. Here low-threshold calcium conductance destabilizes membrane potential to birth a small limit-cycle in the 7-16 Hz range. Supercritical Hopfbifurcations are the underlying mechanism for amplification and frequency selectivity in hearing: hair cells are forced by sinusoidal input currents driving their mainly capacitive loads, with the forcing currents locking at 90 degree phase leads with respect to their oscillating membrane potentials. Here we model a small part of a spindle, with 6 cross-coupled relay neurons all poised on Hopfbifurcations. One neuron is forced by a weak noisy train of periodic current impulses that typically lock at a 90 degree phase lead with respect to its voltage oscillation. It then drives its neighbors, causing them to drive each other at much smaller phase angles, usually less than ±10 degrees. The system of Hopf oscillators exhibit small signal amplification and frequency selectivity, high degrees of synchronization and noise rejection, and switch-ability. These argue in favor of spindling relay neurons poising on, or very near to, supercritical Hopfbifurcations. Also, during the phase-locking of their spike bursts, calcium conductance oscillations increase internal calcium, which turns on slow H current. This depolarizes the relay cells, pushing them below their Hopfbifurcations and terminating the spindle.

Subthreshold frequency selectivity in avian auditory thalamus

1994 ◽  
Vol 71 (4) ◽  
pp. 1361-1372 ◽  
Author(s):  
B. Strohmann ◽  
D. W. Schwarz ◽  
E. Puil
Keyword(s):  
Frequency Selectivity ◽  
Membrane Properties ◽  
Resting Potential ◽  
Resonant Peak ◽  
Auditory Signal ◽  
Voltage Response ◽  
Potential Range ◽  
Na Current ◽  
Frequency Responses ◽  
Low Threshold

1. We studied the frequency responses of neurons in the nucleus ovoidalis (OV), the principal thalamic auditory relay nucleus of the chicken, in the subthreshold range of membrane potentials. The frequency response is the impedance amplitude profile evident in the voltage response to a broadband stimulus. The stimulus was a deterministic periodic current input of small amplitude, sweeping through a specified frequency range. We used whole-cell, tight-seal recording techniques in slices to study the voltage responses and membrane properties in current and voltage clamp. 2. Generally, low-frequency resonant humps with peak impedances of approximately 6 Hz characterized the frequency responses of OV neurons. This resonance was the principal determinant for frequency selectivity in the majority of OV neurons expressing only a tonic mode of firing. 3. The 6-Hz resonance was voltage dependent and most distinct where the activation ranges of a hyperpolarization activated inward current (IH) and a persistent Na+ current tend to overlap. The potential range for optimal resonance often included the resting potential. 4. Application of the Na+ current antagonist, tetrodotoxin, blocked the persistent Na+ current and most of the resonant hump at depolarized levels but did not affect the resonant peak along the frequency axis. Thus the persistent Na+ current may serve to amplify the resonance. 5. Extracellular application of Cs+, but not Ba2+, blocked a voltage sag during pulsed hyperpolarization as well as the IH current. Application of Cs+ also eliminated the 6-Hz resonance. An IH seems, therefore, instrumental for the resonance. 6. A minority of neurons that expressed low-threshold Ca2+ spikes and burst firing at hyperpolarized states displayed voltage oscillations at 2-4 Hz, spontaneously or in response to pulsatile stimuli. Application of Ni2+ blocked the oscillations and the low-threshold spikes, presumably produced by a T-type Ca2+ current. The resonance at 6 Hz, however, was only slightly affected by Ni2+. A T-type current, therefore, is critical for the 2- to 4-Hz oscillations. 7. Membrane resonance may dominate the power spectrum of subthreshold potential fluctuations. The resonance demonstrated in vitro may be stabilized by experimental procedures; its frequency may be different and more variable in vivo. Resonances in thalamic neurons may play a role in auditory signal processing in birds.

scholarly journals Low–threshold calcium spike bursts in the human thalamus

Brain ◽  
1996 ◽  
Vol 119 (2) ◽  
pp. 363-375 ◽  
Author(s):  
D. Jeanmonod ◽  
M. Magnin ◽  
A. Morel
Keyword(s):  
Human Thalamus ◽  
Low Threshold ◽  
Spike Bursts

scholarly journals Resting State fMRI: A Valuable Tool for Studying Cognitive Dysfunction in PD

2018 ◽  
Vol 2018 ◽  
pp. 1-5 ◽  
Author(s):  
Kai Li ◽  
Wen Su ◽  
Shu-Hua Li ◽  
Ying Jin ◽  
Hai-Bo Chen
Keyword(s):  
Cognitive Impairment ◽  
Cognitive Dysfunction ◽  
Cognitive Deficits ◽  
Resting State ◽  
Lewy Bodies ◽  
Resting State Fmri ◽  
Underlying Mechanism ◽  
Research Field ◽  
Functional Magnetic Resonance ◽  
Positron Emission

Cognitive impairment is a common disabling symptom in PD. Unlike motor symptoms, the mechanism underlying cognitive dysfunction in Parkinson’s disease (PD) remains unclear and may involve multiple pathophysiological processes. Resting state functional magnetic resonance imaging (rs-fMRI) is a fast-developing research field, and its application in cognitive impairments in PD is rapidly growing. In this review, we summarize rs-fMRI studies on cognitive function in PD and discuss the strong potential of rs-fMRI in this area. rs-fMRI can help reveal the pathophysiology of cognitive symptoms in PD, facilitate early identification of PD patients with cognitive impairment, distinguish PD dementia from dementia with Lewy bodies, and monitor and guide treatment for cognitive impairment in PD. In particular, ongoing and future longitudinal studies would enhance the ability of rs-fMRI in predicting PD dementia. In combination with other modalities such as positron emission tomography, rs-fMRI could give us more information on the underlying mechanism of cognitive deficits in PD.

Transient enhancement of low-threshold calcium current in thalamic relay neurons after corticectomy

1993 ◽  
Vol 70 (1) ◽  
pp. 20-27 ◽  
Author(s):  
J. M. Chung ◽  
J. R. Huguenard ◽  
D. A. Prince
Keyword(s):  
Calcium Currents ◽  
High Threshold ◽  
Pharmacological Properties ◽  
Current Time ◽  
Cortical Ablation ◽  
Thalamic Relay ◽  
Low Threshold ◽  
Small Change ◽  
Thalamic Relay Neurons ◽  
Relay Neurons

1. The alterations of voltage-sensitive calcium currents produced in thalamic cells by injury were investigated under voltage clamp using patch-clamp recordings in the whole-cell configuration. 2. One day after unilateral cortical ablation in immature rats (postnatal day 7), low-threshold transient calcium (T) currents in acutely isolated thalamic relay neurons (RNs) were increased by 68% compared with contralateral controls (P < 0.001). Three days after the operation, T currents in injured neurons were at 44% of control levels (P < 0.001). On the other hand, high-threshold (L) calcium currents in RNs did not change over the same interval. 3. To investigate the mechanism for the increase of T current, both kinetics and voltage dependency of activation and inactivation were examined. At a test voltage of -40 mV, the activation time constant decreased from 4.1 to 3.2 ms (P < 0.05); however, this small change was insufficient to explain the large increase in T current. Time constants for both fast and slow inactivation did not change significantly, nor did voltage dependence of activation or inactivation of thalamic T currents. 4. Methyl-phenyl-succinimide (MPS, 1 mM), a compound known to block T currents, was used to examine possible alterations in the pharmacological properties of T channels after injury. MPS was more effective in reducing T currents in normal versus injured RNs (24 and 20% reductions, respectively; P < 0.05), suggesting that pharmacological properties of T channels in the injured RNs may be different from those of the normal RNs.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased Synchrony with Increase of a Low-Threshold Calcium Conductance in a Model Thalamic Network: A Phase-Shift Mechanism

2000 ◽  
Vol 12 (7) ◽  
pp. 1553-1571 ◽  
Author(s):  
Elizabeth Thomas ◽  
Thierry Grisar
Keyword(s):  
Phase Shift ◽  
Computer Model ◽  
Calcium Current ◽  
Epileptic Activity ◽  
Absence Epilepsy ◽  
Similar Increase ◽  
Calcium Conductance ◽  
Synchronous Firing ◽  
Low Threshold Spike ◽  
Low Threshold

A computer model of a thalamic network was used in order to examine the effects of an isolated augmentation in a low-threshold calcium current. Such an isolated augmentation has been observed in the reticular thalamic (RE) nucleus of the genetic absence epilepsy rat from the Strasbourg (GAERS) model of absence epilepsy. An augmentation of the low-threshold calcium conductance in the RE neurons (gTs) of the model thalamic network was found to lead to an increase in the synchronized firing of the network. This supports the hypothesis that the isolated increase in gTs may be responsible for epileptic activity in the GAERS rat. The increase of gTs in the RE neurons led to a slight increase in the period of the isolated RE neuron firing. In contrast, the low-threshold spike of the RE neuron remained relatively unchanged by the increase of gTs. This suggests that the enhanced synchrony in the network was primarily due to a phase shift in the firing of the RE neurons with respect to the thalamocortical neurons. The ability of this phase-shift mechanism to lead to changes in synchrony was further examined using the model thalamic network. A similar increase in the period of RE neuron oscillations was obtained through an increase in the conductance of the calcium-mediated potassium channel. This change was once again found to increase synchronous firing in the network.

scholarly journals Altered resting-state functional connectivity of the frontal-striatal circuit in elderly with apathy

PLoS ONE ◽  
2021 ◽  
Vol 16 (12) ◽  
pp. e0261334
Author(s):  
Chizuko Hamada ◽  
Toshikazu Kawagoe ◽  
Masahiro Takamura ◽  
Atsushi Nagai ◽  
Shuhei Yamaguchi ◽  
...  
Keyword(s):  
Functional Connectivity ◽  
Resting State ◽  
Group Analysis ◽  
Underlying Mechanism ◽  
Brain Regions ◽  
Anterior Cingulate ◽  
Psychiatric Disease ◽  
Resting State Functional Connectivity ◽  
Dorsal Anterior Cingulate Cortex ◽  
Aged People

Apathy is defined as reduction of goal-directed behaviors and a common nuisance syndrome of neurodegenerative and psychiatric disease. The underlying mechanism of apathy implicates changes of the front-striatal circuit, but its precise alteration is unclear for apathy in healthy aged people. The aim of our study is to investigate how the frontal-striatal circuit is changed in elderly with apathy using resting-state functional MRI. Eighteen subjects with apathy (7 female, 63.7 ± 3.0 years) and eighteen subjects without apathy (10 female, 64.8 ± 3.0 years) who underwent neuropsychological assessment and MRI measurement were recruited. We compared functional connectivity with/within the striatum between the apathy and non-apathy groups. The seed-to-voxel group analysis for functional connectivity between the striatum and other brain regions showed that the connectivity was decreased between the ventral rostral putamen and the right dorsal anterior cingulate cortex/supplementary motor area in the apathy group compared to the non-apathy group while the connectivity was increased between the dorsal caudate and the left sensorimotor area. Moreover, the ROI-to-ROI analysis within the striatum indicated reduction of functional connectivity between the ventral regions and dorsal regions of the striatum in the apathy group. Our findings suggest that the changes in functional connectivity balance among different frontal-striatum circuits contribute to apathy in elderly.

scholarly journals Mechanisms of Human intelligence — From RNA and Synapse to Broadband

2019 ◽  
Author(s):  
Robert Traill
Keyword(s):  
Underlying Mechanism ◽  
Long Term Memory ◽  
Optical Signals ◽  
A Cell ◽  
Impossible Task ◽  
The Many ◽  
The Right ◽  
Label Sequence

Simple thought has been explained by the action-potential (AP) system with its synapses. In contrast, in-depth details for “Declarative” intellectual thought have been a complete mystery because (it is argued here) its main underlying mechanism is fundamentally different. Declarative thinking depends heavily on linear coding based on digit-like elements — something which an unaided AP system could never offer......Looking instead to psychology, Piaget (1920s) proposed basic units of action-sequences (“schèmes” whereby one could mentally construct object-concepts). There is now evidence that some ncRNA serves this verb-like action-coding role. — (Other ncRNA demonstrably serves as adjectival/adverbial “regulators” — while the remaining ≈3% of RNA encodes physical structures, the traditional noun-like role). If valid, then:–•NEW FOCUS ONTO ULTRAMICRO: — The whole Piagetian structure-coding for a concept could fit into one of the many 125nm capsids (“granules”). Moreover, many more concepts (and duplicates) could fit into a cell-body. — The vast abundance of coding-sites would allow comprehensive “wasteful” rapid use of Jerneian/Darwinian selection instead of problematic “writing down” of new learnings. — Estimates of memory-capacity increase vastly. — And hereditary-schèmes obviously explain inherited behaviour-traits. — Piaget’s other theory about develop¬mental stages also seems compatible.•Quantum-constraints ensure that such micro-sites would USE OPTICAL FREQUENCY signalling. That opens the way to greatly enhanced “Gigabit” rates, and optical-interference tricks.•MYELIN gets the EXTRA ROLE OF OPTIC-CABLE.So nerve-fibres become seen as simultan¬eous paths for two different types of signal (also demonstrated by Sun-et-al, 2010), with AP still dominant in some roles, but subservient to “UPE” optical signals elsewhere.•LOCATING MEMORIES? Choosing the right address means selecting some sort of “phone-number or numbered plug-socket.” That is best provided as an “address-label” sequence on the transmitted version of the schème-coding — in which case, actual destination-location may be less important.•“Moving-house” TO CORTICAL LONG-TERM MEMORY. The memory-move must preserve existing (i) memory-structure, and (ii) links to distant static archives. This “impossible” task would seem feasible if memories are actually held within individual cells (as above). There is indeed lifelong flow of such neurons in some mammals; but these flows seem to cease in adulthood for humans and dolphins! So the search continues.

scholarly journals A Pilot Study on Playback Theatre as a Therapeutic Aid after Natural Disasters: Brain Connectivity Mechanisms of Effects on Anxiety

2020 ◽  
Vol 4 ◽  
pp. 247054702096656
Author(s):  
Sarat Munjuluri ◽  
Peter K. Bolin ◽  
Y. T. Amy Lin ◽  
Nina L. Garcia ◽  
Leslie Gauna ◽  
...  
Keyword(s):  
Functional Connectivity ◽  
Natural Disasters ◽  
Resting State ◽  
Underlying Mechanism ◽  
Post Traumatic Stress ◽  
Resting State Functional Connectivity ◽  
Playback Theatre ◽  
Cohen’S D ◽  
Before And After ◽  
Cohen's D

Background Natural disasters can affect mental health and result in symptoms of depression, anxiety, and post-traumatic stress disorder (PTSD). Playback Theatre (PT) is a form of improvisation where actors play-back personal stories told by audience members. Whether PT can be therapeutic in post-disaster settings is not known. Method We used a series of PT performances and studied levels of depression, anxiety, and PTSD symptoms in a sample of 13 people affected by Hurricane Harvey that happened in Houston, TX, August 2017. Brain imaging, specifically resting state functional connectivity of the amygdala was also studied before and after the PT performances. Results Both anxiety ( p = .001, Cohen’s d = –1.25) and PTSD ( p = .002, Cohen’s d = –1.0) symptoms significantly decreased after a series of 4 PT performances from January 2019 – February 2019. Depression reduction was not significant. We performed resting state functional connectivity (RSFC) MRI before and after the series of performances. We used the right and left amygdala as seeds for RSFC analysis and found that the connectivity between the left amygdala and the bilateral supramarginal gyri was increased after PT. The bilateral supramarginal connectivity with the default mode and the saliency networks increased too, which correlated with reduction in anxiety scores. Conclusions PT may offer a form of intervention for anxiety caused by disasters. An increase in left amygdala/supramarginal gyri connectivity may be the underlying mechanism.

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