scholarly journals Complexity Collapse, Fluctuating Synchrony, and Transient Chaos in Neural Networks With Delay Clusters

2021 ◽  
Vol 15 ◽  
Author(s):  
S. Kamyar Tavakoli ◽  
André Longtin
Keyword(s):  
Firing Rate ◽  
Initial Conditions ◽  
Chaotic Regime ◽  
Local Network ◽  
Conduction Delay ◽  
Transient Chaos ◽  
Inhibitory Feedback ◽  
The Mean ◽  
Delay Differential ◽  
Local Circuitry

Neural circuits operate with delays over a range of time scales, from a few milliseconds in recurrent local circuitry to tens of milliseconds or more for communication between populations. Modeling usually incorporates single fixed delays, meant to represent the mean conduction delay between neurons making up the circuit. We explore conditions under which the inclusion of more delays in a high-dimensional chaotic neural network leads to a reduction in dynamical complexity, a phenomenon recently described as multi-delay complexity collapse (CC) in delay-differential equations with one to three variables. We consider a recurrent local network of 80% excitatory and 20% inhibitory rate model neurons with 10% connection probability. An increase in the width of the distribution of local delays, even to unrealistically large values, does not cause CC, nor does adding more local delays. Interestingly, multiple small local delays can cause CC provided there is a moderate global delayed inhibitory feedback and random initial conditions. CC then occurs through the settling of transient chaos onto a limit cycle. In this regime, there is a form of noise-induced order in which the mean activity variance decreases as the noise increases and disrupts the synchrony. Another novel form of CC is seen where global delayed feedback causes “dropouts,” i.e., epochs of low firing rate network synchrony. Their alternation with epochs of higher firing rate asynchrony closely follows Poisson statistics. Such dropouts are promoted by larger global feedback strength and delay. Finally, periodic driving of the chaotic regime with global feedback can cause CC; the extinction of chaos can outlast the forcing, sometimes permanently. Our results suggest a wealth of phenomena that remain to be discovered in networks with clusters of delays.

Effects of melanin-concentrating hormone on licking microstructure and brief-access taste responses

2006 ◽  
Vol 291 (5) ◽  
pp. R1265-R1274 ◽  
Author(s):  
John-Paul Baird ◽  
Catalina Rios ◽  
Nora Elizabeth Gray ◽  
Caroline Elizabeth Walsh ◽  
Shannon Glenora Fischer ◽  
...  
Keyword(s):  
Third Ventricle ◽  
Taste Stimulus ◽  
Water Solutions ◽  
The Third ◽  
Sucrose Solutions ◽  
Quinine Hydrochloride ◽  
Inhibitory Feedback ◽  
Melanin Concentrating Hormone ◽  
Taste Evaluation ◽  
The Mean

The effects of intracerebroventricular application of melanin-concentrating hormone (MCH) on licking for sucrose, quinine hydrochloride (QHCl), and water solutions were evaluated in two experiments. In experiment 1, rats received 90-min access to sucrose and water solutions after MCH or vehicle microinjection to the third ventricle (3V). MCH increased intake largely through increases in the rate of licking early in the meal and in the mean duration of lick bursts, suggesting an effect on gustatory evaluation. Therefore, in experiment 2, brief access tests were used with a series of sucrose and QHCl concentrations to behaviorally isolate the effects of intracerebroventricular MCH on gustatory evaluation. MCH uniformly increased licking for all sucrose solutions, water, and weak concentrations of QHCl; however, it had no effect on licking for the strongest concentrations of QHCl, which were generally avoided under control conditions. Thus MCH did not produce nonspecific increases in oromotor activity, nor did it change the perceived intensity of the tastants. We conclude that MCH enhanced the gain of responses to normally accepted stimuli at a phase of processing after initial gustatory detection and after the decision to accept or reject the taste stimulus. A comparison of 3V NPY and MCH effects on licking microstructure indicated that these two peptides increased intake via dichotomous behavioral processes; although NPY suppressed measures associated with inhibitory feedback from the gut, MCH appeared instead to enhance measures associated with hedonic taste evaluation.

scholarly journals A modified fluctuation test for elucidating drug resistance in microbial and cancer cells

2020 ◽  
Author(s):  
Pavol Bokes ◽  
Abhyudai Singh
Keyword(s):  
Drug Resistance ◽  
Cancer Cells ◽  
Colony Size ◽  
Random Number ◽  
Initial Conditions ◽  
Fano Factor ◽  
Persister Cells ◽  
Efficient Treatment ◽  
Fluctuation Test ◽  
The Mean

AbstractClonal populations of microbial and cancer cells are often driven into a drug-tolerant persister state in response to drug therapy, and these persisters can subsequently adapt to the new drug environment via genetic and epigenetic mechanisms. Estimating the frequency with which drug-tolerance states arise, and its transition to drug-resistance, is critical for designing efficient treatment schedules. Here we study a stochastic model of cell proliferation where drug-tolerant persister cells transform into a drug-resistant state with a certain adaptation rate, and the resistant cells can then proliferate in the presence of the drug. Assuming a random number of persisters to begin with, we derive an exact analytical expression for the statistical moments and the distribution of the total cell count (i.e., colony size) over time. Interestingly, for Poisson initial conditions the noise in the colony size (as quantified by the Fano factor) becomes independent of the initial condition and only depends on the adaptation rate. Thus, experimentally quantifying the fluctuations in the colony sizes provides an estimate of the adaptation rate, which then can be used to infer the starting persister numbers from the mean colony size. Overall, our analysis introduces a modification of the classical Luria–Delbrück experiment, also called the “Fluctuation Test”, providing a valuable tool to quantify the emergence of drug resistance in cell populations.

scholarly journals VoIP Speech Encryption System Using Stream Cipher with Chaotic Key Generator

2021 ◽  
pp. 240-248
Author(s):  
Mahmood Khalel Ibrahem ◽  
Hussein Ali Kassim
Keyword(s):  
Stream Cipher ◽  
Chaotic Maps ◽  
Initial Conditions ◽  
Local Network ◽  
Average Delay ◽  
Performance Quality ◽  
Chaotic Cryptography ◽  
Wireless Telecommunication ◽  
Encryption Decryption ◽  
Voice Data

Recently, with the development multimedia technologies and wireless telecommunication, Voice over Internet Protocol, becomes widely used in communication between connecting people, VoIP allows people that are connected to the local network or the Internet to make voice calls using digital connection instead of based on the analog traditional telephone network. The technologies of Internet doesn’t give any security mechanism and there is no way to guarntee that the voice streams will be transmitted over Internet or network have not been intercepted in between. In this paper, VoIP is developed using stream cipher algorithm and the chaotic cryptography for key generator. It is based on the chaotic maps for generating a one-time random key used to encrypt each voice data in the RTP packet. Chaotic maps have been used successfully for encryption bulky data such as voice, image, and video, chaotic cryptography has good properties such as long periodicity, pseudo-randomness, and sensitivity to initial conditions and change in system parameters. A VoIP system was successfully implemented based on the on ITU-T G.729 for voice codec, as a multimedia encoding of Real-time Transport Protocol payload data, then, apply a proposed method to generate three-mixed logistic chaotic maps [1] and then analysis the encryption/ decryption quality measures for speech signal based this method. The experimental work demonstrates that the proposed scheme can provide confidentiality to voice data with voice over IP performance quality, minimum lost in transmitted packet, minimum average delay, and minimum jitter.

scholarly journals Blink-Perturbed Saccades in Monkey. II. Superior Colliculus Activity

2000 ◽  
Vol 83 (6) ◽  
pp. 3430-3452 ◽  
Author(s):  
H.H.L.M. Goossens ◽  
A. J. Van Opstal
Keyword(s):  
Superior Colliculus ◽  
Firing Rate ◽  
High Frequency ◽  
Displacement Vector ◽  
Neural Mechanism ◽  
Fixed Number ◽  
Deep Layers ◽  
The Mean ◽  
Reflex Blinks ◽  
Frequency Burst

Trigeminal reflex blinks evoked near the onset of a saccade cause profound spatial-temporal perturbations of the saccade that are typically compensated in mid-flight. This paper investigates the influence of reflex blinks on the discharge properties of saccade-related burst neurons (SRBNs) in intermediate and deep layers of the monkey superior colliculus (SC). Twenty-nine SRBNs, recorded in three monkeys, were tested in the blink-perturbation paradigm. We report that the air puff stimuli, used to elicit blinks, resulted in a short-latency (∼10 ms) transient suppression of saccade-related SRBN activity. Shortly after this suppression (within 10–30 ms), all neurons resumed their activity, and their burst discharge then continued until the perturbed saccade ended near the extinguished target. This was found regardless whether the compensatory movement was into the cell's movement field or not. In the limited number of trials where no compensation occurred, the neurons typically stopped firing well before the end of the eye movement. Several aspects of the saccade-related activity could be further quantified for 25 SRBNs. It appeared that 1) the increase in duration of the high-frequency burst was well correlated with the (two- to threefold) increase in duration of the perturbed movement. 2) The number of spikes in the burst for control and perturbed saccades was quite similar. On average, the number of spikes increased only 14%, whereas the mean firing rate in the burst decreased by 52%. 3) An identical number of spikes were obtained between control and perturbed responses when burst and postsaccadic activity were both included in the spike count. 4) The decrease of the mean firing rate in the burst was well correlated with the decrease in the velocity of perturbed saccades. 5) Monotonic relations between instantaneous firing rate and dynamic motor error were obtained for control responses but not for perturbed responses. And 6) the high-frequency burst of SRBNs with short-lead and long-lead presaccadic activity (also referred to as burst and buildup neurons, respectively) showed very similar features. Our findings show that blinking interacts with the saccade premotor system already at the level of the SC. The data also indicate that a neural mechanism, rather than passive elastic restoring forces within the oculomotor plant, underlies the compensation for blink-related perturbations. We propose that these interactions occur downstream from the motor SC and that the latter may encode the desired displacement vector of the eyes by sending an approximately fixed number of spikes to the brainstem saccadic burst generator.

The Road to Chaos by Time-Asymmetric Hebbian Learning in Recurrent Neural Networks

2007 ◽  
Vol 19 (1) ◽  
pp. 80-110 ◽  
Author(s):  
Colin Molter ◽  
Utku Salihoglu ◽  
Hugues Bersini
Keyword(s):  
Supervised Learning ◽  
Hebbian Learning ◽  
Learning Algorithm ◽  
Initial Conditions ◽  
A Priori ◽  
Computational Cost ◽  
Chaotic Regime ◽  
Dynamical Regime ◽  
New Form ◽  
The Impact

This letter aims at studying the impact of iterative Hebbian learning algorithms on the recurrent neural network's underlying dynamics. First, an iterative supervised learning algorithm is discussed. An essential improvement of this algorithm consists of indexing the attractor information items by means of external stimuli rather than by using only initial conditions, as Hopfield originally proposed. Modifying the stimuli mainly results in a change of the entire internal dynamics, leading to an enlargement of the set of attractors and potential memory bags. The impact of the learning on the network's dynamics is the following: the more information to be stored as limit cycle attractors of the neural network, the more chaos prevails as the background dynamical regime of the network. In fact, the background chaos spreads widely and adopts a very unstructured shape similar to white noise. Next, we introduce a new form of supervised learning that is more plausible from a biological point of view: the network has to learn to react to an external stimulus by cycling through a sequence that is no longer specified a priori. Based on its spontaneous dynamics, the network decides “on its own” the dynamical patterns to be associated with the stimuli. Compared with classical supervised learning, huge enhancements in storing capacity and computational cost have been observed. Moreover, this new form of supervised learning, by being more “respectful” of the network intrinsic dynamics, maintains much more structure in the obtained chaos. It is still possible to observe the traces of the learned attractors in the chaotic regime. This complex but still very informative regime is referred to as “frustrated chaos.”

Sympathetic modulation of activity in rat dorsal root ganglion neurons changes over time following peripheral nerve injury

1996 ◽  
Vol 76 (2) ◽  
pp. 753-763 ◽  
Author(s):  
M. Michaelis ◽  
M. Devor ◽  
W. Janig
Keyword(s):  
Sciatic Nerve ◽  
Firing Rate ◽  
Nerve Injury ◽  
Dorsal Root ◽  
Sciatic Nerve Injury ◽  
Dorsal Root Ganglion Neurons ◽  
Nerve Lesion ◽  
Sympathetic Stimulation ◽  
The Mean ◽  
Ganglion Neurons

1. We recorded from centrally connected axons isolated from the proximal stump of the sciatic nerve in intact rats and in rats whose nerves had been transected 4 days-6 mo previously. Afferent axons selected for study had spontaneous impulse activity that originated ectopically in dorsal root ganglia (DRGs) L4 and L5. The sympathetic supply of these DRGs was excited by repetitive electrical stimulation of ventral roots T13 and L1. We examined quantitatively changes in afferent ongoing firing evoked by sympathetic stimulation. Results are based on observations from 161 neurons in rats with sciatic nerve injury and from 58 neurons in control rats with intact sciatic nerves. Of these 219 neurons, 204 had myelinated fibers (A neurons) and 15 had unmyelinated fibers (C neurons), on the basis of measurements of conduction velocity. 2. In rats with nerve injury the majority of the spontaneously active neurons tested (95 of 161) responded to sympathetic stimulation with a change in ongoing firing frequency: 41 neurons exhibited a significant increase in discharge frequency that was often followed by suppression (28 of 41), and 54 neurons responded with a decrease in ongoing activity (simple suppression). In control rats, in contrast, only 1 of the 58 spontaneously active sensory neurons tested responded to sympathetic stimulation. 3. In A neurons, the response pattern changed systematically with time after sciatic nerve injury. At 4-22 days after nerve lesion, excitation was much more common than suppression. At 60-93 days, excitation and suppression occurred about equally. At 110-171 days, suppression was by far the more common response. 4. Of the 14 C neurons, 2 were excited by sympathetic stimulation (at 4-22 days postoperative) and 10 were suppressed (2 at 4-22 days, 8 at > 60 days). The only spontaneously active C neuron found in control rats was not affected by sympathetic stimulation. 5. The magnitude of responses in the three postoperative intervals investigated was similar. This was so for both the excitatory and the simple suppressive responses. The average latency between onset of stimulation and excitatory responses in afferent A fibers (approximately 10 s) was significantly less than the latency to simple suppressive responses (approximately 20 s). 6. The mean spontaneous firing rate of A neurons decreased with time after nerve lesion. No change was observed in C neuron activity. The mean firing rate of A neurons was significantly higher than that of C neurons 4-93 days after nerve lesion, but not later. In all three postoperative periods investigated, the mean rate of spontaneous activity was the same in A neurons that responded to sympathetic stimulation and A neurons that did not. 7. The results show that nerve injury triggers sympathetic-sensory coupling within rat DRGs. Excitatory coupling is preferentially present in the period shortly after nerve injury, and is subsequently replaced by suppressive coupling. This suggests that there is a gradual change in the underlying coupling mechanism.

The Service Time Properties of an Unreliable Server Characterize the Exponential Distribution

1994 ◽  
Vol 26 (01) ◽  
pp. 172-182 ◽  
Author(s):  
Z. Khalil ◽  
B. Dimitrov
Keyword(s):  
Exponential Distribution ◽  
Service Time ◽  
Initial Conditions ◽  
Mean Values ◽  
Unreliable Server ◽  
Service Disciplines ◽  
The Mean ◽  
Server Reliability ◽  
Preemptive Repeat Different

Consider the total service time of a job on an unreliable server under preemptive-repeat-different and preemptive-resume service disciplines. With identical initial conditions, for both cases, we notice that the distributions of the total service time under these two disciplines coincide, when the original service time (without interruptions due to server failures) is exponential and independent of the server reliability. We show that this fact under varying server reliability is a characterization of the exponential distribution. Further we show, under the same initial conditions, that the coincidence of the mean values also leads to the same characterization.

scholarly journals Simple in situ decompression for idiopathic cubital tunnel syndrome using minimal skin incision

2010 ◽  
Vol 63 (9-10) ◽  
pp. 601-606 ◽  
Author(s):  
In-Ho Jeon ◽  
Ivan Micic ◽  
Byung-Woo Lee ◽  
Seong-Man Lee ◽  
Poong-Tak Kim ◽  
...  
Keyword(s):  
Postoperative Outcome ◽  
Skin Incision ◽  
Cubital Tunnel Syndrome ◽  
Cubital Tunnel ◽  
Invasive Technique ◽  
Conduction Delay ◽  
Surgical Trauma ◽  
Tunnel Syndrome ◽  
The Mean

Cubital tunnel syndrome is one of the most frequently occurring compression neuropathy in the upper limb next to carpal tunnel syndrome. Recent minimal invasive technique has prompted us to gain clinical experience with simple in situ decompression with minimal skin incision for idiopathic cubital tunnel syndrome. Sixty six consecutive patients with cubital tunnel syndrome were treated using minimal skin incision technique. The mean age of the patients was 49.7 (range: 15-77) years and average follow up period was 23.9 months (range: 12-60 months). The severity of ulnar neuropathy was classified according to the McGowan classification: there were 17 in grade I , 47 in grade II and 2 in grade III. A preoperative nerve conduction study was done by inching method, which revealed motor conduction delay around the medial epicondyle. All operations were carried out in a day surgery unit under local anesthetics. The postoperative outcome was evaluated by Messina classification. The mean duration of the operation was 12 minutes. The technique was highly satisfactorily esthetic for all. Over 80% of the patients were completely satisfied with the procedure taking into consideration their symptoms. Postoperative outcome measures and patient satisfactions (pain, return to normal activities and work, scar and pillar tenderness) were comparable with published series of anterior transposition. The overall satisfactory results were recorded 81% in the patients of McGowan stage I and II. There were 2 cases of hematoma as a postoperative complication. This procedure is comparably effective alternative which involves less surgical trauma, morbidity and rehabilitation time with good surgical outcomes especially in mild and moderate degrees. Minimal skin incision is a simple, safe and effective method to treat patients with idiopathic cubital tunnel syndrome.

Effect of an Azimuthal Mean Flow On the Structure and Stability of Thermoacoustic Modes in an Annular Combustor Model with Electroacoustic Feedback

2020 ◽  
Author(s):  
Sylvain C. Humbert ◽  
Jonas Moeck ◽  
Alessandro Orchini ◽  
Christian Oliver Paschereit
Keyword(s):  
Mach Number ◽  
Initial Conditions ◽  
Mean Flow ◽  
Final State ◽  
Mean Velocity ◽  
Acoustic Damping ◽  
Annular Combustor ◽  
The Mean ◽  
High Mach ◽  
The Stability

Abstract Thermoacoustic oscillations in axisymmetric annular combustors are generally coupled by degenerate azimuthal modes, which can be of standing or spinning nature. Symmetry breaking due to the presence of a mean azimuthal flow splits the degenerate thermoacoustic eigenvalues, resulting in pairs of counter-spinning modes with close but distinct frequencies and growth rates. In this study, experiments have been performed using an annular system where the thermoacoustic feedback due to the flames is mimicked by twelve identical electroacoustic feedback loops. The mean azimuthal flow is generated by fans. We investigate the standing/spinning nature of the oscillations as a function of the Mach number for two types of initial states, and how the stability of the system is affected by the mean azimuthal flow. It is found that spinning, standing or mixed modes can be encountered at very low Mach number, but increasing the mean velocity promotes one spinning direction. At sufficiently high Mach number, spinning modes are observed in the limit cycle oscillations. In some cases, the initial conditions have a significant impact on the final state of the system. It is found that the presence of a mean azimuthal flow increases the acoustic damping. This has a beneficial effect on stability: it often reduces the amplitude of the self-sustained oscillations, and can even suppress them in some cases. However, we observe that the suppression of a mode due to the mean flow may destabilize another one. We discuss our findings in relation with an existing low-order model.

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