Hans Albert Braun

Hans Albert Braun
Philipps University of Marburg | PUM · Institut für Physiologie und Pathophysiologie

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169
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Publications

Publications (169)
Chapter
“We do not do what we want, we want what we do.” This is the logical consequence if one accepts that all our decisions are based on processes of our brain under deterministic natural laws. In recent years, this idea has received new nourishment through spectacular neurophysiological experiments demonstrating that the subjective experience of decisi...
Article
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If one accepts that decisions are made by the brain and that neuronal mechanisms obey deterministic physical laws, it is hard to deny what some brain researchers postulate, such as “We do not do what we want, but we want what we do” and “We should stop talking about freedom. Our actions are determined by physical laws.” This point of view has been...
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A transition between tonic and bursting neuronal behaviors is studied using a linear chain of three electrically coupled model neurons. Numerical simulations show that, depending on their individual dynamical states, the neurons first synchronize either in a tonic or in a bursting regime. Additionally, a characteristic firing rate, mediating tonic-...
Article
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Neuroscience is a multidisciplinary effort to understand the structures and functions of the brain and brain-mind relations. This effort results in an increasing amount of data, generated by sophisticated technologies. However, these data enhance our descriptive knowledge, rather than improve our understanding of brain functions. This is caused by...
Chapter
Neural activity at all functional levels is subjected to randomness and noise as can be seen in recordings of ion channels and action potentials as well as in physiological parameters of autonomic processes up to measures of mental and behavioral functions. This will be illustrated by experimental recordings supplemented by mathematical modeling st...
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Apart from the generally accepted concept of bottom-up causation there is increasing interest in elucidating particular phenomena suggesting top-down causation, especially in biology. It will be demonstrated, with examples from different levels of biological functions, that top-down causation cannot be a surprise as long as functional interrelation...
Conference Paper
The Virtual Physiology simulation software features classic physiological and pharmacological experiments with isolated preparations of the rat heart and vessels (SimHeart, SimVessel) and the frog muscle and nerve (SimMuscle, SimNerv), supplemented by technically more challenging experiments like voltage‐ and patch‐clamp recordings (SimNeuron), tha...
Article
The spiking activity of mammalian cold receptors is described by the Huber-Braun neuron model. Sweeping temperature as a control parameter across a biologically relevant range this model exhibits a complex bifurcation structure seen in the sequence of interspike intervals. The model’s distinctive feature is the interaction between a fast spike gene...
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A mechanism-based, Hodgkin-Huxley-type modeling approach is proposed that allows connecting the key parameters of experimental voltage-/patch-clamp data directly to the major control values of the model. The objective of this paper is to facilitate the use of mathematical modeling in supplement to electrophysiological recordings. Typical recordings...
Article
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The hypothalamic-pituitary-adrenal axis (also called the HPA or stress axis) exhibits distinct circadian and ultradian rhythms in cortisol release that cannot be explained solely by the feedback loops from cortisol to the control systems in the paraventricular nucleus (PVN) and pituitary gland. The HPA axis is intimately connected with other brain...
Article
Hemorrhagic insult is a major source of morbidity and mortality in both adults and newborn babies in the developed countries. The mechanisms underlying the non-traumatic rupture of cerebral vessels are not fully clear, but there is strong evidence that stress, which is associated with an increase in arterial blood pressure, plays a crucial role in...
Conference Paper
A FPGA hardware core has been designed for real-time network simulations with up to 400 physiologically realistic, conductance-based neurons of the Hodgkin-Huxley type. A PC-FPGA interface allows easy parameter adjustment and on-line display of basic synchronization measures like field potentials, spike times or color-coded voltages of the complete...
Data
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Some details on the numerical simulation. The supporting Information file Text S1 contains some more detailed information about: A: the definition of the wakefulness time intervals during the day and the night, and , respectively, used for evaluating the quality of the sleep-wake cycle; B: the extraction procedure of the diversified threshold poten...
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Recent advances in sleep neurobiology have allowed development of physiologically based mathematical models of sleep regulation that account for the neuronal dynamics responsible for the regulation of sleep-wake cycles and allow detailed examination of the underlying mechanisms. Neuronal systems in general, and those involved in sleep regulation in...
Article
In recent years biophysical approaches have had particular impact on the progress in physiological and biological research. In systems biology such progress is often associated with the terms "noise" and "chaos". The introduction of these physically based concepts into life sciences has essentially been promoted by the work of Frank Moss and his gr...
Article
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The dynamics of neurons is characterized by a variety of different spiking patterns in response to external stimuli. One of the most important transitions in neuronal response patterns is the transition from tonic firing to burst discharges, i.e., when the neuronal activity changes from single spikes to the grouping of spikes. An increased number o...
Article
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The response of a four-dimensional mammalian cold receptor model to different implementations of noise is studied across a wide temperature range. It is observed that for noisy activation kinetics, the parameter range decomposes into two regions in which the system reacts qualitatively completely different to small perturbations through noise, and...
Chapter
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Neurological and psychiatric disorders such as Parkinson’s disease and clinical depression are diseases of the nervous system. Disorders of different autonomic functions, including disturbances of sleep, energy balance, and hormonal secretion also have their origin in brain dysfunctions. However, while diseases associated with energy control or hor...
Chapter
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Thalamic activity significantly changes at the transitions form conscious wake to unconscious sleep states, going from an unsynchronized single-spike firing to synchronized discharges of impulse groups. These transitions can be simulated with a conductance-based model of neurons and synapses which assumes that alterations of thalamic synchronizatio...
Article
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Transitions from tonic firing (single spikes) to burst discharges (impulse groups) play an important role for neuronal information processing (sensory encoding, information binding) and are closely associated with neuronal synchronization in many physiological processes (hormone release, sleep-wake cycles) as well as in disease (Parkinson, epilepsy...
Chapter
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It is well established that noise, despite its mostly detrimental effects, can play a constructive role for information transfer. The best known example is stochastic resonance (SR) phenomena. SR means that there is an optimal level of noise for the detection of weak signals. In this study, a Hodgkin-Huxley type model neuron with subthreshold oscil...
Article
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We study the role of the strength of subthreshold currents in a four-dimensional Hodgkin-Huxley-type model of mammalian cold receptors. Since a total diminution of subthreshold activity corresponds to a decomposition of the model into a slow, subthreshold, and a fast, spiking subsystem, we first elucidate their respective dynamics separately and dr...
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We study a physiologically realistic implementation of internal stochasticity in a four-dimensional Hodgkin-Huxley type model of mammalian cold receptors. We show that in a deterministically tonic firing regime, this stochasticity can drive the neuron into a state of complex bursting behaviour. An explanation of the mechanism behind this effect is...
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We propose a mechanism-based modelling approach which brings together the most relevant features of neural dynamics and synaptic transmission for clinically valuable simulations of psychiatric disorders and their pharmaceutical treatment. It is based on a minimal, but physiologically justified concept, which allows to account for a great diversity...
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We introduce a physiology-based mathematical model of sleep-wake cycles, suggesting a novel mechanism of homeostatic regulation of sleep. In this model, the homeostatic process is determined by the neuropeptide hypocretin/ orexin, which is a cotransmitter of the lateral hypothalamus. Hypocretin/ orexin neurons are silent during sleep and active dur...
Article
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Alterations of individual neurons dynamics and associated changes of the activity pattern, especially the transition from tonic firing (single-spikes) to bursts discharges (impulse groups), play an important role for neuronal information processing and synchronization in many physiological processes (sensory encoding, information binding, hormone r...
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This special issue focuses on the most complex system we know: the brain. More precisely, it deals with the examination of the brain dynamics and disturbances which are clinically manifested in neurological and psychiatric disorders like epilepsy, Parkinson’s disease or mental depression. These diseases are often associated with disturbances of aut...
Article
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In healthy subjects, sleep has a typical structure of three to five cyclic transitions between different sleep states. In major depression, this regular pattern is often destroyed but can be reestablished during successful treatment. The differences between healthy and abnormal sleep are generally assessed in a time-consuming process, which consist...
Chapter
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Mental disorders are complex disturbances of the brain which lead to distinct emotional and cognitive alterations. These are manifested in an abnormal behavior of the patients as well as in biological markers such as nightly sleep interruptions and disturbed cortisol secretion, which suggests that the neuronal malfunctioning simultaneously affects...
Article
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We have examined the effects of current and conductance noise in a single-neuron model which can generate a variety of physiologically important impulse patterns. Current noise enters the membrane equation directly while conductance noise is propagated through the activation variables. Additive Gaussian white noise which is implemented as conductan...
Article
Neuronal synchronization plays a crucial role in many physiological functions such as information binding and wake-sleep transitions as well as in pathophysiological processes like Parkinson's disease and epileptic seizures. The occurrence of synchronized activity is often associated with significant alterations of the neuronal impulse pattern, mos...
Conference Paper
In recent years it was discovered that a neuropeptide orexin/hypocretin plays a main role in sleep processes. This peptide is produced by the neurons in the lateral hypothalamus, which project to almost all brain areas. We present a computational model of sleep-wake cycles, which is based on the Hodgkin-Huxley type neurons and considers reciprocal...
Article
The actions of intravenous anaesthetics on 5-HT(3AB) receptors have not been studied. Using oocyte electrophysiology, the effects of etomidate, propofol, and pentobarbital on human 5-HT(3A) and 5-HT(3AB) receptors were studied and compared. Inhibition of peak currents by all three compounds in both receptor subtypes was anaesthetic concentration-de...
Conference Paper
Disturbances of sleep are a prominent symptom of various disorders. Such disturbances are mostly analyzed on the level of sleep stages (hypnograms, see Fig.1 and Fig.2), which can be extracted from the EEG, EMG and EOG data. Sleep is subdivided to REM and non-REM sleep. REM-sleep is characterized by high frequency activity registered in EEG; rapid...
Article
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We studied the synchronous behavior of two electrically-coupled model neurons as a function of the coupling strength when the individual neurons are tuned to different activity patterns that ranged from tonic firing via chaotic activity to burst discharges. We observe asynchronous and various synchronous states such as out-of-phase, in-phase and al...
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The effects of bi-directional gap junction coupling of two model neurons with subthreshold oscillations have been examined when the individual neurons are operating at different dynamical states either in the tonic or bursting firing mode. Our simulations indicate that intermediate coupling strengths mostly lead to highly variable, often chaotic im...
Article
Biological systems are notoriously noisy. Noise, therefore, also plays an important role in many models of neural impulse generation. Noise is not only introduced for more realistic simulations but also to account for cooperative effects between noisy and nonlinear dynamics. Often, this is achieved by a simple noise term in the membrane equation (c...
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We survey possible applications of fast switching devices and induction rf at the Compact Linear Collider (CLIC). These applications include extraction kickers for the combiner rings, modulators for the drive-beam linac, fast intra-train feedback, induction crab cavities, halo kickers, emergency kickers, long-range beam-beam compensation, damping-r...
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We investigate the stimulus-dependent tuning properties of a noisy ionic conductance model for intrinsic subthreshold oscillations in membrane potential and associated spike generation. Upon depolarization by an applied current, the model exhibits subthreshold oscillatory activity with an occasional spike generation when oscillations reach the spik...
Article
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We discuss the possibility and importance of nuclear scattering processes inside a bunched hadron beam. Estimates are presented for the LHC.
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An efficient RF to beam energy transfer in the accelerating structures of the drive beam is one of the key points of the Compact Linear Collider (CLIC) RF power source. For this, the structures are fully beam-loaded, i.e. the accelerating gradient is nearly zero at the downstream end of each structure. In this way, about 96 % of the RF energy can b...
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The CLIC final focus system has been designed based on the local compensation scheme proposed by P. Raimondi and A. Seryi. However, there exist important chromatic aberrations that deteriorate the performance of the system. This paper studies the optimization of the final focus based on the computation of the higher orders of the map using MAD-X an...
Article
Many neurons of the peripheral and central nervous system exhibit oscillations in membrane potential that operate close to the spike threshold. Such neurons are e.g. found in the amygdala, the entorhinal cortex, in nociceptice dorsal root ganglion (DRG) cells and peripheral sensory receptors. In the latter, the oscillations are used for sensitive a...
Article
Robustness, i.e. the ability of a system to maintain stability despite perturbations, is an important issue considering normal function but also pathophysiological mechanisms. With respect to the latter, such robustness might even be a pitfall when it prevents the effects of treatments. In particular, this can be relevant in the case of sensitizati...
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The feasibility of a CLIC-LHC based FEL-nucleus collider is investigated. It is shown that the proposed scheme satisfies all requirements of an ideal photon source for the Nuclear Resonance Fluorescence method. The physics potential of the proposed collider is illustrated for a beam of Pb nuclei. Comment: Presented at PAC05, 16-20 May 2005, Knoxvil...
Article
Signal encoding in single neurons and neuronal nets can drastically change depending on their actual dynamical state. Dynamic state transitions are of particular relevance when different types of signals have to be simultaneously integrated because each signal can modify the transduction characteristics of each other signal due to the system's inhe...
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The CLIC test facility 3 (CTF3) provides a 3.5A, 1.6us electron beam pulse of 150MeV at the end of the linac. The average beam power is 4 kW. Beam losses will be monitored all along the linac in order to keep the radiation level as low as possible. The heavy beam loading of the linac can lead to time transients of beam position, size and energy alo...
Article
1.We recorded impulse activity of thermosensitive hypothalamic neurons in rat brain slices during superfusion with ethanol at constant temperatures and during slow sinusoidal temperature changes.2.At constant temperatures of 37°C, ethanol application typically induced a triphasic change of the firing rate: An initial excitation turned into complete...
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We explore the dynamics of a Hodgkin-Huxley-type model for thermally sensitive neurons that exhibit intrinsic oscillatory activity. The model is modified to include a feedback loop that is represented by two parameters: the synaptic strength and the transmission delay time. We analyze the dynamics of the neuron depending on the temperature, the syn...
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This paper studies the deterministic and stochastic dynamics of a thermo-receptor model. Special emphasis is paid to the transition zones between the main spiking patterns. In these zones, noise can induce or suppress spike generation, allowing for a nonmonotoneous dependence of the mean firing rate on the noise intensity. We show how this peculiar...
Article
Sensitization is a discussed as an important phenomenon underlying the initiation and progression of a variety of neuropsychiatric disorders as divers as epilepsia, substance-related disorders or recurrent affective disorders. The relevance to understand sensitization phenomena is emphasized by the recent finding that even single exposures to amphe...
Article
The Compact Linear Collider (CLIC) is a proposed design for a future e^+/e^- linear collider with a CM energy of 1-5 TeV and luminosity 10^33-10^34 cm-2s-1. The two beam acceleration method of CLIC will use a high intensity drive beam that produces RF power at 30 GHz to accelerate a main beam with a nominal gradient of 150 MV/m. To demonstrate the...
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Affective disorders tend to be recurrent and progressive and illness patterns typically evolve from isolated episodes at the beginning to more rapid, rhythmic and finally irregular "chaotic" mood patterns. Chararacteristic timecourse and disease patterns have prompted the consideration of nonlinear dynamics and chaos. In this paper we review some o...
Article
The dynamical features of spike train generation in the presence of noise are investigated for three difierent models of neural rhythm generators: a single neuron model that simulates impulse pattern modulation for temperature encoding in mammalian cold receptors, a minimal neural network that describes transitions between beta and gamma rhythms in...
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The performance of the LHC as a heavy-ion collider will be limited by a diverse range of phenomena that are often qualitatively different from those limiting the performance with protons. We summarise the latest understanding and results concerning the consequences of nuclear electromagnetic processes in lead ion collisions, the interactions of ion...