Lorentz Center - Brain Waves from 22 Jun 2009 through 26 Jun 2009
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    Brain Waves
    from 22 Jun 2009 through 26 Jun 2009

 
Abstracts workshop Brain Waves:

Abstracts workshop Brain Waves:

 

Christoph Börgers

Title:

The response of classical Hodgkin-Huxley neurons to inhibitory pulses

 

Abstract:

Two fundamental mechanisms for generating gamma oscillations ("PING" and "ING") are based on the synchronization of populations of neurons by a single common inhibitory input pulse. The cause for this synchronization is an "attracting river" created by the inhibitory pulse. Trajectories synchronize by flowing into this river. I will briefly review how this works for theta neurons, then show that it does not work nearly as robustly for classical Hodgkin-Huxley neurons, and explain what goes wrong in that case. In general, synchronization of a population of neurons by an inhibitory pulse is quite robust when the neurons are of type I, but much less so when they are of type II.

 

There is some evidence that the phase response of principal cells in the cortex may often be of type II in the presence of depolarization-induced slow hyperpolarizing currents such as the M-current, but of type I in the absence of such currents. This suggests the possibility that cholinergic modulation, which down-regulates the M-current, may facilitate robust PING rhythms by causing a transition from type II to type I in the principal cells.

 

ING rhythms are generated by networks of fast-spiking interneurons alone, without participation of principal cells. In model networks of fast-spiking interneurons of type I, ING is known to break down easily in the presence of heterogeneity in the network, but can be stabilized by dendro-dendritic gap junctions. There is, however, some evidence that fast-spiking interneurons in the cortex may be of type II. Thus our results give a new reason to question the robustness of the ING mechanism in the cortex.

 

 

Lo Bour

Title:

Oscillatory neuronal activity in the human basal ganglia

 

Abstract:

During deep brain surgery (DBS) in patients with Parkinson’s disease, dystonia, and patients with related movement disorders, electrical activity of the neural structures is measured to refine the target position of the implantable electrical stimulator. These micro-electrode recordings (MER) normally include multi-unit activity derived from a very small tungsten micro-electrode tip. Also local field potentials (LFP) can be recorded in the basal ganglia. These LFPs are a superposition of all active electrical elements close to the recording electrodes, and can be considered as a intracerebral EEG.

It has been demonstrated that both MER and LFP show oscillatory activity that has a relationship with clinical symptoms of the movement disorders and the oscillatory activity also covaries with pharmacological therapy or DBS.

Several examples will be given of oscillatory behavior in the basal ganglia of the human brain and how this is related to normal and pathological functioning. Also the spatial distribution of spectral power across time time-locked to specific motor-tasks in patients with movement disorders and reward-tasks in patient with obsessive compulsive disorders will be discussed.   

 

Steve Coombes

Title:

Waves in neural field models

 

Abstract:

In this talk I will explore the way in which synaptically coupled neural networks may generate and maintain travelling waves of activity in rate based continuum models.  Although these models are non-local progress in recent years means that we are now in a position to address fundamental questions about the effects of intrinsic ionic currents, synaptic processing, and anatomical connectivity on travelling waves in neural tissue.  I will present a number of examples from both one and two dimensions, focusing on the contributions of axonal delays, adaptation, and slow T-type calcium currents to brain waves.

 

 

Andreas Daffertshofer

Title:

Phase dynamics in neural populations under impact of statistical feedback

 

Abstract:

T.b.c.

 

 

Wim van Drongelen, Hyong Lee, Sid Visser, Marc Benayoun, Edward Wallace,

Jack Cowan and Mark Hereld

Title:

Approaches for modeling brain waves in epilepsy

 

Abstract:

Epilepsy is a heterogeneous disease characterized by recurrent seizures and affecting 1-2% of the world population. The mechanisms causing seizure activity are commonly associated with hyperexcitability of neuronal networks, but the details are not well understood. This poor understanding is a principal reason for the limited success of antiepileptic drugs (AEDs): about ⅓ of patients are intractable and the AEDs have severe side effects. In spite of the development of new AEDs during the past decades, side effects are still problematic and the fraction of intractable patients has not been reduced. Therefore, the current strategy used to design anticonvulsant therapy needs critical review and the only hope for improvement seems to be a better fundamental understanding of the variety of mechanisms leading to epileptiform activity.

We propose to examine mechanisms of seizure generation with mathematical and computational modeling techniques, examples of which will be presented in the talk. Hereby some of the following will be considered. Although it is clear that multiple physio-pathological mechanisms underlie different types of epilepsy, common characteristics of different seizure types indicate that there may be a few fundamental principles at work and that understanding these first may help fill in the details later. Models using this approach should be as simple as possible while they must be capable of explaining the existence of non-seizure and seizure states and the sudden transitions between them.

For more detailed models, computational modeling may provide a tool to find potential mechanisms for seizure activity. Often, such models are designed to capture as much biological detail as possible, and are therefore populated with a broad range of measured or estimated physiological data.  The behavior of the model is subsequently tuned and validated against recorded activity patterns under a variety of conditions. We advocate an approach in which a more streamlined model, whose details are selected based on perceived relevance to a particular problem, is built to replicate targeted behaviors, and then used to find parameter sets that can generate such behavior. In the context of epilepsy, one might target certain physiological parameters to explore which regimes are associated with seizure and non-seizure behavior, and thus garner insight into the mechanisms leading to seizure activity. An advantage of the proposed theoretical approach is that many hypotheses can be falsified relatively quickly and easily while the remaining ones can be used for further experimental and clinical examination.  We discuss our experience with this approach, as well as some of the technical difficulties inherent in constraining even relatively simple and targeted models.

 

 

Konstantinos Efstathiou

Title:

Unstable attractors in pulse coupled oscillator networks

 

Abstract:

We consider networks of pulse coupled oscillators with non-zero delay. The coupling between the oscillators is given by the Mirollo-Strogatz function. Such networks are used for modelling, for example, the activity in biological neuron networks or the synchronization processes in networks of interacting agents. Because of the non-zero delay the state space of such systems is infinite dimensional. We introduce a metric in the state space in order to study the question of existence of unstable attractors, i.e., of saddle periodic orbits whose stable set has non-empty interior. We prove that for any number of oscillators $n\ge3$ there is an open parameter region in which the system has unstable attractors. Moreover, in the case of $n=4$ oscillators we show that there exist unstable attractors with heteroclinic cycles between them. Finally, we show that the flow of the system is discontinuous and we propose a different model with continuous flow.

 

 

Chris Fall

Title:

Does intracellular signaling support persistent activity in cortical microcircuits?

 

Abstract:

T.b.c.

 

 

Barbara Haendel

Title:

Cross - frequency coupling of brain oscillations in the neocortex

 

Abstract:

Cortical activity such as recorded by EEG or MEG is characterized by ongoing rhythms that encompass a wide range of temporal and spatial scales. Recent studies have suggested oscillatory interactions with faster oscillations being locked to preferred phases of underlying slower waves. While such an interaction is well described with relation to memory and hippocampus, more and more experiments show such a cross - frequency coupling also in tasks not directly related to memory and in areas of the neocortex. A series of studies reported that in auditory, visual as well as tactile tasks the power of gamma frequency is modulated by the phase of slower oscillations of various frequencies [e.g. 1, 2, 3]. Such interaction is discussed to be able to shape and optimize the neuronal response to sensory input. One interesting question therefore is if there are perceptual consequences of inter-frequency coupling. In a recent study we could show that the strength of such a power modulation of occipital high-frequency oscillations (in the gamma range) by the phase of a low-frequency oscillation (in the delta band) reflects the success of visual discrimination [4]. This provides evidence for the concept that coupling of different cortical oscillators plays a constructive role in signal detection.

 

[1] Osipova, D., Hermes, D., Jensen, O., 2008. Gamma Power Is Phase-Locked to Posterior Alpha Activity. PLoS one 3(12),

[2] Canolty, R.T., Edwards, E., Dalal, S.S., Soltani, M., Nagarajan, S.S., Kirsch, H.E., 2006. High gamma power is phase- locked to theta oscillations in human neocortex. Science 313, 1626–1628.

[3] Bruns, A., Eckhorn, R., 2004. Task- related coupling from high- to low- frequency signals among visual cortical areas in human subdural recordings. Int. J. Psychophysiol. 51, 97–116.

[4] Händel, B., Haarmeier, T., 2009. Cross- frequency coupling of brain oscillations indicates the success in visual motion discrimination. Neuroimage. 45(3), 1040-1046.

 

 

Geertjan Huiskamp:

Title:

Spatio-temporal effects of source cancellation in EG/MEG

 

Abstract:

Brain electrical activity can be measured remotely by EEG and its magnetic counterpart MEG. That this is possible at all is because populations of neurons can show simultaneous post-synaptical activity and because such populations are often arranged in parallel structures

in the outer cortical layers. The resulting EEG or MEG can in many cases by modelled adequately by an equivalent current dipole. This has clinical relevance, since in the case of epilepsy EEG/MEG can be used to accurately localize abnormal cortical activity and thus

provide essential information in cases where epilepsy surgery is an option. However, it is clear from invasive recordings of such patients that the generators of epileptic activity  that is most apparent in the EEG/MEG cover an area that extends a patch of cortex for which

cortical layers can be assumed to be parallel. This means that area's of opposing orientation can cancel and that area's that extend from sulcus to gyrus are represented differently in EEG and MEG. This can result in specific sensitivity for certain cortical regions. If activity propagates in a wave-like fashion over such area's spatio-temporal effects may occur in the EEG and MEG that have an effect on the interpretation, and on the applicability of the

equivalent current dipole model.

 

 

Martin Krupa

Title:

A possible role of gamma oscillations in stimulus selection

 

Abstract:

Abstract: In this talk we will discuss models of neuronal information transfer in the form of two competing gamma-modulated inputs and an output consisting of a single neuron or a small neuronal network. We focus on sinusoidal inputs with frequencies in the gamma range and on

slowly oscillating input modulated by gamma oscillations. Our simulations indicate that the presence of sufficient leakiness in the target or sufficient inhibition in PING-like models allows for the input with the stronger gamma amplitude to entrain the target neuron and to suppress the other input.

 

 

Fernando Lopes da Silva

Title:

Computational neurophysiology of transitions between normal and epileptic brain states

 

Abstract:

T.b.c.

 

 

McIntyre

Title:

 

Abstract:

T.b.c.

 

 

Hil Meijer

Title:

A mathematical model for localization of successively presented stimuli

 

André Noest

Title:

Persistent topological defects in cortical gamma-oscillations?

 

Abstract:

The spatial correlation range of cortical gamma-oscillation phase is too short to support its originally proposed role (long-range feature- binding), which has indeed been refuted by independent experiments. Subsequently, other functionally important roles (e.g. attention) have been proposed, but without considering whether these would be more robust to the

Limited coherence. The crude answer is: It depends on which typical spacetime phase-patterns are the underlying source of the decorrelation measured sofar. Smooth patterns would be acceptable, but point- or line-defects would predict dramatic local failures of the proposed function. Precisely such long-lived defects are typically generated by all

Relevant models. Indeed, they stem directly from the very nature of spontaneous oscillations -- global phaseshift invariance. For example, the normal- form dynamics (complex Ginzburg-Landau), generically creates spiral (vortex) singularities, separated by `shock'-boundaries. Such patterns coarsen only slowly, if at all (e.g. local inhomogeneities can pin a pattern).

Adding more realistic perturburbation terms does not get rid of such persistent defects -- in fact, this even leads to additional types of vortices, with `string'-type singularities that connect conjugate pairs, or form closed loops. Even the seemingly trivialising invocation of an external `pacemaker' that sends a global synchronising signal actually leads to highly non-trivial vortex-and-string pattern evolution. Any of these patterns would severely disturb all proposed functions of gamma-oscillations.

 

 

Oleksandr Popovych

Title:

Tremor entrainment by patterned low-frequency stimulation

 

Abstract:

For the therapeutic effect of deep brain stimulation, the standard therapy for medically refractory movement disorders, a proper electrode placement is of crucial importance. High-frequency test stimulation for tremor suppression is a standard procedure for functional target localization during deep brain stimulation. This method does not work in cases where

tremor vanishes intraoperatively, for instance, due to general anaesthesia or due to an insertional effect. To overcome this difficulty, we developed a stimulation technique that effectively evokes tremor in a well-defined and quantifiable manner. For this, we used brief high-frequency pulse trains administered at pulse rates similar to neurons' preferred burst

frequency. We applied this patterned low-frequency stimulation (PLFS) to a patient with spinocerebellar ataxia type 2 (SCA2) with pronounced tremor that disappeared intraoperatively under general anaesthesia. We show that PLFS can evoke tremor, phase locked to the stimulus, which is also in accordance with our computational results. Furthermore, a weak PLFS may cause low-amplitude, but strongly phase-locked

tremor. PLFS test stimulation provided the only functional information about target localization. Optimal target point selection was confirmed by excellent post-operative tremor suppression.

 

 

Jon Rubin

Title:

CAN currents and bursting

 

Abstract:

T.b.c.

 

 

Steve Schiff

Title:

Ensemble Kalman filtering for observation and control of cortical wave dynamics

 

Abstract:

We have in recent years learned that many of the prominent temporal rhythmicities in the brain have a spatiotemporal structure. The functional implications of such brain wave behavior generally remains to be resolved. We have developed a number of strategies for observation and control of such waves using ensemble nonlinear Kalman filtering techniques. We will first demonstrate a strategy of using a reduced mean field observer network model of cortex to track noise-contaminated measurements of wave behavior, and construct a feedback strategy to modulate wave frequency. We then demonstrate that such methods can be used with fundamental biophysical ionic-based models of neuron excitability. Lastly, we take model inadequacy formally into account, using an optimized parameter model network to assimilate complex network data – the ‘consensus set’. Finally, we apply such consensus set methods to assimilate real data from cortical wave experiments.

 

 

Eric Shea Brown

Title:

Stimulating layered neural networks -- optimization and entrainment

 

Abstract:

T.b.c.

 

 

Anton Sirota

 

Title:

Diversity and theta phase coordination of gamma oscillators in cortico-hippocampal system

 

Abstract:

Theta and gamma oscillations are believed to play an important role in the cortical network dynamics. Specifically, theta oscillation coordinates the dynamics across different brain regions, whereas gamma oscillations reflect synchronization within these local networks. Despite ample research on theta and gamma oscillations, a thorough investigation of the diversity of gamma oscillations in neocortex or hippocampus and their dynamics within theta oscillation is missing. We addressed this question by recording LFP and multiple single units in different layers in neocortex, entorhinal cortex and hippocampus, using extracellular recordings with silicon probes in rats during exploratory behavior and REM sleep.

 

Using spectral and latent variable analyses of unit firing and LFP, we reveal multiple gamma oscillators dominant in different frequency bands and with different anatomical profiles. These gamma oscillators exhibited very different dynamics within hippocampal theta oscillation cycle, which matches the dynamics of unit firing. This comprehensive view on the interplay between local network dynamics and global theta oscillation gives rise to novel perspective on the role of theta and various gamma oscillations in cortico-hippocampal system for learning and memory function.

 

 

Kees Stam

Title:

Synchronization and topology of ‘brain waves’ in epilepsy

 

Abstract:

Normal brain function requires both local processing of information as well as efficient exchange of information between widely distributed specialized brain areas. A central question in neuroscience is how this information exchange takes place, and how it breaks down in various neuropsychiatric disorders. Interactions between distributed brain regions can be studied by computing statistical interdependencies between time series of neural activity recorded over these areas; this concept is known as ‘functional connectivity’. Synchronization of neural activity in different frequency bands turns out to be a major principle of information exchange. Large arrays of correlations between pair wise channels of EEG or MEG can be further analyzed by approaching them as complex networks, with each channel representing a network node, and each correlation between two nodes a network link. The theory of complex networks has made enormous progress since the discovery of small-world and scale-free networks as paradigm models of complex systems. Application of modern network analysis to neuroscience data has shown that healthy brains are likely to be small-world networks characterized by a combination of high clustering and short path lengths (Reijneveld et al., 2007). This is evident from the neuronal up to the macroscopic level, and is true for anatomical as well as neurophysiologial data. In patients with epilepsy interictal network structure may be abnormally random and may change towards a small-world structure during the seizure; this has now been demonstrated both in intracranial as well as scalp recordings. Synchronization and network studies may increase our understanding of the processes underlying seizure generation and spreading, and could lead to new ways to detect epileptogenic networks in the brain, which could be of considerable interest, for instance for epilepsy surgery.

 

References:

Reijneveld JC, Ponten SC, Berendse HW, Stam CJ. The application of graph theoretical analysis to complex networks in the brain. Clin Neurophysiol. 2007; 118: 2317-2331.

 

 

David Terman, Andrew M. Oster, Balbir Thomas and Christopher P. Fall

Title:

The mitochondrial permeability transition pore confers excitability and CICR wave propagation

 

Abstract:

Accumulating evidence suggests that the mitochondrial network is an excitable medium which can demonstrate Ca2+ induced Ca2+ release via the mitochondrial permeability transition. The role of this excitability remains unclear, but mitochondrial Ca2+ handling appears to be a crucial element in diverse diseases such as diabetes, neurodegeneration, cardiac dysfunction and Parkinson’s disease. We have extended the modular Magnus-Keizer computational model for respiration-driven Ca2+ handling to include a transition pore and demonstrated both excitability and Ca2+ wave propagation that is accompanied by depolarizations similar to those reported in cell preparations. The waves depend on the energy state of the mitochondria, as well as other elements of the mitochondrial physiology. Our results support the concept that mitochondria can transmit state dependent signals about their function in a spatially extended way.

 

 

Paul Tiesinga

Title:

The role of neural waves in visual stimulus selection and attention: model studies at the local circuit level

 

Abstract:

When cued appropriately, our visual system effortlessly detects a target among many distracters. For example, consider the problem of finding a friend among a crowd of people at a train station. We do not yet understand at the neural level how stimulus selection happens, but experiments suggest that it must involve feature-selective neurons in the visual cortex, whose response is modulated by the task at hand. At the population level, it also requires a rerouting of information flow between different cortical areas, which is associated with coherence changes in various frequency bands.  A fundamental problem in neuroscience is to link response modulation at the single neuron level to that at the population level, which requires understanding the properties of the local cortical circuit and the development of new analysis methods. I will report on our recent efforts to make this link. We explore the hypothesis that interneuron diversity and interneuron-generated brain rhythms play a critical

role in selective attention. Because of advances in molecular biology, this hypothesis currently is the focus of a major experimental effort.

 

 

Magteld Zeitler

Title:

Effective communication between neuronal populations by neuronal oscillations

 

Abstract:

Since we are overwhelmed by sensory stimuli, our brain has to select relevant stimuli.  This is done by processing only the relevant information effectively and ignoring the other stimuli. For example, when you have an interesting discussion after dinner in a crowded restaurant, you will listen to and look at the speaker at your table, without being aware of the appearance of the guests at the other tables or their conversations. It is not clear how our brain can modulate the effectiveness of information processing. The Communication-Through-Coherence hypothesis by Pascal Fries states that the effectiveness of neuronal communication is determined by the relative phase of oscillatory activity of the sending and the receiving neuronal populations. We will explore this hypothesis in a cortico-spinal model. In agreement with recent experimental observations, we show that the information transfer from motor cortex to spinal cord is modulated by the phase of the beta-rhythm (15-25 Hz).



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