CNS*1999
The Annual Computational Neuroscience Meeting
July 18-22, 1999, Pittsburgh, Pennsylvania
CNS*1999 Workshops
Workshop Title: Mathematical Reduction of Complex Neural Models: Methods and Uses of Reduced Models.
Moderator: Boris Gutkin
Description:
With increasing computational power, models of single neurons have become progressively more complicated, reflecting the multiplicity of trans-membrane conductances and the spatial structure of the neuron. While informative about specific biophysical mechanisms such models are mathematically unwieldy and do not yield to much formal analysis, nor do they easily connect with the more abstract neural network models used to study behavior of cell circuits and assemblies.
In the past several years, a number of mathematical techniques have been developed that allow one to reduce the mathematical complexity of neural models. The resulting models go far beyond the classical Integrate-and-Fire neuron in their ability to reproduce physiological phenomena and are amenable to mathematical analysis. Furthermore, the formal mathematical method makes it clear what are the assumptions inherent in the reduction process, and what are the structural and dynamical requirements for the reduction to be applicable.
In this workshop we shall present a survey of modern reduction methods with some examples of how the reduced models can be used.
Some examples of methods include:
- separation of time scales methods
- the spike-response models
- reductions using normal forms to give canonical phase models
- reduction of weakly and slowly coupled spiking neurons to neural networks
Duration: One Day
Format: Informal tutorial/mini-symposium
Tentative presenters: G. Bard Ermentrout; Carson Chow, John Rinzel, Boris Gutkin, Eugene Izhikevich, Larry Abbott
Workshop Title: In vivo intracellular recording in vertebrates: How and why?
Moderator: Dieter Jaeger
Description:
In vivo intracellular recordings in vertebrates are rumoured to be a frustrating experience best left to others.
In anesthetized animals it may not be so bad, however, depending on brain structure and cell type.
This workshop will collect the experiences, tips, and frustrations that the participants have had with in vivo intracellular techniques.
In particular we will address the question of how brain pulsations can be reduced. Other factors that are important in getting stable recordings, such as electrode shape and manipulator stability, will be duly noted.
And if we can do such recordings, what should we be using them for? The organizer claims that good intracellular recordings from behaving animals are the holy grail of computational neuroscience.
Duration: One day
Format: formal discussion
Workshop Title: Computational Neuroanatomy
Moderator: Giorgio Ascoli
Description:
I would like to stimulate the conversation and the exchange of opinions on the following questions:
- Why are there so many different morphological classes of neurons in nervous systems? Why is there such a wide morphological variability even within given morphological classes? What is the influence of dendritic morphology on neuronal electrophysiology and synaptic integration, either qualitatively (e.g. spiking VS bursting) or quantitatively (e.g. spike frequency, inter-train interval, etc.)?
- How does all of the above affect network connectivity? How do dendritic and axonal growth interact with each others, and what role does this play on ensable activity and dynamics?
- How can we describe in a concise, effective, complete and yet intuitive way the "fundamental" parameters of neuronal morphology and network anatomy? At what level a biologically plausible network model should include the mutual interplay between neuroanatomy and neurophysiology?
- In principle, what is the right approach to generate "virtual brains" in a computer? By assembling large-scale experimental databases? By generating accurate stochastic models constrained by experimental statistics? Or maybe an hybrid of these two approaches?
Duration: One day (Thursday)
Format: formal discussion
Workshop Title: Cortical Dynamics: Its Turtles From Here On Down
Moderator: Phil Ulinski
Description:
The nervous system of freshwater turtles makes an excellent preparation for neurobiological studies because these animals have a remarkable tolerance to anoxia. Turtle forebrains can, therefore, be maintained intact in an in vitro preparation and used in a variety of different kinds of studies. The goal for this minisymposium is to review recent work on the spatial and temporal dynamics of turtle visual cortex using an in vitro preparation of the turtle geniculocortical pathway. Philip Ulinski will discuss the use of turtle cortex for studies that relie upon intracellular recording techniques to test the key features of the canonical microcircuit concept formulated by Douglas, Martin and colleagues. David Senseman will discuss the use of turtle cortex for studies that use voltage sensitive dyes to characterize the spatiotemporal dynamics produced in the cortex by visual stimuli. Kay Robbins will discuss the use of dynamical systems methods to characterize the waves of activity produced in the cortex by visual stimuli. Bijoy Ghosh will describe a network model of turtle cortex, based on biophysically realistic models of individual neurons, which analyzes basic features of the waves of activity seen in voltage sensitive dye studies.
Duration: one day
Format: informal minisymposium.
Tentative Presenters: Phil Ulinski, David Senseman, Kay Robbins, Bijoy Ghosh
Workshop Title: Map development in visual cortex
Moderator: Geoff Goodhill
Description:
Models for the development of maps in visual cortex have a long history. From a relatively small set of basic mathematical principles, an impressive amount of experimental data can be accounted for. However, experimental advances continually provide new challenges, and theoretical advances pose new and often surprising predictions. The goal of the workshop is to review the different theoretical approaches in this fast-moving field, see where they agree and where they disagree in their biological predictions, and to gain further understanding of the strengths and weaknesses of different models.
Duration: One Day (Wednesday)
Format: Informatl Mini-symposium
Tentative Speakers:
Workshop Title: Nonlinear dynamics and noise in single neurons and in human psychophysics experiments.
Moderators: Hans Braun, Frank Moss
Description:
Neurons with subthreshold, noise mediated oscillators in reality and in a Hodgkin-Huxley model will be discussed. The temperature dependence, electrosensitivity and pharmacological modulation, bifurcations and the signatures of noise mediated low dimensional dynamical behavior in electro-, photo-, cold-receptors and hypothalamic neurons of example real neurons are discussed. Topology of the dynamics in the zero noise Hodgkin-Huxley oscillating neuron model is examined. An explosion of time intervals that results from the collision of a fixed point with a homoclinic orbit, is observed at low temperatures in real pacemaker neurons and in the HH model. By numerical simulation of a Hodgkin-Huxley model with an intrinsic oscillator, we compare the dynamics of the spike trains with the trajectories of the system. Reconstructed dynamics on the Poincare section and measures are discussed.
How computational neuroscience work led to animal studies that led to psychophysical studies that have now led to clinical studies. We demonstrate stochastic resonance-type behavior in: model neurons, rat cutaneous sensory neurons, and the human touch-sensation system. We discuss how, from a bioengineering and clinical standpoint, these developments may be particularly relevant for individuals with elevated sensory thresholds, such as older adults and patients with peripheral neuropathy.
The electroreceptor in the paddlefish (Polyodon Spathula) contains a quite rigid internal oscillator. Though their frequencies do not respond sensitively to external fields we have found that they can easily be synchronized (phase locked). The effects can be accurately mimicked with a noisy Hodgkin-Huxley or circle map.
Questions to be addressed:
- Do nonlinear dynamical processes play a role in encoding, or do they just simply reflect the stochastic nonlinear properties of these neurons?
- What is the source of "bursting" in the oscillating HH model, and could it be an explanation for bursting in pacemaker-type neurons?
- Does the explosion of time intervals encode temperature information?
- Is the spike timing sufficient to describe the underlying dynamics of the nervous system and what does the dynamics represent?
- Will noise enhanced sensory perception lead to new therapies for diseases of the nervous system?
- Does the rigidity of the oscillator and the ease of phase synchronization mean that the paddlefish uses a synchronization code to locate, track and find its planktonic prey?
Duration: Two days
Format: Informal Tutorial/Mini Symposium
Presenters:
- Hans A. Braun and Frank Moss. "Introduction and overview".
- Robert Gilmore (Drexel University, Philadelphia) "Topological analysis of chaos in neural spike train bursts"
- Alexander Neiman, Xing Pei (St. Louis) and Ulrike Feudel (Physics, University of Potsdam, Germany) "Homoclinic bifurcations and the explosion of time intervals in a Hodgkin-Huxley model and in Crayfish Caudal Photoreceptor neurons".
- Xing Pei (St. Louis) "Reconstruction of low dimensional dynamical properties from spike trains"
- J. J. Collins (Center for Biodynamics, Boston University) "Noise-enhanced sensory dynamics".
- Alexander Neiman, Xing Pei, Frank Moss and Hans A. Braun "Stochastic synchronization of the paddlefish electroreceptors with external fields"
- 7. Martin Huber (Marburg) "Noise and bifurcations in psychiatric models and experiments"
Workshop Title: Modeling the hippocampus: Is this the right direction, time and place?
Moderators: Phil Best and Ali Minai
Description:
A number of models have been developed to account for neural processes underlying the characteristics of place cells in the hippocampus and head-direction cells in related structures. The workshop will provide an opportunity to discuss a variety of questions concerning the performance of these models in explaining experimental data, the problems inherent in hippocampal modeling, and possible future directions. Questions:
- What is the state of the art in hippocampal models, and what are the most important outstanding questions?
- How well do the existing models fit existing data?
- Are there any properties of place and head-direction cells that make modeling them particularly difficult?
- Do any of the models make unintuitive predictions that have yet to be tested?
- Are there empirical questions yet to be addressed that would distinguish between the models?
- What methods, technologies, and experimental paradigms are needed to address the most important open questions in the field?
Duration: One day
Format: informal workshop