Research

• development of methods to reconstruct Current Source Density reliably in different experimental settings from local field potentials
• analysis of local field potentials (LFP), in particular CSD reconstruction
• information processing in the cortico-thalamic part of the rat’s somatosensory system and the cat's visual system, modeling and analysis of local field potentials
• modeling thalamocortical loop,
• the role of extrageniculate visual pathway in movement perception, modeling and analysis of spiking activity, coding and variability in extrageniculate visual pathway
• analysis and modeling of data from behavioral mice experiments
• tools for 3-D brain atlases,
• development of databases to store digital representations of histology data and tools for creation of histology-based 3D brain atlases.
  

Our general aim is the development of analysis tools and models to understand the dynamics in neural tissue during processing of sensory information. We are particularly interested in functioning of early levels of sensory systems, in particular thalamo-cortical loops, but we also study the extrageniculate pathway of the visual system and behavior of mice in automatized IntelliCages. For other projects we run see

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or this movie of extracellular potential generated by the cortical column in a thalamo-cortical network.

Reconstruction of current source density in many dimensions for realistic geometries of recording setups

Electric potential measured extracellularly in the brain (Local Field Potential, LFP) carries informa­tion about activity of neural populations which can be remote from the place of recording. To find out the local cellular activity one must reconstruct the current source density (CSD) generating the measured field. We developed a method allowing precise reconstruction of CSD in three dimen­sions from a set of recordings obtained on a Cartesian grid (Łęski et al., 2007, Wójcik and Łęski, 2009). In col­laboration with Gaute Einevoll's group from Uni­versity of Life Sciences, Ås, Norway, we are currently de­veloping a similar method in 2D for analysis of recordings from electrode arrays. In the long term we would like to construct a general variant which would not require recording positions on a specific grid and would be able to deal with any realistic geometry of electrode contacts. We are developing an open toolbox implementing our methodolo­gy which will be distributed freely in the com­munity. Our 3D method is used for analysis of dynamics of thalam­ic acti­vation in stimulation of somato-senso­ry pathway in anes­thetized rat and ac­tivity in the barrel cortex in behaving rats. Both projects are in collaboration with Ewa Kublik and Andrzej Wróbel, IBD PAN. Two dimensional data to be analyzed come from the labo­ratory of John Gigg from Univer­sity of Manchester, UK, from experiments in the subiculum and were obtained with a multishaft electrode giving 8x8 simultaneous recordings on a grid of 200 μm interelectrode distance.

Collaboration: A. Wróbel, E. Kublik, IBD PAN, Warsaw, Poland; G. Einevoll, UMB, Ås, Norway; J. Gigg, UM, Manchester, UK.

Modeling thalamocortical loop

Our method of reconstruction of CSD from recordings on a finite grid makes certain assumptions which are difficult to establish experimentally but can be profitably investigated in realistic models. Models of different types provide also the best framework for testing various methods of data analysis, since every detail can be controlled there. We plan to develop several different models of the thalamocortical loop of rat somatosensory system. So far we have constructed a simple neural field model to test methods for measuring synchronization in this system (Łęski and Wójcik, 2008). We plan to develop a large-scale realistic model to model the LFP and CSD activity in the thalamus and cortex after stimulation of rat vibrissa. To do it we will use a methodology to automatically generate populations of realistic neuron models using L-systems – an approach from fractal geometry used to describe complex random morphologies in a synthetic way. This approach has been extensively explored in neuroscience by G. Ascoli at George Mason University. However, it has not been used for the evaluation of potentials generated by populations of such neurons. We should be able to combine fractal geometry (Wójcik, 2000) with biophysics to obtain reasonable estimates of fields generated in the tissue by populations of different cells and with network dynamics.

Collaboration: A. Wróbel, IBD PAN, Warsaw, Poland

Coding and variability in extrageniculate visual pathway

Coding and decoding of sensory information in the brain is one of the outstanding problems of neu­roscience. It is particularly striking given the variability of neural responses and the stability of our percepts. A natural approach to the problem of coding is through the theory of probability and infor­mation theory (Rieke et al., 1997). We are working to understand the coding properties and variabili­ty of responses of cells in superior colliculus, the major structure in the extrageniculate vi­sual pathway. We are building quantitative point process models to describe activity of every cell. We call it “spike kinematics” as it is separate from membrane mechanism (“spike dynam­ics”) but it puts constraints on possible models of spike generation. The long-term goal is to find realistic models of these cells based on available morphological and biophysical data satisfying the constraints.

A crucial component of neural codes is provided by correlations among different cells. To study such effects in the visual system we will analyze simultane­ous recordings from multiple cells in different structures of geniculate and extrageniculate visual pathways of the cat (data provided by W. Waleszczyk, IBD PAN). We plan development, ap­plication and testing of different synchroniza­tion and cooperation methods obtained within information theory and dynamical systems approach once the data become available.To test the viability of these methods we will also develop models of networks of spiking neurons with different topologies and check to which extent the considered methods are able to extract these topologies.

Collaboration: A. Wróbel, W. Waleszczyk IBD PAN, Warsaw, Poland