The Dynamic Brain in Action: Cortical Oscillations and Coordination Dynamics

Cortical oscillations are electrical activities with rhythmic and/or repetitive nature generated spontaneously and in response to stimuli. Study of cortical oscillations has become an area of converging interests since the last two decades and has deepened our understanding of its physiological basis across different behavioral states. Experimental and modeling work has taught us that there is a wide diversity of cellular and circuit mechanisms underlying the generation of cortical rhythms. A wildly diverse set of functions has pertained to synchronous oscillations but their significance in cognition should be better appraised in the more general framework of correlation between spike times of neurons. Oscillations are the core mechanism in adjusting neuronal interactions and shaping temporal coordination of neural activity. In the first part of this thesis, we review essential feature of cortical oscillations in membrane potentials and local field potentials recorded from turtle ex vivo preparation. Then we develop a simple computational model that reproduces the observed features. This modeling investigation suggests a plausible underlying mechanism for rhythmogenesis through cellular and circuit properties. The second part of the thesis is about temporal coordination dynamics quantified by signal and noise correlations. Here, again, we present a computational model to show how temporal coordination and synchronous oscillations can be sewn together. More importantly, what biophysical ingrediants are necessary for a network to reproduce the observed coordination dynamics

Characterization of the neocortical network excitability with multielectrode arrays: alterations in migraine and epilepsy mouse models.

missin

Cognitive and Perceptual Functions of the Visual Thalamus

The thalamus is classically viewed as passively relaying information to the cortex. However, there is growing evidence that the thalamus actively regulates information transmission to the cortex and between cortical areas using a variety of mechanisms, including the modulation of response magnitude, firing mode, and synchrony of neurons according to behavioral demands. We discuss how the visual thalamus contributes to attention, awareness, and visually guided actions, to present a general role for the thalamus in perception and cognition

Characterization of the neocortical network excitability with multielectrode arrays: alterations in migraine and epilepsy mouse models.

missin

Micro-, Meso- and Macro-Dynamics of the Brain

Neurosciences, Neurology, Psychiatr

Emergent Dynamics in Neocortical Microcircuits

Interactions among neurons can take place in a wide variety of forms. It is the goal of this thesis to investigate the properties and implications of a number of these interactions that we believe are relevant for information processing in the brain. Neuroscience has progressed considerably in identifying the diverse neuronal cell-types and providing detailed information about their individual morphological, genetic and electrophysiological properties. It remains a great challenge to identify how this diversity of cells interacts at the microcircuit level. This task is made more complex by the fact that the forms of interaction are not always obvious or simple to observe, even with advanced scientific equipment. In order to achieve a better understanding and envision possible implications of the concerted activity of multiple neurons, experiments and models must often be used jointly and iteratively. In this thesis I first present the development of a computer-assisted system for multi-electrode patch-clamp that enabled new kinds of experiments, allowing qualitatively different information to be obtained concerning the interaction of multiple neurons. In the following chapters I describe the different questions addressed and approaches utilized in the investigation of neuronal interactions using multi-electrode patch-clamp experiments. The principles behind the clustered organization of synaptic connectivity in Layer V of the somatosensory cortex are the first experimental finding presented. I then quantify the ephaptic coupling between neurons and how apparently minute signals might help correlate the activity of many neurons. Next, the ubiquity of a neocortical microcircuit responsible for frequency-dependent disynaptic inhibition is demonstrated and the summation properties of this microcircuit are then analyzed. Finally a model to explain the interactions between gap junctions and synaptic transmission in the olfactory bulb is proposed