Modelling Information Representation in the Brain Based on Coordination
Objective: Transient phase synchrony among neural populations is a subject of much active investigation in neuroscience where the key issue is how groups of oscillating neurons synchronize. What is the binding mechanism that allows groups of neurons to generate flexible representations of their environment and their actions in it? For dynamic coordination of neuron populations to take place the process must influence structural and synaptic plasticity across different regions of the brain. It is known that coordination between neurons takes place under the control of astrocytes where bi-directional signalling between astrocytes and neurons regulate higher cortical functions. Therefore, is it possible that astrocytes hold the key to explaining the binding mechanism? This project proposes to model the dynamic and coordinated interplay between distributed astrocyte and neuron populations. The ultimate goal of this research is to relate the manifestations of the model to cognitive and decision support functions.
Brief Description: Dynamic processes that humans take for granted such as making a decision or remembering, emerge from a pattern of interaction among widely distributed neural ensembles. A truly challenging problem is therefore to explain how these ensembles coordinate to give rise to thinking and coherent goal-directed behaviour via the binding of information. One clue to understanding this coordination phenomenon lies in the role of astrocytes. These glia cells possess neurotransmitter receptors and intracellular calcium mobilisers and can therefore integrate and modulate neuronal activity and synaptic transmission thereby influencing synaptic morphology and structural plasticity; effectively regulating the wiring and plasticity of the brain. Moreover, astrocytes greatly outnumber neurons by about 10:1 with over fifty percent of the axon spine interfaces in the hippocampus associated with astrocytes. Because individual astrocytes makes contact with many neurons and synapses, it is plausible that an individual release site of astrocyte associated neurotransmitter can lead to both local and long range changes (via gap junctions) in the astrocyte calcium level, providing a mechanism for dynamic coordination. Effectively this coordination of groups of neurons suggests that astrocytes play a key role in the learning and structural plasticity processes at different locations in the brain.
This research builds on current activities at the ISRC and on publications disseminated elsewhere. A model that relates the efficacy of a synapse to the astrocyte dynamics exists, where the dynamics of the astrocyte is controlled by the synapse. The model is based on experimental observations that support the hypothesis that standard synaptic transmission is influenced by calcium dependent astrocytic modulation, where the calcium level is affected by synaptic activity. Recent published work has also demonstrated that a learning strategy, based on neuron to neuron signalling, can reflect temporal patterns in the input data in the learned weights and subsequently assign the weight values to distal synapses. Essentially this work showed that a mechanism to facilitate “lateral data exchange” between neurons, gives a global controlling capability yielding the ability to assign the appropriate weight distribution across a network of synapses.
Outcome: This project will aim to model the coordination phenomenon between the astrocyte network and neuron populations. The model will explain the mechanism(s) that underpin coupling between these populations, which oscillate at different frequencies, and predict stable “inphase” and “antiphase” locking states that exist between these populations, and how external stimuli can effect time dependent state changes.
Personnel Involved
First Supervisor: McDaid, L Dr
Second Supervisor: Harkin, J Dr
Third Supervisor: Kelso, S Prof
Collaboration: This project does not involve collaboration with another establishment