Physiological and pathological roles of astrocyte-mediated neuronal synchrony

Abstract

The function of the brain is fundamentally based on the processing of signals that are transferred from neuron to neuron at the chemical synapses. Neurons are indeed the only cells capable of generating an action potential that travels down the axon to trigger neurotransmitter release at the synapse and thus guarantees the activation of specific postsynaptic targets. The action potential carries information that is essentially encoded into distinct patterns of action potential firing. However, to be truly significant in information transfer and processing, action potentials need to be phase locked among distinct groups of neurons, i.e., neurons have to work synchronously. For instance, during the course of learning a motor task, single neuron activity in the rat sensory-motor cortex does not change significantly but the coordination of firings of individual cells from a distinct population of neurons increases with the prediction of the learned response (Laubach et al., 2000). The response from distinct neuronal populations of the visual cortex has been also observed to be synchronized on millisecond timescale after activation with a specific visual stimulus, thereby suggesting that synchronization could serve to encode contextual information by defining relations between the features of visual objects (Singer and Gray, 1995; Singer, 1999). Furthermore, in the olfactory bulb precise temporal firing patterns in distinct neuronal populations have been shown to be associated with perception of different odours (Wehr and Laurent, 1996).