Wednesday, September 20, 2017

Journal club: The cortex as a central pattern generator




NATURE REVIEWS NEUROSCIENCE 6(6) 2005

by Rafael Yuste, Jason N. MacLean, Jeffrey Smith and Anders Lansner


A vast number of neurons in the brain cortex together generates synchronized oscillatory activity. In this review paper, the authors discuss how the neocortex neural network shares basic designs with the central pattern generator circuits in the spinal cord and brain stem.

For rhythmogenesis in a neural network, it seems like the general rule that self-boosting excitation within a functional unit is more important than reciprocal inhibition.  In the neocortical circuit, a population of neurons forms an excitatory kernel by being interconnected through recurrent excitation. Such excitatory neuronal population is capable of producing synchronized oscillatory activity through their active membrane properties and short-term synaptic plasticity. This circuit architecture is similar to the CPGs in the spinal cord and brain stem of vertebrates. The inhibitory connections are necessary for the regulation of the rhythm and spatiotemporal pattern of the network output.

The extent of spatial distribution is one of the major differences between the cortical network and the CPG in the brain stem/spinal cord.  In the cortex, the recurrent excitatory network is widely spread out over the neocortex, whereas in those for locomotion and breathing have bilaterally-grouped functional units. The other difference is high plasticity in the cortical network in contrast to the hard-wired CPGs in the spinal cord and brain stem. The connectivity in the cortex develops through activity-dependent Hebbian plasticity. We can call the cortex network as a learning CPG that is based on Hebbian assemblies and is specialized for learning and storing or retrieving memories.  Because of these properties, the neocortex network is highly fluidic.


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