Morpholess Neurons Compromise the Development of Cortical Connectivity

Abstract

It is currently accepted that cortical maps are dynamic constructions that are altered in response to external input. Experience-dependent structural changes in cortical microcurcuts lead to changes of activity, i.e. to changes in information encoded. Specific patterns of external stimulation can lead to creation of new synaptic connections between neurons. The calcium influxes controlled by neuronal activity regulate the processes of neurotrophic factors released by neurons, growth cones movement and synapse differentiation in developing neural systems. We propose a model for description and investigation of the activity dependent development of neural networks. The dynamics of the network parameters (activity, diffusion of axon guidance chemicals, growth cone position) is described by a closed set of differential equations. The model presented here describes the development of neural networks under the assumption of activity dependent axon guidance molecules. Numerical simulation shows that morpholess neurons compromise the development of cortical connectivity. I. INTRODUCTIONNeural networks are not constant structures. Modification in neural nets leads to changes in mapping of input signal to output. The most explored type of neural plasticity is synaptic plasticity. Synaptic plasticity deals with modifications of connection strength between neurons. It is an activity dependent process, and synaptic efficacy modifications depend on activity of postsynaptic and presynaptic neurons [1,2]. The second type of plasticity is known as structural plasticity. Structural plasticity deals with anatomical structure of neurons, and connections between neurons. The anatomical structures of neurons are subject to variation, and new connections between neurons can be established or deleted [3] in the course of development of neuron net. Structural plasticity as well as synaptic plasticity is a permanent and activity dependent process. Because it is an activity dependent process it can be the basis of learning. Activity-dependent modifications of neural circuits lead to changes in activity pattern of whole network. The geometrical properties of neurons should be considered in the theoretical investigations of structural plasticity of neural netsworks. The network must be considered as a system of neurons in three dimensional neuropil where neurons communicate with each other. The geometrical properties of neurons and the neuropil where neurons are constituent elements of networks. The neural networks generate activity patterns which depend on the intrinsic state of individual neuron and external influences on the system. This activity influences structural plasticity process. An external signal changes the activity pattern and leads to creation of new connections i.e. network will be modified according to external information.The neurons without connections can be considered a system of neurons in three dimensional space. At the beginning, the neurons interact only by emission of chemicals. Even no connections between neuron...

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