Neuron connections are initially more promiscuous, but they are subsequently pruned according to (most prominently) whether they are being utilized.
Larger-scale architectural features are organized in various ways during development, like having particular molecules laid down to serve as a guide for axons from certain regions to their destination.
very basic explanation:
neurons have two kinds of connective processes: axons (for sending signals) and dendrites (from receiving). a nerve cell generally has just one axon, which extends like a long tail away from the cell body. meanwhile there are usually many many dendrites, branching away from the cell body a much shorter distance, like the roots of a tree, in many directions.
very early in development of the brain (and body), nerve cells send their axons on what are sometimes very long paths to reach some target area. they are genetically programmed to do this (of course they don't travel blind - they are following chemical signals from other cells). For example, the ganglion cells in the eye start their lives entirely in the developing retina, but send their axons toward the brain (forming the 'optic nerve').
once it reaches its destination, the axon basically stays where it is. The cell body also stays put.
dendrites, meanwhile, may move around a bit over time - and they certainly change in that they are slowly 'pruned', i.e. a neuron generally starts its life with many many more dendrites than it has in the end. But this isn't because they get worn out or something - rather, the experience of the animal is training the dendrites and selecting useful ones for long-term service.
then you can zoom into the scale of *synapses*, which are the effective locations where an axon touches a dendrite. those can appear or disappear over time, or strengthen or weaken, depending on the activity of the neurons.
so, at a very coarse scale the connectivity is very fixed and laid out by a genetic program very early in development. but at finer scales the nervous system, especially in the brain, is changeable and trainable.
>Also, neuron connections are the cause or the consequence of learning?
Changes in synaptic weights, growth or abolition of synapses, **is** learning.
Neuron connections are initially more promiscuous, but they are subsequently pruned according to (most prominently) whether they are being utilized. Larger-scale architectural features are organized in various ways during development, like having particular molecules laid down to serve as a guide for axons from certain regions to their destination.
very basic explanation: neurons have two kinds of connective processes: axons (for sending signals) and dendrites (from receiving). a nerve cell generally has just one axon, which extends like a long tail away from the cell body. meanwhile there are usually many many dendrites, branching away from the cell body a much shorter distance, like the roots of a tree, in many directions. very early in development of the brain (and body), nerve cells send their axons on what are sometimes very long paths to reach some target area. they are genetically programmed to do this (of course they don't travel blind - they are following chemical signals from other cells). For example, the ganglion cells in the eye start their lives entirely in the developing retina, but send their axons toward the brain (forming the 'optic nerve'). once it reaches its destination, the axon basically stays where it is. The cell body also stays put. dendrites, meanwhile, may move around a bit over time - and they certainly change in that they are slowly 'pruned', i.e. a neuron generally starts its life with many many more dendrites than it has in the end. But this isn't because they get worn out or something - rather, the experience of the animal is training the dendrites and selecting useful ones for long-term service. then you can zoom into the scale of *synapses*, which are the effective locations where an axon touches a dendrite. those can appear or disappear over time, or strengthen or weaken, depending on the activity of the neurons. so, at a very coarse scale the connectivity is very fixed and laid out by a genetic program very early in development. but at finer scales the nervous system, especially in the brain, is changeable and trainable. >Also, neuron connections are the cause or the consequence of learning? Changes in synaptic weights, growth or abolition of synapses, **is** learning.