During development, 50% of neurons die; those that survive are those that

Around 50% of neurons die because they have not receive life-sustaining signal from the postsynaptic cell that is crucial to survive. These neurons die by apoptosis where biochemical events lead to cell changes and programmed cell death. Those neurons that survive during development find appropriate synaptic connections with other postsynaptic cells and those neurons were produce by ventricular zone of the brain who is capable of providing surplus of neurons.