Sufficient evidence has shown that synaptic reorganizations also occur in the immature brain, where a neuron may lose connections that it had initially established with other neurons, or receives increased connections with certain neurons multiply through certain stimuli.
As we discussed previously, the development of neural pathways is initially controlled by genetic mechanisms, but the neural circuits formed by these intrinsic mechanisms are only crudely laid out and contain myriad extremely redundant synapses. Scientific research has well established that the selective elimination of synapses depends on the sensory stimuli received by the brain. The brain eliminates neural connections that are seldom or ever used, in order to increase the accuracy and efficiency of the neural circuits. It is thus only through a baby’s sensorimotor experiences the initially formed circuitry is tested and refined. If a baby is deprived of the appropriate stimuli, for instance speaking, during the critical period, the corresponding neural circuits will not be able to form correctly, and it is difficult, if not impossible, to compensate for this lack later on.