Windows of opportunity or critical stages of brain development was first discovered by Hubel and Wiesel in the 1970's. They conducted an experiment preventing newborn kittens from using one eye for two weeks. After this period they discovered that although the eyes were perfect, they could not see.
They discovered that a baby's brain is born ready to send out signals to other parts of the body to form connections. If the connections are not formed during the critical window, the potential to connect becomes absent. Hence, the kittens had no visual stimulation to activate the cells, so they died or were diverted for another function. The potential to develop vision was gone forever.
Since Hubel's and Weisels' research in the 1970's other researchers have made significant advances regarding exactly how theses "windows of opportunity" or "critical stages of brain development" operate.
Research reveals that special genes called regulatory genes are what drive the opening and closing of windows of opportunity. Special regulatory genes are pre-programmed to tell other genes when to turn on and off. When regulatory genes turn on specific genes in brain areas that deal with traits such as vision, hearing, language, movement, music, social interaction, and emotions, it allows for phenomenally rapid learning in these brain areas. When regulatory genes tell certain genes to turn off, the opportunity for accelerated learning ceases.
Whilst the regulatory genes are opening and closing the windows of opportunity, the activity of neurotransmitters that support learning, such as dopamine and glutamate, are prompted to dramatically increase their activity. This timed increase in the activity of these learning neurochemicals facilitates the massive neural firing between cells and the blowing out of magnesium plugs from NMDA receptors, which is instrumental in the process of creating long-term memory. When the windows of opportunity are open, the increase in the neural activity allows us to learn at a rate much faster then we will ever be able to once the window shuts.