Critical Periods in Brain Development

Sensitive “windows of opportunity” are periods in brain development when the brain needs certain input in order to develop specific skills through neural connections.

VISION – Two to four months. That’s why it’s essential to have infants’ vision problems (such as a wandering eye) corrected if needed. For example, newborns who are physically capable of seeing will become blind if their eyes are covered during the critical period for visual development (Greenough et al., 1989). 

LANGUAGE – Birth to age five. At first neonates can distinguish between all the sounds in human languages, including sounds that we can no longer hear since they are unused in English. When the baby becomes sensitized to the sounds of her own language, the unused connections are pruned (between six and twelve months). By one year of age, neurons needed for the native language are permanently in place. Fascinating recent research at the University of Washington found that babies who were exposed to foreign language sounds on a regular basis retained the ability to hear these sounds. The really fascinating part is that babies did not learn from videos or audio recordings. Only the infants who interacted with a live person could still hear the foreign language sounds at older ages (Kuhl, Tsao, & Liu, 2003).

MUSIC – Three to ten years is when a musical instrument can be learned most easily. Some studies have shown a connection between music and math abilities. John J. Medina, the author of Brain Rules for Babies (2011), recommends giving children music lessons since long-term, consistent exposure has been found to help children perceive others’ emotions and make friends.

EMOTIONAL — Birth to 18 months. This is one of the first of the brain’s circuits to develop, since social attachment and emotional regulation begin at birth. The first emotions are simple distress and contentment, which rapidly develop into more complex and varied emotions. When an infant feels safe and cared for, she or he can focus on exploration rather than on getting his or her needs met. This leads to a healthy attachment.

MATH AND LOGIC – One to four years. The understanding of numeric and analytical concepts develops during the preschool years when children are in stimulating environments. If they are not given these opportunities, children may struggle in this area in the future.

Important Brain Development Terms

• Neuron – nerve cell that make up the brain and nervous system
• Neurotransmitters – chemical impulses moving from one to neuron to another
• Synapse – where neurons meet (axons & dendrites connect through neurotransmitters)
• Pruning – how unused synapses disappear (“use it or lose it” principle) Blooming refers to the opposite, when the brain makes more dendrites & connections.
• Brain plasticity – The amazing ability of a developing brain to reorganize itself. The cerebral cortex (or higher brain) can adapt another section to take over the functions of a damaged section. This ability diminishes with age, although research has shown that even the brains of older adults can reorganize to some extent and produce a few new neurons after damage (Kolb & Gibb, 1999).
• Lateralization – How the two sides, or hemispheres, of the brain specialize to have different functions. This division of tasks begins at birth but is also determined by early experiences, as all of brain development seems to be.

• The left hemisphere specializes in analytical thought, logic, and reasoning, and controls the right side of the body. This is the dominant side in right-handed people. 
• The right hemisphere controls feelings, intuition, and imagination, as well as the left side of the body. Left-handed people are dominated by this side.
• Experience-expectant or Experience-dependent – the two ways the brain shapes itself. The first type, experience-expectant, is based on our brains expecting certain experiences at certain times (and leads to neuron pruning). The second type, experience-dependent, results from specific experiences and happens throughout our lives. This enables our brains to make new connections in response to repeated stimulation or practice (blooming). 
• Myelination – the process of building a fatty coating around the neurons that occurs from the bottom up (Deoni et al., 2011). This myelin sheath enables the brain to send messages more effectively and efficiently.
• Toxic Stress can occur when children experience long-lasting, frequent, and strong adversity (such as abuse or neglect) without the protective buffer of adult support. This results in a prolonged activation of physical stress response, which can disrupt the development of brain architecture as well as increase risks for lifelong disease and impairment. Some positive stress is a normal and needed part of development, and even a crisis may be tolerable if stress response is limited and is buffered by relationships with adults.