Critical Period In Brain Development
Posted on September 21 2019
Find out what a critical period is in brain development and what parents should do to promote optimal brain growth in their children.
Table of Contents
What Is A Critical Period
A critical period is a phase during which a region of the brain is relatively more plastic and therefore more susceptible to the influence of experience in forming new synapses. Synaptic connections usually stabilize after this window of time and it becomes harder to create new connections.
In developmental psychology, during this critical period of development, a new skill or trait is usually formed given a specific experience is presented.
If the critical experience is not available during this period of time, it becomes much harder, less successful or even impossible to acquire the skill or trait after the window of opportunity closes.
Critical Period Example – Language Proficiency
One of the best examples to illustrate a critical period is learning the correct pronunciation and grammar in a new language.
A child can acquire a second language and attain proficiency much easier than adults can.
But once a child reaches puberty, they are more likely to have trouble with phonology or grammatical processing.
So the critical period for new language acquisition is believed to be before puberty1.
What Is A Sensitive Period
A sensitive period is similar to critical period in which a region of the brain is relatively more plastic and more sensitive to the influence of experience in forming new synapses. However, new synapses can still formed for an extended period of time outside of the optimal period although it’s more difficult. Some scientists refer to this as the weak critical period.
Sensitive Period Example – Language Acquisition
Although learning perfect phonology and grammar in a second language has a critical period, learning the usage of it seems to have more a sensitive period rather than a critical period.
So it is still possible for grownups to learn to use a new language beyond puberty, although it’s harder and may take longer compared to young children.
Why Is Critical Period Important
Critical periods are important because many crucial functions of our body are established during those periods, and some only during those periods.
Scientists have found that the following functions are best developed during critical periods:
The sensitive period of emotional regulation is believed to be from birth to age 2.
In a study in a Romanian orphanage, only orphans who were adopted by foster family before the age of 2 developed emotional regulation skills comparable to those of the never institutionalized children2.
There are different critical periods for different visual functions of the visual system. They usually fall between eye opening and puberty3.
For example, visual acuity usually develops from birth to around age 5 and the period between age 3 and 5 shows the most growth. Stereopsis, the perception of depth, has a critical period that ends at age 2.
Sensitivity to damage also has its own critical period in visual development. For instance, amblyopia, the condition where one of the eyes has reduced vision because the eye and brain are not working together properly, can result between several months old and 7 or 8 years old.
The critical period for new language acquisition is believed to be before puberty1.
After puberty, it is very hard, if not impossible, to attain proficiency in accent and grammar of the new language.
Absolute pitch in music listening
Absolute pitch is the ability to identify and produce the pitch of a musical sound without an external reference point4.
Children who started musical training between age 4 and 6 are most likely to reach absolute pitch and training that begins after the age of 9 rarely leads to that level of proficiency5.
For children who are born with congenital deafness, the absence of auditory input form birth can affect the normal growth of a functional auditory system, severely affecting their ability to learn oral language.
Scientists have found that when cochlear implants are installed to bypass the non-functional inner ears in these children before age 3.5, they can most likely learn to speak successfully, especially if they are also exposed to language-rich environments6.
Final Thoughts On Critical Periods
It may feel overwhelming that there are so many different critical periods in the brain development journey.
As parents, we should make sure our children are not deprived of critical experiences, especially during critical periods.
But some of the development are actually experience-expectant, meaning the stimuli required for development are practically guaranteed to be available in daily life, e.g. the capacity for language, vision and hearing. Parents rarely have to make an effort to introduce the corresponding experience.
Abilities that depend on the presence of specific stimuli to develop are called experience-dependent development, e.g. emotional regulation, a second language and perfect pitch.
Among the different experience-dependent capabilities that develop in early childhood, emotional regulation is hands down the most essential one parents should focus on.
So the most important thing for parents to do is to simply provide a nurturing environment for your child and it will do your child a lot of good.
- 1.Snow CE, Hoefnagel-Hohle M. The Critical Period for Language Acquisition: Evidence from Second Language Learning. Child Development. December 1978:1114. doi:10.2307/1128751
- 2.McLaughlin KA, Sheridan MA, Tibu F, Fox NA, Zeanah CH, Nelson CA III. Causal effects of the early caregiving environment on development of stress response systems in children. Proc Natl Acad Sci USA. April 2015:5637-5642. doi:10.1073/pnas.1423363112
- 3.Daw NW. Critical Periods and Amblyopia. Arch Ophthalmol. April 1998:502. doi:10.1001/archopht.116.4.502
- 4.Levitin DJ, Rogers SE. Absolute pitch: perception, coding, and controversies. Trends in Cognitive Sciences. January 2005:26-33. doi:10.1016/j.tics.2004.11.007
- 5.Gervain J, Vines BW, Chen LM, et al. Valproate reopens critical-period learning of absolute pitch. Front Syst Neurosci. 2013. doi:10.3389/fnsys.2013.00102
- 6.Kral A, Sharma A. Developmental neuroplasticity after cochlear implantation. Trends in Neurosciences. February 2012:111-122. doi:10.1016/j.tins.2011.09.004