Synaptic pruning: why young brains need to be decluttered

Babies and children learn impressively complicated things through one-on-one interactions with people, play, hands-on explorations, physical movement experiences and sensory experiences.

Written by Lizette van Huyssteen (B.Soc.Sc), Founder of the Practica Programme:

Babies and children learn impressively complicated things through one-on-one interactions with people, play, hands-on explorations, physical movement experiences and sensory experiences.

Unlike adults, they don’t have to consciously apply themselves and intentionally practice when they learn and develop new skills, because a vast overabundance of preliminary pathways develops spontaneously between their brain cells during the first two years. These pathways are already built halfway and ready to be activated into use through experience. (If you missed that post you can read it here.)

When the brain identifies preliminary pathways that are useful and active, it rewards them by wrapping them in a fatty substance (myelin sheaths) to protect and insulate them so that they can transmit signals at a much faster rate. What’s more, the brain interconnects useful pathways with other useful pathways to effectively “hardwire” them into the brain by creating ever-growing and ever-changing brain maps. (If you missed the post about neuroplasticity you can read it here.)

*We know a brain map is forming when a behaviour becomes automatic for a person. Athletes refer to “muscle memory”, behavioural scientists refer to brain maps as “habits” and teachers refer to them as “school readiness skills” or “foundational skills”.

Brain maps inevitably impact on a person’s functioning. Here are 3 examples of how we benefit from having them:

  1. Brain maps that become stronger and more extensively connected account for the vast improvements in the precision and speed of coordinated movements that we see in children’s fine and gross motor skills during the first five to six years of life.1
  2. Socially, a good example of the impact of brain maps is the way in which good (or bad) manners become second nature for young children.
  3. On an educational level, academic school readiness skills are also hardwired into brain maps. As an example, a child who has developed a brain map for number values will automatically think of a number in terms of its position on the number’s line (e.g. six is one bigger than 5 and one smaller than 7) and this point of reference prepares him or her for formal maths.  

Since growing myelin sheaths and bigger brain maps need room to grow, space is a problem in the developing brain.

This explains why a child’s brain needs to continuously “declutter” itself by letting go of more and more of the preliminary pathways. It wisely does so by eliminating brain cell connections that are either weak, dysfunctional, or simply not yet hardwired into the brain.2

This process is called “synaptic pruning” and it zooms in on different parts of the brain at different ages during childhood. It starts at the lower parts where the sensory information that comes from the ears and eyes are perceived and processed, and then slowly progresses upwards and forwards through the brain to increasingly more sophisticated brain regions.3

*By the time a child reaches adulthood, 40 to 50 percent of the preliminary brain cell connections that were available at 2 years of age, and 15% of the original 100 billion brain loose cells that were available at birth, will be eliminated.4

Unfortunately, having less and less preliminary pathways available means that a child’s brain becomes less and less adaptable at every birthday.

It seems unfortunate that synaptic pruning removes excess brain cell connections, since having less preliminary pathways available means losing adaptability and impressionability over time. What’s more, the pruning process is ruthless. For example, in the image above, the brown colour indicates a period during which the adolescent brain is pruned at a rate of an estimated 100 000 brain cell connections per second.5

Initially, the brain is so malleable and impressionable that a small amount of input has a huge impact on how it wires itself. The density of the preliminary pathways reaches its peak at two years of age, when every neuron has forged a whopping 15 000 synapses to loosely connect with thousands of other neurons to provide the brain with trillions of possible options as it wires itself to process incoming signals, store information and control behaviour in ways that align with the demands of the world in which an individual child lives.6

The graph below indicates how an increasing amount of effort is needed over time to positively impact on the growth trajectory of the developing brain.

This process is inevitable because maturing children need to develop brains that can cope with the demands of the adult world.

As children grow older, they have to part with the adaptable version of their developing brains so that they can develop the brain wiring that is needed for them to motivate themselves, focus on a single task for longer periods of time, multitask, plan ahead, self-evaluate, solve higher-level problems and read multiple emotional and social cues at once so that they can respond appropriately in social situations.7

In other words, the upside of synaptic pruning is that it paves the way for the brain to change structurally so that children can grow into independent adults who are intelligent on an adult level, empathetic, responsible, and motivated – ready to be useful in society and equipped to raise children of their own.

*Looking at the way in which the brain instinctively manages inevitable change wisely, it is clear that philosopher Reinhold Niebuhr aligned himself with a deep seated universal truth when he said: “Change is the essence of life; be willing to surrender what you are for what you could become”.


1. Tierney, Adrienne L. and Nelson Charles A. Brain Development and the Role of Experience in the Early Years. Zero Three vol.30(2):9-13 (2009)

2. Kolb, Bryan and Fantie, Bryan D. “Development of the Child’s Brain and Behavior” in book: Handbook of Clinical Child Neuropsychology (Second edition), Chap. 2, Edited by Cecil R. Reynolds, Elaine Fletcher-Janzen, Springer.pp.19-46(2008)

3. Gogtay, Nitin et al. Dynamic mapping of human cortical development during childhood through early adulthood. PNAS, vol. 101,21:8174-9 (2004)

4. Sakai, Jill. Core Concept: How synaptic pruning shapes neural wiring during development and, possibly, in disease. PNAS, vol. 117(28):16096-99 (2020)

5. Feinberg, Irwin and Campbell, Ian. G. Sleep EEG changes during adolescence: an index of a fundamental brain reorganization. Brain Cognition vol. 72(1):56-65 (2010)

6. Huttenlocher, Peter R. Synaptic density in human frontal cortex: Developmental changes and effects of aging. Brain Research, vol. 163:195-205 (1979)

7. Schafer, Dorothy P., et al., Microglia sculpt postnatal neural circuits in an activity and complement-dependent manner. Neuron, vol. 74:691–705 (2012)