Synaptic pruning, a process that was thought to occur only during childhood, has recently been discovered to continue all throughout the early 20s of adulthood.
During childhood, the human brain tends to overproduce connections between brain cells. These connections are known as synapses. Upon puberty, approximately half of these synapses are removed, while others are strengthened. This gives rise to the mature, cognitive identity that each of us has. Scientists have long held the belief that synaptic pruning stops at the end of puberty. Recent research done by Pasko Rakic of Yale University might just lead us to question that conclusion.
Analyzing post-mortem tissue from the pre-frontal cortex of subjects ranging from 1 week to 91 years of age, Rakic and his team calculated the density of dendritic spines. These structures are small projections located at the end of neuronal dendrites. Dendritic spines carry out synaptic communication with other neurons.
Rakic’s investigation revealed that dendritic spine density increases rapidly while we are infants, peaking around our ninth birthdays, after which synaptic pruning begins. However, spine density did not remain constant after puberty. Instead, it continued decrease slowly as subjects went through their 20s.
Synaptic pruning is typically associated with an increased ability to learn and pick up new skills. As such, Rakic predicts that a high possibility for people to learn new languages or grasp new concepts till their third decade in life. He says, “You should not give up learning just because you’re in your 20s - it isn’t too late.”
The discovery of this aspect of synaptic pruning is also likely to interest researchers involved in brain degenerative diseases. Sabine Bahn, a researcher from the University of Cambridge, believes schizophrenia is a disease that has both developmental and degenerative causes. Elena Badgely from the University of Sydney, feels similarly. She comments that the pre-frontal cortex is “susceptible for longer to disorders and disease that result from abnormal pruning.” As such, Badgely speculates that synaptic pruning might have a hand in memory loss and dementia.