You have fewer synapses in your brain now than a 2-year-old. That may sound like an insult, but it’s a scientific fact. We’re all born with heads full of lonely, isolated neurons. But as our baby brains are inundated with sensory information over the first two years of life, those neurons rapidly form connections, or synapses. A toddlers’ brain teems with more than 100 trillion of them. By the time that toddler becomes an adult, though, the brain will have pared back roughly half of them — synapses that are used frequently become stronger, while those that aren’t wither away.
This process of overproduction followed by winnowing allows the brain to shape itself to its environment. As neuroscientist David Eagleman writes, “You become who you are not because of what grows in your brain, but because of what’s removed.”