by Sue Halpern
Last week, Dr. David Sulzer’s lab at Columbia Medical School reported that researchers were able to reverse the symptoms of autism in mice by administering a drug that prunes synapses. Though scientists have known of the connection between synaptic overload and autism, this was the first time that they have been able to show that pruning synapses is palliative. What might seem counterintuitive that the human brain needs to shed neurons to develop normally, that, in fact, is what needs to happen between birth and puberty. Think of it as clearing out the attic so you can make clear pathways to what you’ve got stored up there. (When you read Bill’s post, One Perfect Thing, you will understand why this analogy seems especially apt to me today.) More to the point, many of the 100 billion neurons we are born with are not yet connected. As neurons are shed, there is more and more room for connections to be made. According to one source I read, at birth, each neuron has about 2500 synaptic connections and by three that number has grown to about 15,000, and continues to increase exponentially. According to another,
At birth the baby has 50 trillion connections or synapses
In the first three months of life, the synapses multiply more than 20 times
At one year the brain has 1,000 trillion synapses.
The takeaway, here, numbers aside, is that as neurons are shed, connections are made.
So I was particularly interested in Ferris Jabr’s explanation for why we forget childhood memories, which in the end may turn out to be a very good thing:
Studies have shown that people can retrieve at least some childhood memories by responding to specific prompts—dredging up the earliest recollection associated with the word “milk,” for example—or by imagining a house, school, or specific location tied to a certain age and allowing the relevant memories to bubble up on their own.
But even if we manage to untangle a few distinct memories that survive the tumultuous cycles of growth and decay in the infant brain, we can never fully trust them; some of them might be partly or entirely fabricated. Through her pioneering research, Elizabeth Loftus of the University of California, Irvine has demonstrated that our earliest memories in particular are often insoluble blends of genuine recollections, narratives we sponged up from others, and imaginary scenes dreamt up by the subconscious.
In one set of groundbreaking experiments conducted in 1995, Loftus and her colleagues presented volunteers with short stories about their childhood provided by relatives. Unbeknownst to the study participants, one of these stories—about being lost in a mall at age 5—was mostly fiction. Yet a quarter of the volunteers said they had a memory of the experience. And even when they were told that one of the stories they had read was invented, some participants failed to realize it was the lost-in-a-mall story.