• by Gord Hotchkiss , Featured Contributor, January 24, 2008

In 1986, University of Virginia Psychologist Daniel Wegner came up with an interesting theory. He realized that we depend on others to remember some of the things we need to know. This is especially true in couples and families. Some of us are better at remembering phone numbers and birth dates. Some of us are better at remembering how 401Ks and computers work. In couples, the longer we spend together, the more we divvy up the memory workload, depending on our spouse to prop up our spotty memories.

Wegner called this transactive memory. With it, we don't have to remember everything. We just have to remember who knows what. Wegner found this to be true in any small group who spends a lot of time together. The bigger the group, the larger the extended memory capacity.

That's the first concept I want you to think about. Now, let me give you another.

It's the Second Chimp on the Left, the One with the Scar

Babies are born with a capability that you and I don't have. They can recognize and distinguish between faces of different species. For example, if you introduce a 6-month-old baby to six different chimpanzees, then show them pictures of the chimp faces, they'll be able to recognize them and tell them apart. But to us, they will all look like chimpanzees. The same is true of sheep, or lemurs. To us, a sheep is a sheep is a sheep. It seems we lose this ability around 9 months of age, according to Olivier Pascalis at the University of Sheffield.

Why can we no longer tell chimpanzees apart? We're born with this ability because at one point in our evolution it was important. The ability to tell animals apart led to a greater chance of survival. But that's not really true today. Today, in our complex social world, it's much more important to be able to tell human faces apart. So at about 9 months of age, the brain starts to concentrate on that. And, in this case, something has to give. Sorry chimps, but after a while, you'll all look the same to us.

There's one more point I want to share here. Dr. Pascalis found that if parents continued to develop their babies' ability to distinguish between non-human faces by repeating the exercise, the babies retained that skill.

The Pruning of the Young Mind

It's not so much this lost ability I find interesting. It's the underlying reason, the ability for the brain to change itself from birth to maturity. Humans received another gift in the evolutionary lottery, an adaptable mind. The brain you get at birth is not the brain you'll end up with. A 2007 study at Oxford University found that newborn brains have almost 50% more neurons than adult brains. Babies have more raw "brain material" to work with. They get shipped with the full menu of evolutionary options, including the ability to tell monkeys apart.

But over time, in a process known as "pruning," the brain starts to discard options it doesn't use very often. Weak, underutilized neurons, forming neural pathways we never use, get pruned and, in some cases, reconfigured, to make way for pathways that are more commonly used. To go back to our facial recognition example, being able to keep track of all the faces in one's ever increasing circle of friends and family is a huge task. And it's right around 9 months that we start venturing out in the world, meeting more and more people. The timing of this is not coincidental.

Fertilized Neurons

But our brains not only get rid of unused functions. They also nurture commonly used functions. The same Oxford study found that although our neuron inventory decreases, we actually gain significantly in another type of cell -- glials. Glials are the most important brain cell you've probably never heard of. They act as a support system for our neurons, nurturing them and making them more effective. And adults apparently have three times the number of glial cells found in infants.

So, for the next seven days, until my next column, I want you to think about those two concepts: we rely on external sources to extend our memory, and our brains are adaptable, able to rewire themselves to discard capabilities that are no longer important to us, and build capabilities that are more important.

See where I'm going with this? Until next week...