Synaptic Competition
I just read Creating Mind: How the Brain Works by John Dowling. A lot of the book was just about basic brain workings, but I did find one part interesting. Apparently when we are born the brain is wired up for all possibilities, but there is a critical period where we lose any abilties that we do not take advantage of.
For example, the visual cortex is wired at birth with neurons to receive input from both eyes. If one eye is not functioning properly during early ages, the visual cortex ends up with vastly more neurons responding to the good eye. However if the eye is injured after this critical period, little change occurs. It is also difficult to reverse this effect afterward as well. Dowling theorizes that this happens because the neurons from the two eyes are “competing” for synapses in the visual cortex during this critical period. When one eye stops sending signals the other eye starts to win more synapses from the visual cortex.
It’s very interesting that during this critical period of development you literally must “use it or lose it.” They’ve found this in many different areas. If you don’t use your left eye during the critical period you will lose the ability to use it. When children are born they can easily discern all sounds and make all sounds but they lose the ability to discern and speak the ones they don’t use (apparently most adult Japanese speakers cannot discern l from r). This is the reason why it is so hard to learn a foreign language when you are an adult. In humans the critical period is from 6 months old to about 6 years old. Dowling suggests that we need to provide our children with full and rich environments so they don’t lose any skills.
Here’s a quote from the book to summarize:
“The conclusion is that the circuitry necessary to carry out complex neural tasks is formed during brain development. But at least some of it is labile, which means it has to be used if it is going to be retained.”
It’s scary that what we do at such a young age can have a such a profound effect on our brains. I wonder what abilities we are born with that we lose because they’re not used during that time….
August 4th, 2006 at 1:42 pm
Monika read my post and thought it was wrong because people can learn to use their eyes later in life, people brain’s do adapt, etc. I am not trying to say that it is impossible to learn after age 6. Obviously there is plasticity in the brain, the recovery of many stroke patients is remarkable.
The experiments that Dowling talks about show that there is this period where you will lose these abilities if you dont use them. It is much harder to lose them afterward and much harder to recover them. For example, he says “If in a young animal a closed eyelid is opened after a short period of deprivation, little recovery is observed after months to years of the eye remaining open.” A trick that ophthalmologists have learned is to put a patch over the good eye so the bad eye can gain more neurons in the visual cortex.
Anyway so the point is not that we lose these abilities permanently, we can obviously re-learn them. But its much easier to use them when your brain is first wired for them than to lose them and have to re-learn them later.