Summer 1995 Volume 4, Number 3

Genes and Learning

You can't teach an old dog new tricks, the saying goes. Learning a foreign language or picking up rollerblading seems natural to a child but gets increasingly difficult in adults. Why?

Learning reflects long-term changes in the connections, or synapses, between brain cells, and neuroscientists have long tried to learn the reason that the synapses of the immature brain are much more "plastic" (affected by experience) than adult brain. For instance, there is only a restricted window of time during development -- the so-called critical period -- when synaptic connections in the visual cortex can be modified by visual experience

One major clue may be in the genetic instructions for a sort of gateway between the surfaces and interiors of individual neurons which responds to the neurotransmitter glutamate. Called an NMDA receptor, this gateway, or ion channel, plays a key role in determining changes in synaptic strength and connectivity when learning takes place.

Genes encode the molecules that make up brain cell components, and recent work by Morgan Sheng of the Howard Hughes Medical Institute and Massachusetts General Hospital has shown that the molecular components of the NMDA receptor actually change during brain development -- in a way that could account for the loss of plasticity that accompanies maturation. Thus, switches in gene expression in the nervous system may contribute to differences in learning ability between young and adult brains.

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