BY BEVERLY J. RODER, Ph.D. and MABEL L. SGAN, Ph.D.
By applying MRI technology to the study of brain maturation, Paul Thompson and his fellow researchers have found a way to visualize the continuous growth of the developing brain. Their technique combines repeated MRI scans of children's brains to produce 4-dimensional images showing actual changes over time. Their main focus was the corpus callosum,a fibrous structure across which the two hemispheres communicate. As portions of the corpus callosum grow and change, those changes are reflected in the parts of the brain they serve.
Initial 3-dimensional MRI scans of 3-15 year-old children were repeated at intervals up to 4 years, then merged to create the image of a developing brain. Although no changes were noticeable over short (2 week) intervals, trackings over 3-4 year periods revealed a striking front-to-back growth wave.
The most rapid growth between 3 and 6 years took place at the part of the corpus callosum that connects to brain areas regulating mental alertness and organization. This finding provides a physiological explanation for the rapid development of planning skills in pre-schoolers. In contrast, repeated trackings of children 6-13 years showed the growth wave moving toward an area of the corpus callosum connected to centers for language and mathematical thought. Note that this coincides with the time when children are making rapid strides in reading, math, and making associations between verbal concepts.
Most interesting of all, trackings made from older children (11-15) showed that growth was beginning to diminish just as connecting brain cells in language areas began deteriorating. The authors point out a link between this neurological slow-down and the theory of a critical period for language learning that ends at puberty. We've known for some time that language learning is more difficult after puberty than before and that those rare children who have not been exposed to any language prior to this time never fully master it. These finding provide a physiologic foundation for that theory. The discovery of a similar loss of brain tissue (a 50% by early adolescence) in areas supporting motor behaviors such as riding a bicycle or playing the piano raises the intriguing possibility that there may be a critical period for learning motor skills as well. [Thompson, P.M., Giedd, J.N., Woods, R.P., MacDonald, D., Evans, A.C., Toga, A.W. (2000). Nature, 404, 190-193.] (c) 2000 Dr. Beverly J. Roder and Dr. Mabel L. Sgan.