0
1
Images In Neuroscience   |    
Brain Development, XPruning During Development
PHILIP SEEMAN, M.D., PH.D.
Am J Psychiatry 1999;156:168-168.
Human brain size changes little over the child and teen years. Nonetheless, considerable cellular and functional change occurs. These maturational changes result in an adult functioning brain and are subject to developmental influence. The images above serve to illustrate this. Figure A shows that at birth, cellular elements are still entering the cortex. By midchildhood, more neurons and more cellular processes are established than in adult years. The developmental task of childhood years from an anatomic point of view is to prune and to select the most useful (perhaps the most used) neurons, synapses, and dendrites to preserve for the adult brain. This process of pruning continues through the early teen years. Presumably, the pruning is accomplished "wisely." This would mean that synapses that are most important to survival and optimal function flourish whereas useless connections vanish.
One marker of neuronal number is the density of neurotransmitter receptors. In figure B, the density of the dopamine D2 receptor is graphed over a wide age range, beginning immediately after birth and extending to the ninth decade. This graph illustrates the high density of D2 receptors before 5 years of age, a density greater than adult levels, and their regression to adult levels reached during the second decade. Dopamine receptors continue to decrease in adult years, but at a considerably slower rate of 2.2% reduction per decade. This rate is faster in males than in females. But the decrease is slower overall than the tremendous childhood increase in number. In schizophrenia, the rate of D2 receptor loss is faster than in healthy comparison subjects: a 1.9% loss per decade in comparison men and a 6.0% loss per decade in men with schizophrenia.
These data suggest that while certain fixed processes establish the availability of CNS neurons, other influences generated by the organism and the environment serve to determine neuronal survival and connectivity.
Figure A courtesy of Dr. Seeman.
 
Anchor for JumpAnchor for Jump
Left Figure
Proliferation and decline in synaptic connections in children
Right Figure
Reproduced from Seeman et al.: Human Brain Dopamine Receptors in Children and Aging Adults. Synapse 1987; 1:399–404. Copyright " 1987, Wiley-Liss, Inc., a division of John Wiley and Sons, Inc. Reprinted by permission of John Wiley and Sons, Inc.

Left Figure

Proliferation and decline in synaptic connections in children

Right Figure

Reproduced from Seeman et al.: Human Brain Dopamine Receptors in Children and Aging Adults. Synapse 1987; 1:399–404. Copyright " 1987, Wiley-Liss, Inc., a division of John Wiley and Sons, Inc. Reprinted by permission of John Wiley and Sons, Inc.

+
+
+

CME Activity

There is currently no quiz available for this resource. Please click here to go to the CME page to find another.
Submit a Comments
Please read the other comments before you post yours. Contributors must reveal any conflict of interest.
Comments are moderated and will appear on the site at the discertion of JBJS editorial staff.

* = Required Field
(if multiple authors, separate names by comma)
Example: John Doe



Related Content
Articles
Topic Collections
Psychiatric News
PubMed Articles