En route to a human brain
What keeps you from telling your boss exactly what you think of him? It's probably your frontal cortex, a brain region involved in selecting appropriate behaviors for environmental circumstances. Patients with damage to the frontal cortex may fail to follow social rules and often choose short-term rewards over long-term gain. In humans, the frontal cortex is greatly enlarged compared with the same structure in other mammals (even other primates). Many brain regions that connect with the cortex, subdivisions of the thalamus in particular, are also bigger.
A new study by Letinic and Rakic of Yale University now offers some important clues as to how such a coordinated expansion of brain areas may arise during embryonic development (Nature Neuroscience, Vol. 4, No. 9, Sep 01). The authors measured patterns of neuronal migration in cultures of live human brain tissue and repeated the same experiments with similar cultures from monkey and mouse brains. Migration is fundamental to brain development, as neurons often travel far from where they are born to their adult positions. By placing a dye in the telencephalon (which gives rise to the cerebral cortex), the authors were able directly to detect migrating neurons en route to a subdivision of the thalamus in the human tissue (notably a region that is connected with the frontal cortex and is particularly enlarged in humans). Despite the otherwise high degree of similarity in developmental mechanisms across all animals, such a migrating stream of cells was not apparent in the monkey or mouse brain. Furthermore, the authors demonstrated that cells of the human thalamus attract migrating telencephalic cells, whereas cells from monkey or mouse thalamus inhibit migrating cells. These data suggest that during evolution, a change in guidance cues may have allowed for the appearance of a new migratory pathway - and thus contributed to the coordinated expansion of the human brain.
Yi Rao and Jane Wu discuss this work in an accompanying News and Views article.
Dr. Pasko Rakic
Section of Neurobiology
Yale University School of Medicine
333 Cedar Street
PO Box 208001
New Haven, Connecticut 06510-8001
tel: +1 203-785-4330
fax: +1 203-785-5263
Dr. Yi Rao
Washington University School of Medicine
Department of Anatomy and Neurobiology
660 S. Euclid Avenue
St. Louis, Missouri 63110
tel: +1 314-362-9388
fax: +1 314-362-3446
(C) Nature Neuroscience press release.
Message posted by: Trevor M. D'Souza
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