Differential expansion of neural prosection systems in primate brain evolution

WHOLE brain MRI scans from 11 primate species (43 individuals) spanning mor e than a 50-fold range in brain volume were used to determine whether the c orpus callosum keeps pace with the growth of the forebrain among living ant hropoid primates. Interhemispheric connectivity via the corpus callosum and anterior commissure was reduced in larger primate brains, whereas intrahem ispheric connectivity was augmented. We also show that the splenium constit utes an increasing proportion of callosal area with increasing brain size, This may function to maintain rapid integration of the left and right visua l space as brain size increases. These results indicate that the evolution of larger brain size in primates results in increasingly independent hemisp heres, NeuroReport 10:1453-1459 (C) 1999 Lippincott Williams & Wilkins.