The Neurogenesis of Thought
‘‘I think, therefore I am,’’ a famous dictum attributed to the 17 century philosopher René Descartes, is deceptively simple, yet the biology at the heart of it is so overwhelmingly complex that it boggles the mind. Cognitive thought is a fundamental aspect of human existence, and the neural underpinnings of this fascinating ability have captivated inquisitive minds for centuries. In this exciting age of modern neuroscience, great progress is being made in understanding the neurobiology of thought from cellular, molecular, developmental, evolutionary, and systems neuroscience perspectives. The brain is often considered the most complex organ. Within the brain, the cerebral cortex is the region responsible for higher thought processes. The building of the cerebral cortex is an intricate process requiring a beautifully orchestrated program where billions of neurons are generated and assembled into complex circuits at the right time and place and with the right functional specializations. While much has been learned aboutmammalian neurogenesis and cortex development from rodent models, there are fundamental differences between mice and humans that have made understanding uniquely human cognitive abilities challenging. The human cerebral cortex is characterized by two unique features: its unusual size relative not only to the rest of the brain, but also to overall body size, as well as its level of gyrification, or cortical folding, which is thought to increase surface area. Both of these aspects are thought to be important for higher human cognitive abilities. These limitations have prompted researchers to look beyond the mouse to understand the mechanisms at play allowing for expanded cerebral cortex size.