Brain Stem Cells, the Birth of New Neurons, and Their Role in Cognition

While most neurons in the adult central nervous system (CNS) are terminally differentiated, evidence now exists that small populations of neurons are generated in the adult olfactory bulb and hippocampus. In the adult hippocampus, newly born neurons originate from putative stem cells that exist in the subgranular zone of the dentate gyrus. Progeny of these putative stem cells differentiate into neurons in the granular layer within a month of the cells' birth, and this late neurogenesis continues throughout the adult life of all mammals. Stem cells can be harvested from a variety of brain and spinal cord regions, genetically modified, and transplanted back to the brain and spinal cord where they can differentiate into mature glia and neurons depending on the local environment. In addition, environmental stimulation can differentially affect the proliferation, migration, and differentiation of these cells in vivo. These environmentally induced changes in the structural organization of the hippocampus, result in changes in electrophysiological responses in the hippocampus, as well as in hippocampal related behaviors. We are studying the cellular, molecular, as well as environmental influences that regulate neurogenesis in the adult brain and spinal cord. We have recently identified several novel mechanisms that regulate proliferation, survival and differentiation of these adult derived stem cells. The functional and practical significance of these findings will be discussed in light of their implications for alternative or expanded views of structural plasticity in the adult brain.