FIGURE 1.9 Birth of a Neuron A decade ago neuroscientists thought that adult brains lost neurons, with age or alcohol, but never gained them. Now we know that precursors of neurons arise in the lateral ventricles (bright blue, center) to become functioning neurons in the olfactory bulb (for smell, far left) and the hippocampus (for memory, the brown structure just above the brain stem). Adult neurogenesis is much less prolific than earlier in life, but the fact that it occurs at all is astounding.