The nervous system is a static, hard-wired system, much like your television set. But is neuroanatomy so immutable? Recent studies suggested that it is not. Indeed, the brain appears to be a highly dynamic system capable of enormous plasticity during development and as a result of experience in adults. Perhaps the most exciting new finding is that not only do synapses grow and retract during learning but also new neurons appear to be born in the adult brain after a variety of experiences.
New neurons? That’s right. In mammals, the birth of most neurons, called neurogenesis, occurs early in embryological development while the fetus is still in the uterus. These immature neurons migrate throughout the developing brain, looking for an address that tells them where they will spend the rest of their lives. When they get to that address, each neuron settles down and differentiates into one of the many shapes and sizes. In most cases, these neurons lose their capacity for cell division once they mature into a differentiated neuron. In other words, once cells are born they are not replaced by new generations of cells later in life.
However, recent studies have questioned the long-held view that the adult brain is incapable of producing new generations of neurons. In a recent study, investigators injected rats with a compound called BRDU that labels newly born neurons. After injecting the rats, they trained animals in a classical conditioning task that requires the hippocampus. They found that rats that underwent training in the conditioning task exhibited a significant increase in the number of labeled neurons in the hippocampus (Gould, Beylin, Tanapat, Reeves, & Shors, 1999). Interestingly, training a similar conditioning task that does not require the hippocampus was not associated with the birth of new neurons in the hippocampus. More recently, these investigators have found that drugs that block hippocampal neurogenesis impair trace eyeblink conditioning (Shors et al., 2001). Collectively, these studies suggest not only that learning is associated with the birth of new neurons in the brain but also that neurogenesis may itself be essential for learning to occur. Interestingly, not only complicated learning task induce the birth of new hippocampal neurons. Salk Institute has found that simply giving animals an opportunity to exercise increases the number of newly born hippocampal neurons (Van Praag, KEmpermann, & Gage, 1999). These neurons develop and behave just like adult neurons (van Praag et al., 2002).
So, not only does your daily jog keeps you trim-it fuels your brain’s potential for learning. So, go ahead, treat your brain and run a few miles today!