This phrase is taken from the cover article of the New Scientist, 21 Feb 2015, “Meet Your Other Brain”, 30-33 by Ted Burrell. Grey matter in the brain is grey due to myelin. At one time it was thought that the main purpose of myelin was to speed up reflexes to so we could react faster. However, William Richardson who studies neural plasticity at University College, London said that “Ultimately it allows us to have clever brains.” A small amount of myelin is made while we are still in the womb, but after birth it takes off . It surges as infants learn to crawl, walk, and talk. At around age 4, the rate of myelination slows and teenagers still have the prefrontal cortex left to myelinate. The prefrontal cortex is crucial for planning and consideration of consequences. Consequently, processing in the prefrontal cortex is slow and inefficient and teens remain impulsive. By the time we reach our forties, during which there have been many opportunities to ruin our lives, the final circuitry is completed. But from our 60s onwards the coverings start to fray and degenerate, which fits the common experience of cognitive decline as we age. As myelin degenerates, the signals get fuzzier.
Neural plasticity is at the neurons and the synapses between them. The number of neurotransmitter receptors increase in a synapse the more the pathway is used, which enables the brain to adapt according to learning or experience. Consequently, our quest to understand cognitive decline, and the potential for activities that boost brain power has focused on grey matter, the part of the brain and spinal cord packed with the neurons cell bodies and synapses.
It wasn’t until 2009 that the new neuroimaging method called diffusion MRI was available that allows measures of human white matter in the living brain. Heidi Johansen-Berg of the University of Oxford examined a 2004 study, which found that learning a new skill such as juggling changed the density of grey matter, which is an example of classic synaptic plasticity. She replicated this juggling study and found that after six weeks brain scans showed that myelin had increased more than that of a control group who had no training (Nature Neuroscience, 12, p. 1370). She found the change not only in the grey matter but also in the underlying white matter pathways, which suggested that these pathways strengthen in some way as the result of experience. These changes in white and grey matter took place over different timescales, which suggested two different processes. Johansen-Berg thinks that the increase in white matter would have enabled faster conduction along the circuits coordinating juggling. This effect was seen in everyone who learned to juggle, regardless of how well they learned to juggle, implying that it is the learning process itself that is responsible.
Myelin is formed by oligodendrocytes, which are octopus-shaped cells with long arms that wrap thin layers of fat 50 to 100 times around an axon, preventing electrical signals from slipping out and expediting the conversation between brain regions. These cells are made throughout life by oligodendrocyte precursor cells (OPCs), that tile the brain, ready to morph at moment;s notice.
Myelin plasticity is a second type of plasticity distinct from the well-known synaptic plasticity. More studies are needed with human subjects, but the animal studies have important implications for learning and memory. Well-used pathways get more myelin, speeding up the signals and making the brain more efficient. Gabriel Gorfas of the University of Michigan says, “it’s not only that the information is stored in the plasticity of the synapses but actually in the myelin as well. For instance, if you are learning Mandarin, myelination would help you remember the right character faster and more intuitively. This gives a new dimension to the amount of information and the toes of information the nervous system can store. The importance of these and other non-neuronal cells has led to the term our “other brain.””
Myelin information can also be lost. The brain is a use it or lose it organ. “If electricity isn’t flowing, the myelin can degrade, and this can lead to psychological and social problems. If the brain were a city, and myelin the insulation, some parts would end up in the dark. A lack of myelin is implicated in conditions like autism, and in mental illnesses such as schizophrenia, and in spinal cord and traumatic brain injuries.”
So the bottom line is, “Keep learning, keep your mind active,” Learning new things is recommended, like a new piano piece (assuming that you do play the piano), keep up with ordinary activities like talking a walk. If it’s an unfamiliar route, with changing scenery, and the requirement t learn the way home, all the better. Take a new hobby, another. The goal is to keep the electricity flowing a little better, a little longer.