 Brain development begins just a few weeks after conception, so many critical brain regions develop in utero. At birth, the human brain has developed most of its neurons and wired them together in precise ways. For example, the corpus callosum starts developing at about 12 weeks gestation and continues to develop even after birth. The corpus callosum is the largest fibre tract in the brain. It connects the left and right cerebral hemispheres. In 1981, Roger Sperry shared the Nobel Prize in Physiology or Medicine for his work on understanding the function of the corpus callosum. He studied patients that had had their corpus callosum surgically severed to control epileptic seizures from travelling from one side of the brain to the other. These patients had difficulty integrating information from each side of the body. Sperry called this split brain syndrome. However, some people are born with an absent or malformed corpus callosum and these people have vastly different cognitive outcomes to people with the split brain syndrome. Malformation of the corpus callosum can occur in isolation as the only deficit or it can accompany a range of developmental problems in other organ systems. Therefore, people with these disorders can have a variety of symptoms ranging from severe to more mild intellectual, physical and sensory disabilities. But in addition to offering support and information to parents and individuals concerned our increased understanding of the corpus callosum also has implications for our understanding of brain plasticity. The concept of brain plasticity has received a lot of attention in recent times. Brain plasticity refers to the capacity of the brain to modify its connections or to reorganize itself throughout a person's lifetime. While neuroscientists talk about plasticity, psychologists talk about learning. Neuroscientists look at the hardware, how the structure and function of synapses change with experience. Psychologists look at how these brain changes express themselves in behavior. But the two fields can inform one another in ways that can be really useful for understanding learning. From a neuroscience perspective, the classic form of plasticity operates at the synapse. The tiny gap between nerve cells across which neurotransmitters pass. If one nerve cell fires and activates another neuron in the chain and that happens repeatedly, there'll be a stronger relationship between those two cells. This means that over time, for one nerve cell to activate or communicate with another one less and less juice will be required to complete the same action. We teach our students to remember this with the phrase, neurons that fire together wire together. But there's a flip side to this with its own little catchphrase, neurons out of sync lose their link. If the pattern of firing between neurons is infrequent or random, then those neurons don't tend to fire together in the future. So plasticity is two-sided. One side greases the wheels for things that do happen often, while the other side does the opposite for things that don't happen very often. Plasticity isn't just about enhancement, but also about inhibition. The brain is highly interconnected and all the different parts have to act in concert with one another. The term brain plasticity refers to the idea that the brain can change when making new functional and structural connections between neurons or brain cells. However, why we definitely do have plasticity in our brain? The idea of cells making connections through task exposure and training doesn't necessarily capture the whole complex pattern of what's happening in the brain during learning. There's different types of learning, too. Motor memory or procedural learning involves learning skills like a specific sequence of actions such as that involved in playing an instrument. This is different from the kind of learning involved when learning to read. So when we talk about how the brain works and what's happening during learning, it's not a simple, orderly story. The brain is a very messy, complex, highly interactive and highly interconnected processing system. The way that the brain compensates for a malformed corpus callosum illustrates a kind of brain plasticity that is different to the more common understanding of synaptic plasticity. The fibres that normally cross the corpus callosum find a different route to connect the two hemispheres. This is called axonal plasticity. Would-be callosal fibres grow in a new direction across a different tract during development. The value of this research lies in its potential to help us understand how optimal brain wiring could be achieved, giving people the chance to reach their full potential. Certainly, there are parts of the brain that are critically involved in learning, like the hippocampus, which is involved in memory. While teachers don't necessarily need to know the details, it is useful for teachers to have some knowledge about how the brain works, because this can potentially enhance the planning and management of classroom activities to support deep learning.