 Have you ever seen a baby trying to interact with his or her environment? They can't do much when they're very young. They lie on their backs a lot, and maybe they kick their legs and wave their arms. But they can't quote Shakespeare or run an obstacle course. They can't even do basic things like feed themselves or say hello. But as they grow, babies change and become more capable. They're able to feed themselves and carry on conversations. They learn to count and to play baseball and some eventually will be able to quote Shakespeare or run an obstacle course. Human development is the way that people grow and change over time. There are many types of development, physical, cognitive, emotional and social, just to name a few. And while humans develop throughout their entire lives, a lot of momentous changes happen in the first two years of life. Let's look closer at how brain development in the first two years of life influence important motor and sensory developmental milestones. Brain development is a type of physical development. It is the cornerstone of many other types of development. As the brain grows and changes, it causes changes in other parts of the baby's life, too. Suddenly, things that weren't possible before, like clapping or shaking a rattle, become possible because the brain has developed to the point where the baby can perform these tasks. Many people imagine that brain development only involves the brain getting larger. While the brain does get somewhat bigger in the first two years of life, the more dramatic changes don't involve growth in physical size but in functionality. Neuroplasticity, or the brain's capacity to change and adapt, is incredibly high in infancy. As a result, a baby's brain learns new ways to work and function. Imagine for a moment that you have a lump of clay in front of you. Right now, it's just a lump of clay. It doesn't do anything or mean anything. But what if you sculpt that clay into a bowl? Now it's no longer just clay. Now it's something that you can use. You don't have more clay than you did when it was just a lump, but the way the clay is shaped has made it more functional. Brain development is kind of like that. In the first two years of life, neuroplasticity causes the brain to be better and better at simple things. The brain is becoming more and more functional. Two parts of the brain that develop and become better and better at their jobs are the sensory cortex and the motor cortex. These two areas of the brain are in charge of how we interact with the world around us. Think of them kind of like a telephone. The sensory cortex is in charge of figuring out the world through sensory input. It's like the earpiece of a telephone. Information is coming in and is processed in the sensory cortex. The motor cortex, on the other hand, allows us to control the movement of our bodies. It's like the speaker part of the telephone. Information goes out into the world. The sensory and motor cortices work together. For example, if I put my hand near a hot stove, the sensory cortex of my brain registers that it's hot and the motor cortex pulls my hand away. Because they work together, they are close to each other in the brain. They are kind of like a wide headband that stretches across the surface of your brain from one ear to the other. Like other areas of the brain, the sensory and motor cortices develop rapidly in the first two years of life. As you would expect, this leads to several important developmental milestones. Though every child develops at their own pace, there are some things that are common in many infants at different points. For example, at around two months old, a child can hold his head up and follow movement with his eyes. This is important because it marks the beginning of when the child is able to use his motor skills, holding his head up and moving his eyes, to gather sensory information about the world around him. The ability to coordinate sensory and motor movement continues, and by four months old, the baby can use his hands and eyes together. For example, the baby can look at something and then pick it up. By nine months old, the baby is copying sounds and gestures of others. This indicates that his sensory cortex is able to process information and his motor cortex is able to respond. By this time, he can also usually sit up, which gives him even more perspective on the world around him. He might even be able to stand if he's supported. When a baby is around one year old, he can usually stand unsupported and maybe take a couple of steps. By a year and a half, most babies can walk on their own. This is an important moment because being able to walk allows the baby to explore more territory than he could when he was stationary or crawling. Now he can really absorb all that's going on in his environment. If he's in the living room and his mother is in the kitchen, he can walk into the kitchen to see what's going on there. More than ever before, he can use his motor skills to direct his own learning. As you can see, the motor and sensory development of children are closely tied to each other, and they, in turn, influence other types of development, including intellectual, spatial, and emotional. Human development is the process of growth and change that all humans go through. Brain development involves the brain's physical changes. In the first two years of life, the brain grows larger and is also more functional. A key part of this brain development is the development of the sensory and motor cortices, which can lead to important milestones in the way a child interacts with and learns from the world around him.