With current interest in the brain in general, many of us have become more familiar with the vocabulary of neuroscience. For example, we hear about neurotransmitters and synapses in the brain from pharmaceutical advertisements. Popular magazines, websites, and ads offer ways to enhance functions like memory and attention and refer to the brain’s neural plasticity. Much of brain science is seeping into our common language. However, one term that may be less familiar with regard to the developing brain is called a ‘sensitive period of development.

A Sensitive Period of development is defined as a period of time when the brain is maximally sensitive, receptive, or plastic in response to its environment. Environment is a broad construct and can mean how children are parented, what kind of family configuration they grow up in, what they eat, where they live, what they see and hear around them, and what life is like in the larger culture of which they are a part.

The term sensitive period has been applied most often to describe the brain changes of early childhood that affect visual, motor and language development, among others. Typically, brain changes are inferred from changes in behavior seen on the outside- for example, a child’s first steps or first words. But the brain doesn’t just run on automatic pilot and evolve in isolation, apart from the child’s environment.

It turns out that the brain, in its ongoing processes of development, goes through stretches or periods of time or periods when it is sensitive to, and requires, certain kinds of environmental stimulation. This stimulation from the environment essentially ‘feeds the brain’ what it needs in order to support its growth.

One might say that the brain ‘expects’ to be able to see and hear and move, experiences that are typical of most young children, because it needs this visual, auditory and spatial/kinesthetic information to build adaptive brain connections. For example, the brain is built to receive the stimulation of visual input (a parent’s face, a mobile above a crib, etc) and uses this experience to refine visual acuity over the first months of life. Similar processes occur for movement and, across a longer period, for language and cognition. Just like the body needs air and nourishment to survive and grow, the brain needs the stimulation or raw material of its environment in order to build its functions. We call this kind of learning and development, ‘experience-expectant.’ In cases that are thankfully rare, animals and children who are deprived of necessary stimulation to an extreme degree during sensitive periods of development can suffer lifelong impairments in certain functions.

In addition to vision, movement, language and cognitive development, the first years of life are also sensitive periods for the development of attachment to primary caregivers. These periods are ‘sensitive’ precisely because the brain is changing or organizing itself in specific areas that serve these skills, and these skills or competencies emerge in response to stimulation from the child’s environment.