The infant brain is changeable and plastic. Sensory stimulation produces the very connectedness and function that in turn make normal consciousness possible. For this reason, sensory deprivation may produce permanent damage. Hubel and Wiesel showed this by rearing cats in the dark; what they demonstrated was that cats deprived of sight during a critical period in infancy would never be able to see. The neonatal mammal, we learn, is plastic and open; in a very real sense the environment itself produces in us the conditions needed to experience the environment. They also showed that there are limits to the brain’s plasticity.
Of special importance to the child’s neurological development is its relationship to other people. Consider a question explored by Bruce Wexler in an excellent recent book on this topic: Why do mammals suckle at the breast? To get food, to be sure, but also to get touch - that is, to get the stimulation that is itself necessary sustenance for the developing brain. […]
Mothers or other primary caretakers do not merely take care of their young. A two-way exchange arises between child and mother that provides the setting within which the child develops both physiologically and psychologically. A child learns to restore its own calm or comfort by being calmed or comforted by the mother. The child’s basic physiological processes - burping, for example - are facilitated for the baby by the mother. The caretaker manipulates the child’s posture, raising her into a sitting position, now setting her down in a prone position, either to arouse the child or prepare her for sleep. …The mother’s attentiveness to the needs of the child teaches the child to learn to manage her own needs. In a very real sense, the baby-caretaker “dyad” is a unity from which the child only gradually emerges as an individual. We can speak of attachment here, but I prefer to speak of oneness. Our seperation from our mother-figure is, in some respects - for most of us, anyway - only partial; in any event, there is for us no such thing as complete detachment from the community of others and from the larger environmental structures and situations - lights, sounds, odors, the ground, the air, technology - up against which we first become ourselves.
Maturation is not so much a process of self-individuation and detachment as it is one of growing comfortably into one’s environmental situation. We grow apart, but we attach to the world without. We integrate. In learning to walk or mastering language, in developing friendships, in acquiring an occupation, in learning to navigate and use technology, we root ourselves in the practical environment. This is one reason, certainly, why radical changes to one’s environment, especially occurring later in one’s life - for example, in the course of migrating from one country to another, upon the loss of a spouse, during a period of rapid technological change - are enormous, maybe even devastating personal challenges. The loss of a feature of the environment with which one’s daily activities are intimately interwoven is the loss of a part of oneself.
The point is no that you can’t teach an old dog new tricks: sometimes you can. The point really is that to do so, you need to make the dog new again. Someone once told me that it’s good to change jobs every seven years or so. It keeps you young. One explanation for this might be that changes force you to renew yourself by developing anew in relation to new external structures, new habits, new modes of involvement with the world around you. Another effect of this kind of disruption is that time, in an interesting, felt way, slows down. When life is routinized, days and weeks and months blend into one another: each day is like the next; days form an arc as one’s life project unfolds. But when routine is disrupted - when you move, or even when you travel - days acquire a distinct specialness. …
We see something like this very dynamic in the development of a young person. A summer can seem like a magical eternity to a child. Think of the play and sweat and swimming and books and people and shopping and long evenings! But getting older requires one to channel one’s day into a structure of meaning, into a plan; under the shadow cast by one’s projects, life acquires an organization that in a way removes surprise. To grow old is to give up surprises; to insists on surprises, is in a way, to stay young. This may be one reason why we have kids.
Noë, Alva. Out of our Heads: Why You Are Not Your Brain, and Other Lessons from the Biology of Consciousness. New York: Hill and Wang, 2009. 49-52.