Early Sensory Input Shapes Brain's Neural Structure

Article excerpt

NEW YORK -- The basic structure of the mind and personality are formed early in life and are resistant to change in adulthood. Those tenets are fundamental and represent the therapeutic challenges of psychoanalysis.

A growing body of research explains such facts of mental life in the neurobiologic processes that shape the brain, Bruce Wexler, M.D., said at a meeting sponsored by the American Psychoanalytic Association.

Sensory input plays an essential role in brain development: By promoting connections between neurons, experience organizes the brain into functional units that govern everything from sensory perception to ways of thinking. In the absence of such stimulation, neurons atrophy.

"No one can say early experience isn't important in shaping the brain," said Dr. Wexler, professor of psychiatry at Yale University, New Haven. If parts of the brain are damaged or removed early in life, other areas can assume its function in the presence of appropriate stimulation. But this neuroplasticity declines sharply after a "critical period" that ends with sexual maturity.

The shaping process applies to higher functions of the frontal and parietal lobes: Animal studies link an enriched sensory environment to greater protein synthesis in the cortex, and an increase in axonal and dendritic branching among its neurons.

Neuroplasticity is particularly prominent in structuring the human brain, the result of a long developmental period, the dominance of cortical areas that are highly responsive to sensory shaping, and the uniquely human ability to alter the environment, Dr. Wexler said.

The social environment--sensory input in the form of human beings and their creations--shapes neural structures that underlie psychological life, he said. Within hours after birth, the infant is visually sensitive to the human face; within days, it can distinguish its mother's voice; and within weeks it prefers to look at its mother's face.

Through "instrumental parenting," caregivers create an environment that modulates the infant's neurophysiology and guides the development of motor and cognitive functions. "In no other species do adults interact moment to moment with infant activity," Dr. Wexler said.

"The child operates within a structure provided by the mind of the adult." By managing the child's sensory input, "parental frontal lobe function shapes the development of the child's frontal lobes ... shaping a wide range of high-level cognitive structures and operations--ways of thinking and planning, values, and preferences," he said.

Imitation, which is more prominent in human than animal behavior, plays a key role. …