Monday, July 16, 2007

Memory and the Development of the Brain

The hippocampus is a "A peninsula-shaped structure in the middle of the brain that is crucial for learning as well as for consolidating long-term explicit memories."

Research suggests that memory during infancy is dependent upon the hippocampus and that at a later age involves additional structures of the brain

In the cortical sensory systems, patterns of synaptic connectivity are formed postnatally. Before the emergence of behavioral function, the organization of synaptic contacts is influenced by sensory experience during a postnatal "sensitive period," resulting in permanent changes in connectivity and function.

Like the sensory cortices, the hippocampus undergoes a period of postnatal development, and behavioral function does not emerge until this period is complete. But, much of hippocampal synaptogenesis occurs postnatally.

It was thought that the hippocampus may "undergo a postnatal sensitive period, during which neuronal activity shows increased responsiveness to environmental stimulation". But after some studies with rats, the results "did not support this hypothesis, however, and instead suggest that, before the emergence of behavioral function, hippocampal cellular activity is insensitive to environmental stimulation."

Research supports the notion of INFANTILE AMNESIA, the lack of memory for experiences that occurred prior to three years of age.

Infantile Amnesia: the inability to remember events from before around 3 ½ years of age

Two possible explanations:
1. Memories were never stored
2. Memories were stored but can’t be retrieved because of either
a. cognitive differences (e.g, language, time, etc.
b. social repression (e.g., freud

Although memories are stored from early infancy, they cannot be easily retrieved.

Early memories are susceptible to interference from later events.

Recent research on one of the body’s “stress-sensitive” systems shows how very stressful experiences also shape a child’s developing brain. When children are faced with physical or emotional stress or trauma, one of these systems “turns on” by releasing the hormone cortisol.

High levels of cortisol can cause brain cells to die and reduces the connections between the cells in certain areas of the brain.

Babies with strong, positive emotional bonds to their caregivers show consistently lower levels of cortisol in their brains. While positive experiences can help brighten a child’s future, negative experiences can do the opposite. Too much cortisol in the brain can make it hard for children to learn and to think. And they may have trouble acting appropriately in stressful situations.

Healthy relationships during the early years help children have healthy relationships throughout life. Deprived of a positive, stimulating environment, a child’s brain suffers. Rich experiences, in other words, really do produce rich brains.

Memories are sensitive to environmental context

Early stimulation sets the stage for how children will learn and interact with others throughout life. A child’s experiences, good or bad, influence the wiring of his brain and the connection in his nervous system. Loving interactions with caring adults strongly stimulate a child’s brain, causing synapses to grow and existing connections to get stronger. Connections that are used become permanent. If a child receives little stimulation early on, the synapses will not develop, and the brain will make fewer connections.

***Recent advances in neuroscience have shown that early experiences also play a fundamental role in brain development. At birth, the human infant brain weighs approximately 350 grams but it more than quadruples its size by the time of adulthood. Most of the neurons that make up the human brain are present at the time of birth; the fourfold change in weight is due primarily to an increase in the connections between the neurons. These connections are established very rapidly during infancy and are contingent, at least in part, upon experience (Greenough, Black, & Wallace, 1987). Although both deprivation and enrichment influence the structure and function of the mammalian brain throughout the lifespan (Black & Greenough, 1998; Winocur, 1998), these experiences may be particularly important early in development when the brain is initially taking shape (Kolb, Forgie, Gibb, Gorny, & Rowntree, 1998; Perry, 1997; Wickelgren, 1999).

Still finding information...more to follow

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