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Old 06-02-12, 01:31 PM
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Re: Memory Training Unlikely to Help in Treating ADHD

Developmental experience: Use-dependent organization of neural systems

In the developing brain, undifferentiated neural systems are critically dependent upon sets of environmental and micro-environmental cues (e.g., neurotransmitters, cellular adhesion molecules, neurohormones, amino acids, ions) to appropriately organize from their undifferentiated, immature forms Appendix 1, Key Points: Brain Development). Lack (or disruption) of these critical cues can result in abnormal neuronal division, migration, differentiation, synaptogenesis -- all of which contribute to malorganization and compromised function in the affected systems (Cragg, 1975; Lauder, 1988; Perry, Wainwright, Won, Hoffman and Heller, 1990b). Two major principles of neurodevelopment related to the timing and nature of these organizing cues are 1) use-dependent development and organization of the brain and 2) critical and sensitive periods.

The brain develops in a sequential and hierarchical fashion -- i.e., from less complex (brainstem) to most complex (limbic, cortical areas). These different areas develop, organize and become fully functional at different times during childhood. At birth, for example, the brainstem areas responsible for regulating cardiovascular and respiratory function must be intact for the infant to survive, and any malfunction is immediately observable. In contrast, the cortical areas responsible for abstract cognition have years before they will be 'needed' or fullyfunctional. This means that there are different times during which different areas of the CNS are organizing and, therefore, either require (critical periods) or are most sensitive to (sensitive periods) organizing experiences (and the neurotrophic cues related to these experiences). Disruptions of experience-dependent neurochemical signals during these periods may lead to major abnormalities or deficits in neurodevelopment -- some of which may not be reversible (see below). Disruption of critical cues can result from 1) lack of sensory experience during critical periods or, more commonly, 2) atypical or abnormal patterns of neuronal activation due to extremes of experience (e.g., child maltreatment).

The simple and unavoidable result of this sequential neurodevelopment is that the organizing, sensitive brain of an infant or young children is more malleable to experience than a mature brain. While experience may alter the behavior of an adult, experience literally provides the organizing framework for an infant and child. Because the brain is most plastic (receptive to environmental input) in early childhood, the child is most vulnerable to variance of experience during this time.
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