Congenital defect of the brain or spinal cord from abnormal growth of their precursor, the neural tube (see embryology), usually with spine or skull defects. The tube may fail to close properly, have parts missing, or have a blockage (see hydrocephalus). In spina bifida, vertebrae are open over the back of the spinal cord, usually at the base. This may not affect function if no further defects (local absence of skin or meninges, protrusion of tissue, defect opening into the spinal cord) exist. The more serious forms can cause paralysis and impair bladder and bowel function. In encephalocele, a meningeal sac containing brain tissue protrudes from the skull. The effects depend on the amount of tissue involved. Adequate folic-acid intake by women of childbearing age reduces the risk of neural tube defects. Early surgery can prevent or minimize disability.
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Capacity of neurons and neural networks in the brain to change their connections and behaviour in response to new information, sensory stimulation, development, damage, or dysfunction. Rapid change or reorganization of the brain's cellular or neural networks can take place in many different forms and under many different circumstances. Neuroplasticity occurs when neurons in the brain sprout and form synapses. As the brain processes sensory information, frequently used synapses are strengthened while unused synapses weaken. Eventually, unused synapses are eliminated completely in a process known as synaptic pruning, which leaves behind efficient networks of neural connections. Neuroplasticity occurs during development in childhood, following physical injury such as loss of a limb or sense organ, and during reinforcement of sensory information such as in learning. Neuroplasticity forms the basis of research into brain-computer interface technology, in which computers are designed to interact with the brain to restore sensation in people with an impaired sense such as the loss of vision. Research on neuroplasticity is also aimed at improving scientists' understanding of how to reactivate or deactivate damaged areas of the brain in people affected by stroke, emotional disorders, chronic pain, psychopathy, or social phobia; such research may lead to improved treatments for these conditions.
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Type of parallel computation in which computing elements are modeled on the network of neurons that constitute animal nervous systems. This model, intended to simulate the way the brain processes information, enables the computer to “learn” to a certain degree. A neural network typically consists of a number of interconnected processors, or nodes. Each handles a designated sphere of knowledge, and has several inputs and one output to the network. Based on the inputs it gets, a node can “learn” about the relationships between sets of data, sometimes using the principles of fuzzy logic. For example, a backgammon program can store and grade results from moves in a game; in the next game, it can play a move based on its stored result and can regrade the stored result if the move is unsuccessful. Neural networks have been used in pattern recognition, speech analysis, oil exploration, weather prediction, and the modeling of thinking and consciousness.
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