Learning and Memory, Neurochemical Aspects
Learning is the process by which the cellular and molecular systems of the brain convert new information into a form that can be permanently stored as a long-term memory. Neurochemical investigations indicate that this process consists of at least two stages: (1) a short-term memory (STM) phase, which is susceptible to physical interference (such as application of an electroconvulsive shock or cooling within seconds or minutes after the acquisition of the information), and (2) a long-term memory (LTM) phase, which is not blocked by such events. The mechanism by which STM is transformed into LTM is called the memory consolidation process. In humans, memories once formed may be stable as long as 50 years. If we search the components of the central nervous system (CNS) looking for molecules that can fulfill this requirement for long-term stability, we find that everything except DNA is in a dynamic state. The average half-life of proteins ranges between 6 and 14 days; ribonucleic acid turnover can vary from a half hour to a day; lipids and carbohydrates are in a rapid state of flux. There is no evidence, as yet, that DNA itself can be modified to encode learning. It seems, therefore, that only the patterns of structure and connectivity of the central nervous system may be sufficiently stable for such a purpose. From such considerations, the search for neurochemical mechanisms of learning and memory reduces to the identification of specific metabolic, physiological, and biochemical parameters that can lead to alterations of neural circuits. Thus, learning and memory formation may be considered as microextensions of the process of neural development.
KeywordsConditioned Stimulus Memory Formation Electroconvulsive Shock ACTH Fragment Memory Consolidation Process
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