The storage of memory can be divided into three stages: working, short-term, and long-term. Long-term memories can also be sub-divided based on the type of the memory: those dealing with facts (declarative) and those dealing with skills (procedural).
The brain briefly stores information required for the immedi-ate performance of a task. This task-associated memory is called working memory. It lasts only a few seconds to minutes and occursmostly in the frontal cortex. Working memory is limited primarily by the number of bits of information (about seven) that can be stored at any one time. When new information is presented, old information, previously stored in working memory, is eliminated. What happens to a telephone number you just looked up if you are distracted?
Short-term memory lasts longer than working memory and can be retained for a few minutes to a few days. Short-term memo- ries are stored by a mechanism involving increased synaptic trans- mission. Short-term memory is susceptible to brain trauma, such as physical injury or decreased oxygen, and to certain drugs that affect neural function, such as general anesthetics.
Short-term memory is transferred to long-term memory, where it may be stored for only a few minutes or become per manent, by consolidation, a gradual process involving the for- mation of new and stronger synaptic connections. The length of time memory is stored may depend on how often it is retrieved and used. Declarative memory, or explicit memory, involves the retention of facts, such as names, dates, and places, as well as related emotional undertones. Emotion and mood apparently serve as gates in the brain and determine what is stored in long-term declarative memory. Procedural memory, or reflexive memory,involves the development of motor skills, such as riding a bicycle. Only a small amount of procedural memory is lost over time.
Long-term memory involves structural and functional changes in neurons that lead to long-term enhancement of synaptic trans-mission. A whole series of neurons, called memory engrams, or memory traces, are probably involved in the long-term retentionof a given piece of information, a thought, or an idea. Repeating the information and associating it with existing memories help us transfer information from short-term to long-term memory.