MemoryThis article is about the human memory. For memory as a storage-device, see computer memory
Memory is one of the activities of the human mind, much studied by cognitive psychology. It is the capacity to retain an impression of past experiences. There are multiple types of classifications for memory based on duration, nature and retrieval of perceived items. The main stages in the formation and retrieval of memory, from an information processing perspective, are:
When we are given a seven digit number, we can remember it only for a few seconds and then forget (short term memory). On the other hand we remember our telephone numbers, since we have stored it in our brain after long periods of consolidation (long term memory). The definition of working memory, which is erroneously used as a synonym of short-term memory, is based on not only the duration of memory retention but also the way how it is used in daily life activities. For instance, when we are asked to multiply 45 with 4 in our head, we have to perform a series of simple calculations (addition and multiplications) to give the final answer. The process of keeping in mind all these informations for a short period of time is called working memory. Another good example is a chess player, who is playing with multiple opponents at the same time and trying to remember the positions of pieces in all games and using this information to make a good move, when required. Long-term memory can further be classified as declarative (explicit) and procedural (implicit). Explicit memory requires conscious recall, in other words the information must be called back consciously when it is required. If this information is about our own lives (what we ate for breakfast in this morning, our birth date etc.), it is called episodic memory, if it concerns our knowledge about the world (capital of France, presidents of US etc.), then it is called semantic memory. Implicit memory is not based on the conscious recall of information stored in our brain, but on the habituation or sensitization of learned facts. We perform better in a given task each time we repeat the task, that is we use our implicit memory without necessarily remembering the previous experiences but using the previously learned behaviours unconsciously.
The fields of neurophysiology and biochemistry have made some advances in the understanding of memory.
Critical locations for memory are amygdala, hippocampus, fornix, mammillary bodies, thalamus, hypothalamus as well as the cerebral cortex
Complementary encoding theory stipulates that some circuits (e.g. the hippocampus) are used for fast and specific encoding, while generalized overlapping representations are stored in the neocortex.
Many researchers believe that encoding of long lasting neocortical memories occurs during sleep.
Recent advances in neural network research make it possible to understand memory consolidation and retrieval in a computational sense.
A hypothesized celluar basis of memory and learning, for which there is some evidence, involves strengthening of the synapses that link nerve cells (or neurons).
This is known as the Hebbian theory, after the Canadian neuropsychologist Donald O. Hebb.
It has been asserted that GABA signals interfere with the registration and consolidation stages of memory formation.
As the GABA system is found in the hippocampus, which is thought to play a large role in memory formation, this is thought to be possible.
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