memory

Memory

Is an informational processing system by which information is stored, and recalled. Without memory, we could not remember past events, we could not learn language.
There are three main stages in the information processing and formation of memory:
Encoding or registration: receiving, processing the information
Storage: creation of a permanent record of the information in short term or long term memory
Retrieval, recall: calling back the stored information
Our brain receives millions of sensory information .If our minds attempted to remember all this information, the memory capacity of the brain would be exceeded within minutes. Fortunately, the brain has the ability to learn to ignore information that is of no consequence. This results from inhibition of the synaptic pathways for this type of information; the resulting effect is called habituation. This is a type of negative memory.
Conversely,for incoming information that causes important consequences such as pain or pleasure, the brain is storing them. It results from facilitation of the synaptic pathways, and the process is called memory sensitization. This is positive memory
special areas in the limbic regions of the brain determine whether information is important or unimportant and make the decision whether to store or to ignore the information (99% of the information usually ignored and only 1% is stored ).
Habituation and facilitation
There are two synaptic terminals. One terminal is from a sensory input neuron and terminates directly on the surface of the neuron that is to be stimulated; this is called the sensory terminal. The other terminal is a presynaptic ending that lies on the surface of the sensory terminal, and it is called the facilitator terminal. When the sensory terminal is stimulated repeatedly but without stimulation of the facilitator terminal, signal transmission at first is great, but it becomes less and less intense until transmission is ceases. This phenomenon is habituation. It is a type of negative memory for events that are insignificant.
Conversely, if a noxious stimulus excites the facilitator terminal at the same time that the sensory terminal is stimulated, the transmission becomes stronger and stronger; and it will remain strong for
minutes, hours, days, or, weeks.This phenomenon is facilitation. for positive memory
Classification of Memories:
classification of memories into
(1) short-term memory (STM), which includes memories that last for seconds or minutes unless they are converted into longe-term memories
Capacity of short-term memory is limited
Duration of short-term memory is brief
Without attention and repetition, or association with important events, information is lost rapidly from STM
(2) intermediate long-term memories, which last for days to weeks but then fade away
(3) long-term memory, which, once stored, can be recalled up to years or even a lifetime later.
Structural Changes Occur in Synapses During the Development of Long-Term Memory:
1. Increase in number of transmitter vesicles released
2. Increase in vesicle release sites for secretion of transmitter substance.
3. Increase in number of presynaptic terminals.
Thus, the structural capability of synapses to transmit signals appears to increase during establishment of true long-term memory.


Memories are frequently classified according to the type of information that is stored as follows:
1. Declarative memory basically means memory of facts and events. Its type of long-term memory.
2. Skill memory is frequently associated with motor activities of the person’s body, skills learned by practice.
Its HYPERLINK "https://en.wikipedia.org/wiki/Long-term_memory" \o "Long-term memory" long-term memory which aids the performance of particular types of tasks without conscious control or attention such as all the skills developed for hitting a tennis ball .
Another type of memory, called “working memory,” that includes mainly short-term memory located in prefrontal areas, that is used during the course of intellectual reasoning but is terminated when the problem is resolved.
By combining all these temporary bits of working memory, we have the abilities to (1) prognosticate; (2) plan for the future; (3) delay action in response to incoming sensory signals until the best course of response is decided.

Consolidation of Memory

For short-term memory to be converted into long-term memory that can be recalled weeks or years later, it must become “consolidated.” That is, the short-term memory if activated repeatedly will initiate chemical, physical, and anatomical changes in the synapses that are responsible for the long-term type of memory.
repetetion of the same information again and again in the mind accelerates and potentiates the degree of transfer of short-term memory into long term memory and therefore accelerates and enhances consolidation.
during consolidation, the new memories are not stored randomly in the brain but are stored in direct association with other memories of the same type. This is necessary if one is to be able to “search” the memory store at a later date to find the required information.

Role of Specific Parts of the Brain in the Memory Process

Hippocampus Promotes Storage of Memories
It is involved in many declarative memory functions
Damage of hippocampus cause patients are unable to establish new long-term memories called anterograde amnesia ( inability to recall the recent past),while long-term memories from before the event remain intact (old, established memories).

Damage in some thalamic areas may lead to retrograde amnesia When retrograde amnesia occurs, where memories created prior to the event are lost while new memories can still be created.
In some people who have hippocampal lesions, some degree of retrograde amnesia occurs along with anterograde amnesia.
Combination of anterograde and retrograde amnesia, sometimes called global amnesia.