The term memory refers to a person's ability to retain and recall information. In order to retain memory, chemical reactions must take place within the brain.

Hundreds of neurotransmitters (chemicals in the brain) are emitted and carry information to appropriate areas of the brain for consequent storage as memory. Long-term memory is stored when a group of neurons connect together.

Memories are formed via a process called encoding, which may occur in several parts of the brain. Encoding allows a specific meaning to be allocated to units of information.

In order for encoding to occur attention must be paid to the information to be encoded. As we sense stimuli messages are sent to the brain via nerves. These messages are held for a short period of time as sensory memory.

The type and amount of attention paid to information will affect the effectiveness of the encoding process. There are three different types of encoding:

1) Structural encoding: this type of encoding is based on attention paid to physical characteristics of the stimulus or information. Coding occurs at a shallow level.

2) Phonemic encoding: Encoding is based on the sounds of words. Coding occurs at an intermediate level.

3) Semantic encoding: Encoding is based on the meaning of information and occurs at a deep level.

If insufficient attention is not paid to the information (if attention is less than eight uninterrupted seconds) encoding will not take place.

Encoding can be enhanced via increasing the amount and type of stimuli (i.e. combining visual stimuli with verbal stimuli) or by making information relevant on a personal level.

After encoding memory is consequently stored. The type of storage depends on the type of memory, whether it be short term, long term or sensory memory. The types of memory are further discussed in chapter 2.

When an individual recalls a memory, this process is known as retrieval. In some circumstances retrieval may fail, resulting in the inability to remember.

Reasons for failure during the retrieval stage of memory are discussed in chapter 3. Certain factors may help increase chances of retrieval including cues and re-enactment of the emotional state present during encoding.

There are many theories on the way in which memory works, however there is no theory that is universally agreed upon. Some of the more common theories are as follows:

1)              Videotape theory: This theory proposes that the mind records all details during a lifetime, and that retrieval is simply a matter of searching for the relevant episode and consequently the scene of interest.

2)              Reconstructive theory: This theory proposes that information is either not remembered or is not remembered in full, in which case the mind will invent a memory based on previous experience, if retrieval is required.

3)              Distribution theory: It has been proposed that mind is distributed evenly throughout the body and each area is able to retain memory. This is indicated through the body's ability to automatically perform certain daily procedures.

4)              Selective retention theory: It is believed that a mechanism capable of repressing or dissociating memories subconsciously exists. After this mechanism comes into play memories may only be retrieved via the implementation of memory therapy.

5)              Constructive theory: It is hypothesis that the individual will invent memories based on current situations, needs and desires.

6)              Neural Circuit theory: This theory suggests that specific circuits in the brain exist for specific memories. Different circuits are accessed according to the type of information the individual is required to access.       

Despite the many models of human memory there is no theory that is universally agreed on and thus no definitive answer on how memory actually works.