Memory loss can be partial or total, and it is normal when it comes with aging. Sudden memory loss is usually a result of brain trauma and it may be permanent or temporary. When it is caused by medical conditions such as Alzheimers, the memory loss is gradual and tends to be permanent.

Brain trauma is not the only factor that can cause sudden memory loss. It may appear as a side effect of statin drugs that are used as treatment for those who have hypercholesterolemia. Major causes of sudden loss of memory are strokes. Other causes are long lasting and recurrent illnesses such as meningitis or epilepsy. Either temporary or permanent memory loss can also result from chemical imbalances, exposure to toxic substances, allergies, vitamin deficiencies (such as those caused by alcoholism), or extreme mental illness (Major Depressive Disorder).

Symptoms of memory loss vary from person to person, but can include: forgetting dates and names; beginning a task but then forgetting the purpose of it; getting lost easily; repeating things over and over again, sometimes in the same conversation; and having difficulties performing familiar tasks such as driving or baking. They usually occur gradually and may vary in intensity depending on the cause of the condition.

In psychology, memory is the processes by which information is encoded, stored, and retrieved. Encoding allows information that is from the outside world to reach our senses in the forms of chemical and physical stimuli. In this first stage we must change the information so that we may put the memory into the encoding process. Storage is the second memory stage or process. This entails that we maintain information over periods of time. Finally the third process is retrieval. This is the retrieval of information that we have stored. We must locate it and return it to our consciousness. Some retrieval attempts may be effortless due to the type of information.

From an information processing perspective there are three main stages in the formation and retrieval of memory:

Sensory memory corresponds approximately to the initial 200–500 milliseconds after an item is perceived. The ability to look at an item, and remember what it looked like with just a second of observation, or memorisation, is an example of sensory memory. With very short presentations, participants often report that they seem to "see" more than they can actually report. The first experiments exploring this form of sensory memory were conducted by George Sperling (1963) using the "partial report paradigm". Subjects were presented with a grid of 12 letters, arranged into three rows of four. After a brief presentation, subjects were then played either a high, medium or low tone, cuing them which of the rows to report. Based on these partial report experiments, Sperling was able to show that the capacity of sensory memory was approximately 12 items, but that it degraded very quickly (within a few hundred milliseconds). Because this form of memory degrades so quickly, participants would see the display, but be unable to report all of the items (12 in the "whole report" procedure) before they decayed. This type of memory cannot be prolonged via rehearsal.

Loss may refer to: