Memory is the process that occurs when the brain records and stores information. Memory can be divided into immediate (events that happened in the previous few seconds), intermediate memory (events that happened in the preceding seconds to last few days) and long-term memory (events that happened further back in time). In many cases, when people speak of short-term memory they are referring to immediate and intermediate memory.

Despite this process of recording information, most people forget things from time to time. When this forgetfulness occurs in a consistent pattern or involves impairment that affects a person’s ability to function, they are said to be experiencing memory loss (sometimes referred to as amnesia).

The exact mechanics of memory loss are not completely understood. However, memory loss can occur any time normal functioning of the brain is disrupted. Most often, memory loss is due to disease or physical injury to the brain. The extent of memory loss depends on the type and severity of injury or other cause of the memory loss.

Many areas of the brain are involved in memory storage and retrieval. The temporal lobe and frontal lobe (front part of the brain involved in cognitive function) are primarily responsible for storing and retrieving information. Emotions can also influence memory, which may involve the limbic system (brain structures involved in emotion and motivation, such as the hypothalamus, hippocampus and amygdala). Several large networks of neurons (nerve cells) connect different parts of the brain involved in memory storage and retrieval. Because memory involves so many different areas of the brain, almost any kind of brain damage can cause memory loss.

Short-term memory is stored in the temporal lobe of the brain. This area may be affected in certain degenerative disorders (e.g., Alzheimer’s disease). Long-term memory is stored in both the temporal and parietal lobes of the brain. The parietal lobe may become affected in later stages of some degenerative neurological conditions.

Memory loss is a common symptom of many neurological conditions. It is especially common in people with dementia and people with head injuries. In some cases, memory loss is temporary, lasting from a couple of minutes to several hours before disappearing on its own. However, when memory loss is caused by severe brain damage or certain degenerative neurological conditions, it may be permanent and worsen over time.

The specific cause of a patient’s memory loss will determine whether it is temporary or permanent. For example, a type of memory loss called transient global amnesia is strictly temporary. The cause of a patient’s memory loss will also determine whether the memory loss appears suddenly (as in the case of transient global amnesia) or occurs gradually, over a period of time (e.g., in cases of dementia).  

Memory loss can affect a patient’s ability to remember events of the past, as well as behaviors or skills previously learned. This may impact a patient’s ability to function on a daily basis, depending on the severity and type of memory loss.

Memory loss is often associated with old age. However, it is important to note that mild memory loss associated with aging is not the same as the often severe memory loss associated with medical conditions such as Alzheimer's disease and dementia, which are more prevalent among older adults.