Long term memories are those that last for years or even decades. Long term memory differs structurally and functionally from short term and working memory. Short term memories move into long term memory via the process of long-term potentiation, the process of strengthening the connections between existing neurons to improve the effectiveness of their communication. Long term memories fade as part of the natural forgetting process, which increases with age, stress and illness. Serious loss of long term memory, however, is the result of either traumatic brain injury or a neurodegenerative disease.

Traumatic brain injury: Depending on what part of the brain has been affected, the ability to remember tastes, smells, appearances, or sounds may be affected. A head injury that causes swelling in the brain reduces the brain's ability to process incoming information. Additionally, once such incoming information is processed and stored in the appropriate area of the brain, the brain may have difficulty retrieving the information when needed. If you suffer from traumatic injury to the head and forget where you had been or what you had been doing for a few days before the accident, you suffer from retrograde amnesia.

Neurodegenerative Disease: the most prevalent neurodegenerative diseases that cause memory loss are Alzheimer’s Disease, Dementia, Huntington’s Disease, Multiple Sclerosis and Parkinson’s Disease. Although none of these conditions act specifically on memory, memory deterioration is a casualty of general cognitive decline.