The two main features of amnesia are:
- Impaired ability to learn new information following the onset of amnesia (anterograde amnesia)
- Impaired ability to recall past events and previously familiar information (retrograde amnesia)
Most people with amnesia have problems with short-term memory — they can't retain new information. Recent memories are most likely to be lost, while more remote or deeply ingrained memories may be spared. Someone may recall experiences from childhood or know the names of past presidents, but not be able to name the current president or remember what month it is or what was for breakfast.
Isolated memory loss doesn't affect a person's intelligence, general knowledge, awareness, attention span, judgment, personality or identity. People with amnesia usually can understand written and spoken words and can learn skills such as bike riding or piano playing. They may understand they have a memory disorder.
Amnesia isn't the same as dementia. Dementia often includes memory loss, but it also involves other significant cognitive problems that lead to a decline in the ability to carry out daily activities.
A pattern of forgetfulness is also a common symptom of mild cognitive impairment (MCI), but the memory and other cognitive problems in MCI aren't as severe as those experienced in dementia.
Additional signs and symptoms
Depending on the cause of the amnesia, other signs and symptoms may include:
- False recollections (confabulation), either completely invented or made up of genuine memories misplaced in time
- Confusion or disorientation
When to see a doctor
Anyone who experiences unexplained memory loss, head injury, confusion or disorientation requires immediate medical attention.
A person with amnesia may not be able to identify his or her location or have the presence of mind to seek medical care. If someone you know has symptoms of amnesia, help the person get medical attention.
Normal memory function involves many parts of the brain, and any disease or injury that affects the brain can interfere with the intricacies of memory.
Amnesia can result from damage to brain structures that form the limbic system, which controls your emotions and memories. These structures include the thalamus, which lies deep within the center of your brain, and the hippocampal formations, which are situated within the temporal lobes of your brain.
Amnesia caused by brain injury or damage is known as neurological amnesia. Possible causes of neurological amnesia include:
- Brain inflammation (encephalitis) as a result of infection with a virus such as herpes simplex virus, as an autoimmune reaction to cancer somewhere else in the body (paraneoplastic limbic encephalitis), or as an autoimmune reaction in the absence of cancer
- Lack of adequate oxygen in the brain, for example, from heart attack, respiratory distress or carbon monoxide poisoning
- Long-term alcohol abuse leading to thiamin (vitamin B-1) deficiency (Wernicke-Korsakoff syndrome)
- Tumors in areas of the brain that control memory
- Degenerative brain diseases, such as Alzheimer's disease and other forms of dementia
- Certain medications, such as benzodiazepines
Head injuries that cause a concussion, whether from a car accident or sports, can lead to confusion and problems remembering new information. This is especially common in the early stages of recovery. But head injuries usually don't cause severe amnesia.
Another rare type of amnesia, called dissociative (psychogenic) amnesia, stems from emotional shock or trauma, such as being the victim of a violent crime. In this disorder, a person may lose personal memories and autobiographical information, but usually only briefly.
The chance of developing amnesia might increase if you've experienced:
- Brain surgery, head injury or trauma
- Alcohol abuse
Amnesia varies in severity and scope, but even mild amnesia takes a toll on daily activities and quality of life. The syndrome can cause problems at work, at school and in social settings.
It may not be possible to recover lost memories. Some people with severe memory problems need to live in a supervised situation or extended-care facility.
Because damage to the brain can be a root cause of amnesia, it's important to take steps to minimize your chance of a brain injury. For example:
- Avoid excessive alcohol use.
- Wear a helmet when bicycling and a seat belt when driving.
- Treat any infection quickly so that it doesn't have a chance to spread to the brain.
- Seek immediate medical treatment if you have any symptoms that suggest a stroke or brain aneurysm, such as a severe headache or one-sided numbness or paralysis.