Nancy Huang

Sep 12th 2022

Amnesia in the Brain: What Goes Wrong?


Humans need to remember a huge assortment of information and experiences to be reasonably self-sufficient. While everyone forgets things occasionally, some people experience a severe form of memory loss called amnesia. While it’s normal to occasionally forget where you parked your car, forgetting that you have a car might be a sign of amnesia in the brain.

What Causes Amnesia?

Amnesia can be the result of brain injury or damage, according to the Mayo Clinic. Causes may include:

  • A blow to the head
  • Brain inflammation due to infection
  • Lack of oxygen due to a stroke or heart attack
  • Seizures
  • Brain tumors
  • Brain surgery
  • Degenerative brain diseases such as Alzheimer’s

Depending on the severity of the brain injury, amnesia may be temporary or permanent. It may improve as the brain heals or may become progressively worse as conditions deteriorate.

Heavy alcohol users can develop alcoholic amnesia, which affects 1% to 3% of the population, according to the Cleveland Clinic. Researchers believe that alcohol prevents the body from processing vitamin B1, which is essential to memory formation. Brain damage from alcoholic amnesia is permanent in 80% of cases and can severely inhibit the ability to form new memories.

What Are the Different Types of Amnesia?

Anterograde amnesia is characterized by difficulty learning new information and forming new memories, and it’s the most common form of amnesia in the brain. Retrograde amnesia involves difficulty recalling previously familiar information, including personal experiences and facts. Retrograde amnesia typically affects recent memories (the name of the neighbor that moved in last year) more than earlier memories (the name of your second-grade teacher). Older memories are stronger because they’ve been repeatedly reinforced over time.

Post-traumatic amnesia occurs immediately after a significant head injury (e.g., from a car accident or sports injury) and can include trouble forming new memories, recalling old memories or both. Post-traumatic amnesia is usually temporary —lasting hours, days or weeks. As the brain recovers, lost memories may again become accessible. However, it’s common for memories immediately surrounding the event to be “erased” since the brain didn’t have time to form strong memories.

Psychogenic amnesia can occur after experiencing significant emotional trauma, such as a violent crime. This usually involves an inability to remember past information surrounding the traumatic event but can be so severe that the person temporarily forgets their own identity.

What Part of the Brain Is Affected by Amnesia?

Much of what we know about amnesia started with Henry Gustav Molaison, more commonly known as patient H.M. According to The New York Times, Molaison suffered from epileptic seizures that didn’t respond adequately to medication. At the age of 27, he underwent surgery to remove the brain areas thought to be responsible for his seizures — portions of the medial temporal lobes (MTLs) including the hippocampus. The year was 1953 and the surgery was very much experimental.

The surgery reduced Molaison’s seizures but also caused severe anterograde amnesia. He was unable to remember new information for the next 55 years, until his passing in 2008. During that time, he graciously agreed to participate in thousands of memory tests, despite forgetting the researcher as soon as they walked out the door. Because of Molaison’s generosity, we now know that damage to the hippocampus results in severe deficits in verbal learning and recall. Molaison’s short-term memory (which usually lasts five to 20 seconds) was found to be largely intact. He could recall a list of words immediately after they were presented. But after a few minutes, he could no longer recall the words or remember that a list had been presented. Molaison’s other types of memory were found to be intact, even if he wasn’t consciously aware of developing new memories.

It’s now believed that new memories depend on the hippocampus and are then forgotten or fully integrated with preexisting memories that are stored in other parts of the brain. Studies with other amnesia patients have helped determine what part of the brain is affected by amnesia.

How Is Amnesia Diagnosed and Treated?

To diagnose amnesia, health care providers may first assess memory through a conversation with the patient and observe how well they can recall past information. To identify a possible cause, doctors may order blood tests to check levels of vitamin B1, B12 and thyroid hormones. An MRI or CT scan can identify signs of a brain tumor or stroke. An EEG (electroencephalogram) can check for seizure activity, and a spinal tap may detect brain infections.

There’s no medication specifically for amnesia. Treatment typically focuses on the underlying physical or mental disorder: concussion, brain tumor, cardiovascular disease, emotional trauma, alcohol abuse, etc. For some conditions, amnesia may improve as the brain heals. In other cases, the focus is on slowing the decline. Psychotherapy or cognitive rehabilitation may help. Support from family and friends is essential. Patients may benefit from seeing photographs of past events, smelling and tasting favorite foods, and hearing familiar music.

With persistent memory loss, patients may be able to compensate through organizational strategies, such as using a whiteboard or cellphone to keep track of essential information, appointments, etc. If memory loss is severe, patients will likely need help with daily life tasks.

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