Understanding retrograde amnesia, a symptom of hippocampus damage: Causes, symptoms, types, and treatment

Retrograde amnesia is a disorder that affects an individual’s ability to remember incidents or experiences preceding a specific event in time. This means you are able to make new memories but are unable to recall your past.

Retrograde amnesia is marked by an impairment of autobiographical memory. This is the exact opposite of anterograde amnesia, which refers to the inability for an individual to make new memories.

What causes retrograde amnesia?

The causes of retrograde amnesia are not completely understood, but it is thought to be the result of traumatic brain damage. The following are various pathological events and regions of the brain involved in memory formation:

• Hippocampus: A region of the brain that plays an important role in encoding and storing both short-term and long-term memories.
• Diencephalon: A part of the brain that transmits sensory information to the cerebral hemisphere and to control functions of the peripheral nervous system.
• Temporal lobes: A part of the cerebral cortex, this region is responsible for speech and hearing memory. This part of the brain is also involved in high level visual and memory processing.
• Traumatic injuries: This is the most common cause of retrograde amnesia in which injuries occur to the brain. External forces caused by a hard blow to the head can lead to diffuse axonal injury—tearing of nerve fibers and subsequent formation of extensive lesions. The extent of the injury is often dependent on the impact of the external force and location of the injury.
• Psychologically disturbing events: Not all cases of retrograde amnesia occur after an injury. They may, in fact, be the result of a traumatic event. Regular episodes of metal stress and emotion fear can be a trigger for the onset of retrograde amnesia.
• Korsakoff syndrome: This is a disorder commonly seen in alcoholic patients as they are commonly malnourished. A depletion of vitamin B1 or thiamine in the brain leads to Korsakoff syndrome. Symptoms of this condition include retrograde amnesia and are often exacerbated by the neurotoxic effects of alcohol.
• Infectious conditions: Becoming infected by malicious bacteria or viruses can lead to them affecting the brain. They may invade the spinal cord and surrounding structures eventually reaching the brain leading to symptoms. Many infectious disorders may lead to retrograde amnesia. These include meningitis, myelitis, encephalitis, and brain abscesses.
• Surgery: All surgeries pose some risk to the patient, especially brain surgery. In an attempt to cure an existing brain disorder, surgeons often remove the hippocampus and temporal lobes that lead to memory loss.
• Chronic alcohol abuse: Alcohol can exhibit many neurotoxic effects on the brain, leading to conditions such as Korsakoff syndrome.

Symptoms of retrograde amnesia

The common trait of retrograde amnesia is not remembering past events. Not all past things are forgotten, however, as the memory of meanings (declarative memory) that aids in understanding other factual information is often retained. Other symptoms that can be appreciated include:

• Improper organization and categorization of verbal material
• Long-term memory loss
• Unplanned travel or wandering from home or workplace
• Incorrect way of language formation
• Difficulty recollecting non-verbal information

Types of retrograde amnesia

• Extreme retrograde amnesia: This is when a person suffers from permanent memory loss to the extent of forgetting who they are. However, memory loss can be selective or categorized.
• Temporally graded retrograde amnesia: A short-term impairment in retrieving memory. Traces of anterograde amnesia may be present.
• Pure retrograde amnesia: Having no trace of anterograde amnesia. This form is considered particularly rare.=
• Focal retrograde amnesia: Having traits of anterograde amnesia. It has more psychological abnormalities rather than physical abnormalities. This particular type is characterized by mild forms of both anterograde and retrograde amnesia.
• Isolated retrograde amnesia: An extreme form of retrograde amnesia and linked to a visible thalamic lesion of the brain. This form is characterized by an extreme inability to recall past events

Diagnosing and treating retrograde amnesia

Unfortunately, there is no one single test to diagnosis retrograde amnesia, instead, it is considered a clinical diagnosis though the documentation of various clues and ruling out other potential causes for symptoms. Testing for factual knowledge of autobiographical memory though an interview is often done. Assessment of broad time lines is often investigated, testing knowledge of childhood, early adult life, and recent facts. If a person were to present with the condition, the attending physician may perform the following in order to reach a diagnosis.

• Physical exam: Consists of a neurological exam which tests reflexes, muscle tone, muscle strength, sensory function, gait, posture, coordination, and balance. Question regarding thinking, judgment, and memory may also be asked.
• Brain and imaging tests: These are primarily looking for any pathology that may be causing the memory loss. Looking at the structure of the brain may give clue to a potential stroke event or a tumor growth can be easily observed via computerized tomography (CT) or magnetic resonance imaging (MRI). An electroencephalogram (EEG) may also be used looking for seizure activity.

The is no specific treatment available for retrograde amnesia, instead finding an individual particular underlying cause will often dictate the course of therapy

Minimizing additional damage to the brain is often implemented and come in the form of a diuretic, anti-seizure drugs, and surgical resection. The use of antibiotic, steroids and anticonvulsants can help control and eradicate the spread of bacterial infection in the brain.

In cases where chronic alcoholism is the cause of amnesia symptoms, counseling and education about their disease are recommended. Treatment the resultant malnutrition and assuring adequate amounts of thiamine are taken will also help prevent the cause of amnesia.

During ongoing cases, in which an individual is currently suffering from the condition, all one can do is support the individual. Scheduling regular counseling sessions with a neurologist can help bring back memories.

Related: Transient global amnesia: Causes, symptoms, and treatment