Retrograde amnesia

In neurology, retrograde amnesia (RA) is the inability to access memories or information from before an injury or disease occurred.^[1] RA differs from a similar condition called anterograde amnesia (AA), which is the inability to form new memories following injury or disease onset.^[2] Although an individual can have both RA and AA at the same time, RA can also occur on its own; this 'pure' form of RA can be further divided into three types: focal, isolated, and pure RA.^[3] RA negatively affects an individual's episodic, autobiographical, and declarative memory, but they can still form new memories because RA leaves procedural memory intact.^[3] Depending on its severity, RA can result in either temporally graded or more permanent memory loss.^[3] However, memory loss usually follows Ribot's law, which states that individuals are more likely to lose recent memories than older memories.^[4] Diagnosing RA generally requires using an Autobiographical Memory Interview (AMI) and observing brain structure through magnetic resonance imaging (MRI), a computed tomography scan (CT), or electroencephalography (EEG).^[3]^[5]^[6]

Retrograde amnesia

Neurology

(ECT), used as a depression therapy, can cause impairments in memory.^[29] Tests show that information from days and weeks before the ECT can be permanently lost.^[30] The results of this study also show that severity of RA is more extreme in cases of bilateral ECT rather than unilateral ECT. Impairments can also be more intense if ECT is administered repetitively (sine wave simulation) as opposed to a single pulse (brief-pulse stimulation).^[31]

Electroconvulsive therapy

(ECS): The research in this field has been advanced by using animals as subjects.^[32] This is done to further understand RA.

Electroconvulsive shock

Diagnosis[edit]

Since RA affects people's memories to varying degrees, testing is required to fully diagnose RA; these tests, however, are inherently limited if a patient's previous neuropathological medical history is unknown.^[33] As a result, some clinicians diagnose RA by testing patients about factual knowledge, such as current public events.^[33] This testing is limited, however, because people's knowledge about current events differs.^[33] Furthermore, these tests must be adjusted to account for the time period that a patient is alive, which affects the amount of detail included in the questions.^[34] Since some information obtained from this testing is subjective, it is difficult to verify how accurately memories are recalled; this difficulty is especially true for memories from the distant past.^[33]

To avoid these issues, many researchers test for RA using the Autobiographical Memory Interview (AMI).^[33]^[35] The AMI asks patients targeted questions about three different portions of their life: childhood, early adult life, and recent life.^[33] For each period of that individual's life, researchers ask questions that require the patient to use either their autobiographical or semantic memory.^[35] Through the AMI, researchers can better understand the types of memories affected, as well as the degree of a patient's RA.^[33] These AMIs can then be used alongside functional brain imaging techniques like magnetic resonance imaging (MRI), computed tomography scans (CT) and electroencephalography (EEG) that detect brain damage in patients with RA.^[6]

The deals largely with memory consolidation,^[36] where information from the working memory and short-term memory is encoded into long-term storage for future retrieval. Amnesic patients with damage to the hippocampus are able to demonstrate some degree of unimpaired semantic memory, despite a loss of episodic memory, due to spared parahippocampal cortex.^[39] In other words, retrograde amnesics "know" about information or skill, but cannot "remember" how they do.

hippocampus

The and the surrounding areas' role in memory is not well understood. However, this structure appears to be involved in episodic memory recall.^[37]

diencephalon

The are essential for semantic and factual memory processing. Aside from helping to consolidate memory with the hippocampus,^[38] the temporal lobes are extremely important for semantic memory. Damage to this region of the brain can result in the impaired organization and categorization of verbal material, disturbance of language comprehension, and impaired long-term memory. The right frontal lobe is critical for the retrieval of episodic information, while the left frontal region is more active for the retrieval of semantic information.^[40] Lesions in the right hemisphere and right frontal lobes result in the impaired recall of non-verbal material, such as music and drawings.^[41] Difficulties in studying this region of the brain extends to its duties in comprehension, naming objects, verbal memory, and other language functions.^[42]

temporal lobes

The most commonly affected areas are associated with episodic and declarative memory such as the hippocampus,^[36] the diencephalon,^[37] and the temporal lobes.^[38]

Brain plasticity has helped explain the recovery process of brain damage induced retrograde amnesia, where neuro-structures use different neural pathways to avoid the damaged areas while still performing their tasks.^[43] Thus, the brain can learn to be independent of the impaired hippocampus, but only to a certain extent.^[13] For example, older memories are consolidated over time and in various structures of the brain, including Wernicke's area and the neocortex, making retrieval through alternate pathways possible.^[4]

After a head injury, AB had to relearn personal information. Many of AB's habits had also changed.^[48]

[48]

Patient CD reported disorientation of place and time following his injuries as well as relearning previously learned information and activities (e.g., using a razor).

[48]

EF was examined and found to be very confused about social norms (e.g., appropriate attire outside his home). EF exhibited memory loss of his personal experiences (e.g., childhood), and the impaired ability to recognize his wife and parents.

[48]

JG is the first recorded patient with isolated RA.

[10]

GH, a mother and a wife, had surgery in August 2002. When GH woke up after the surgery, she believed it was May 1989. Due to her amnesia, GH experienced great difficulty in her social environment, being overwhelmed by relationships to others.^[48]

[48]

DH, a learning disabilities instructor and husband, sustained a closed head injury. He did not show any normal signs of memory loss but he could not recall anything prior to the accident.

[1]

CDA is a 20-year-old man who fell and experienced head trauma after being unconscious for a little less than an hour. He had a self-identity loss and a retrograde deficit limited to the autobiographical events 5 years before the trauma. He often showed signs of spontaneous speech that was iterative and sometimes incoherent. When he saw his family and friends, he was shocked at how old they looked because he remembered them from 5 years earlier. This case also included amnesia for procedural skills like the fear of shaving or driving, which ultimately was overcome. There were no psychological, neuropsychological, or brain damage problems. His recovery of memory was progressive and spontaneous, where after several months the amnesia was limited to the two years preceding the trauma. This was a classic case of PRA.

[11]

GC was a 38 year old accountant that was found in a town square unable to remember anything about himself and unaware of where he was and how he got there. He was eventually able to recall basic information about himself and his family, but could not recall emotionally charged autobiographical events pertaining to the last 7 years of his life. Within 3–4 days, it was determined that his autobiographical amnesia was clearly and strictly selective for professional events, as he could remember everything that was not related to his job. It was ultimately learned that the job had created severe emotional stress and anxiety due to the extreme hours that triggered a sudden fugue state. He was eventually able to recover most of his memories minus a single work event where he had stolen money from the company. This was a classic case of .^[11]

psychogenic amnesia

AF is a 15-year-old boy who hit his head and lost consciousness. He could not remember anything but was able to play songs on the piano, showing that his procedural memory was still intact. He gradually recovered some memories within the first 2–3 days but had autobiographical amnesia as well as significant memory loss for famous public facts and events for the 2 years prior to the injury.

[11]

L is 19-year-old student who was left with the inability to recall episodic memories after experiencing a in December of 2020. However, he was able to recall things such as his birthday and the street names of Nantes, the city where he resides in. L was part of a case study that associated reduced pupil size as a possible indicator of RA.^[49]

fugue state

Since researchers are interested in examining the effects of disrupted brain areas and conducting experiments for further understanding of an unaffected, normal brain,^[44] many individuals with brain damage have volunteered to undergo countless tests to advance our scientific knowledge of the human brain. For example, Henry Molaison (HM) was someone with significant brain damage and participated in a lot of neurological research. Furthermore, he was also the most tested person in neuropsychology.^[45] All living people who participate are referred to in literature using only their initials to protect privacy.

Each case of RA has led to different symptoms and durations, where some patients have exhibited an inability to describe future plans, whether in the near future (e.g., this afternoon) or in the distant future (e.g., next summer)^[46] because of their inability to consolidate memories.^[13] Furthermore, researchers have also found that some patients can identify themselves and loved ones in photographs, but cannot determine the time or place the photo was taken.^[46] It has also been found that patients with RA greatly differ from the general population in remembering past events.^[47]

A few case examples are:

Although it may seem that people living with brain damage have great difficulty continuing the usual day-to-day aspects, they still can accomplish many feats. People with RA are able to lead a normal life. For instance, KC is a man who has many functional aspects intact; normal intelligence, unaffected perceptual and linguistic skills, short-term memory, social skills, and reasoning abilities.^[46] All of these things are necessary in everyday life and contribute to normal living. KC also is fully capable of scripted activities (e.g., making reservations or changing a flat tire).^[46] In addition, patient HC successfully graduated high school and continued into post-secondary studies,^[47] an obvious accomplishment despite her condition. DH relearned his childhood memories from his parents and can retell the stories, but cannot recall specifics other than what has been told to him.^[1]

Other forms of amnesia[edit]

Other forms of amnesia exist and may be confused with RA. For instance, anterograde amnesia (AA) is the inability to learn new information.^[50] This describes a problem encoding, storing, or retrieving information that can be used in the future.^[51] It is important to note that these two conditions can, and often do both occur in the same patient simultaneously,^[16] but are otherwise separate forms of amnesia.

RA can also be an inherent aspect of other forms of amnesia, namely transient global amnesia (TGA). TGA is the sudden onset of AA and RA caused by a traumatic event, however it is short lived, typically lasting only 4 to 8 hours^[52] TGA is very difficult to study because of the patients' quick recovery.^[53] This form of amnesia, like AA, remains distinct from RA.^[13]

Post-traumatic amnesia (PTA) is a state of confusion that occurs immediately following a traumatic brain injury in which the injured person is disoriented and unable to remember events that occur after the injury.

Psychogenic amnesia, or dissociative amnesia, is a memory disorder characterized by sudden retrograde autobiographical memory loss, said to occur for a period of time ranging from hours to years.

Retrograde amnesia