Highly Superior Autobiographical Memory

Highly Superior Autobiographical Memory (HSAM) is the ability to retain a large capacity of vivid and accurate personal events. In 2006, hyperthymesic syndrome was coined to describe a condition where individuals automatically remember past autobiographical experiences triggered by a location, event or person[1]. Individuals diagnosed with hyperthymesia are able to account his or her past in extreme detail, allowing them to recall memories such as events that had occurred, the clothes people wore and the conversations that were held[2]. In contrast to the typical forgetting curve of daily events, individuals with hyperthymesia have the ability to remember past histories of their day-to-day lives for long periods of time. This phenomenon is a type of Exceptional Memory.

60 Minutes[16]
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Individuals with HSAM

1 General Phenomenon

1.1 AJ

60 Minutes
Dr. McGaugh discussing Louise Owen's superior autobiographical memory

Although hyperthymesia is a recently discovered condition, there are a significant number of cases outlining this phenomenon. AJ is one of the precedent case studies investigating hyperthymesia. AJ approached Parker, Cahill & McGaugh[3], reporting that she experiences severe disturbances in her everyday life due to her uncontrollable autobiographical memory. Upon testing, the researchers discovered that her recollection of personal memories were continuous, immediate and uncontrollable. In addition, they found that AJ possessed a large memory capacity specific to her autobiographical experiences. Although AJ does not have a family history of with hyperthymesia, AJ can recall precise events everyday starting from 14 years of age to the current time. She reports having a mental calendar that can re-generate any experiences on a selected day. Despite her ability to accurately recall a large number of experiences, AJ was unable to transfer her superior memory skills to personally irrelevant information. For example, AJ was able to recall events that occurred on a chosen date upon recall. However, she was unable to remember large streams of numbers. In addition, AJ possessed poor skills in tasks requiring mnemonic strategies or rote memorization. The patient reported that her memory was automatic rather than strategic and that most of her memory appears without conscious effort. Due to her difficulty inhibiting her recollection of the past, she spends the majority of her time re-living each memory.

“I think about the past all the time… It’s like a running movie that never stops. It’s like a split screen. I’ll be talking to someone and seeing something else… Like we’re sitting here talking and I’m talking to you and in my head I’m thinking about something that happened to me in December 1982, December 17, 1982, it was a Friday, I started to work at a Gs (a store)…”[3]

Over the past few years, hyperthymesia became a topic of interest and began to popularize. Since then, more cases of individuals with superior autobiographical memory have been identified. In 2010, CBS aired "a special about this phenomenon on 60 Minutes, speaking to individuals with hyperthymesia about their condition[2].

2 Current Understanding

2.1 Childhood Amnesia

Freud was the first to begin preliminary studies of autobiographical memories. Coining the term “childhood amnesia”, Freud observed that humans had low recollection of their experiences as an infant and in early childhood[4]. Researchers identified that childhood amnesia is a period of time for the growth and maturation of neurons developing the use of language, self-concepts and autobiographical memories beginning at the age of 2. However, recent research indicates that individuals tend to lose memories of events that occur before the age of 3 and retain vague outlines of their lives before the age of 7[5]. By the age of 5, children tend to remember roughly 63% of their memories, ultimately receding to 35% by age 8. With hyperthymesia as a young field, it is still unclear whether there are different neural circuits operating that may allow selected individuals to retain their earliest memories.

2.2 Environment

As an alternative explanation, researchers postulated that the quality of an individuals’ childhood environment might contribute to the development of superior autobiographical memory. Diamond, Krech & Rosenzweig[7] believed that an enriched environment supports the growth of one’s memory. These researchers hypothesized that populations living in an impoverished area have restricted accessibility to resources such as toys that cultivates the development of glial cells, enhancing the growth rate of cortical areas. A healthy and rich environment will increase the likelihood of an individual to fully develop their cortices, maturing their cognitive processing. In contrast, individuals experiencing a reduction in cortical surface area may result to poor memory abilities, due to the absence of neurons to establish and support efficient communication between cortical regions. This notion is similar to the neurological changes within young musicians. After practicing for a long period of time, the cortical area representing muscles involved in playing their instrument will be greater than non-musically inclined people. However, the researchers’ proposal does not clarify specific differences within a childhood environment that will cultivate neuronal growth and help develop superior memory skills.

3 Neural Mechanisms

3.1 Increase in Cortical Area

Enlarged cortical surface area is one of the first differences identified among individuals with superior autobiographical memory[6]. Anterior and medial parts of the brain are identified to have an increase in white matter. It is postulated that increases in surface area enhances information transmission within the cortex as the connectivity between neurons are also strengthened.

3.2 Hyperactive Amygdala

Researchers indicate a hyperactive amygdala may significantly contribute to superior autobiographical memory recall[8]. Increased activity in the amygdala may enhance self-referential information processing by associating relevant information with strong emotions. Information relevant to the self is processed with greater priority and detail than other daily engrams. Brandon, Hussey & Donahue[9] discovered an individual with hyperthymesia had a 20% enlarged right amygdala. In addition, the case study is capable of accurately recalling memories from the age 9. Complementing the amygdala’s hyper-activation, the visual cortex is also active to enrich details of encoded memory.

3.3 Hippocampus and the Prefrontal Cortex

The Prefrontal Cortex[15]
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The hippocampus may also play a significant role in the retrieval of autobiographical memories. Supporting the memory consolidation theory, Cabeza & St Jacques[10] identified the left hippocampus to be active during recollection of recent and remote autobiographical memories. In addition, they found prefrontal regions were involved during self-referential and memory search processing. The left lateral PFC aided in efficient memory search processes while interacting with the medial PFC that is responsible for retrieving specific memories. The researchers found that greater autobiographical memory retrieval correlated with less inhibition from the medial PFC. Enhanced activation of the hippocampus, interactions between the lateral PFC and medial PFC as well as a significantly reduced inhibition of the medial PFC are factors that may be underlying mechanisms for hyperthymesia.

3.4 Self-Memory System

Conway & Pleydel-Pearce[12] proposed that individuals contain a self-memory system (SMS). The SMS contains autobiographical knowledge and current goals of the current self. When SMS is active, it helps associate cues with specific autobiographical memory for efficient encoding and retrieving purposes. There are three types of information that is stored for autobiographical memory: lifetime periods, general events and event-specific knowledge. Lifetime periods include milestone life events such as going to school for the first time or attending university. General events are single representations of repeated events such as your daily routine every morning. Lastly, event-specific knowledge refers to individual events that are memorable for its unique details and occurrence. It is proposed that encoding each type of memory requires continuous association of cues to specific autobiographical memory traces. In this aspect, greater specificity of cues for each memory may enable individuals to evoke experiences more efficiently.

In contrast, Martinelli, Pserduti & Piolino[13] hypothesized a revised system responsible for constructing and retaining autobiographical memory. These researchers believe that memory of the self can be categorized under two aspects: episodic and semantic autobiographical memory. The episodic memory contributes to maintaining vivid aspects of the memory whereas semantic memory consists of knowledge about one’s own life and personal identity. The researchers concluded that moving from posterior to anterior cerebral regions is correlated with increased abstraction ideologies of the self. In addition, episodic autobiographical memory was responsible for activating posterior and the hippocampus. While episodic and semantic memory of one’s life predominantly activates rostral areas of the brain, conceptual information about the self resides in the activation of medial prefrontal regions. Their research indicates that autobiographical information is stored within multiple dimensions rather than one coherent engram. Therefore, their discovery provides insight on whether individuals with hyperthymesia may have above average activation levels in these regions during their autobiographical recollection.

3.4.1 Delayed Self-Recognition

Although there are hypothesized autobiographical systems accounting for the storage of self-relevant knowledge and experiences, individuals must have mature cognitive abilities to segregate themselves from the environment. This phenomenon is known as the self-recognition process. A potential explanation for hyperthymesia is an earlier onset of self-recognition, allowing these individuals to be aware that their experiences are unique and personal, enhancing their encoding for these self-relevant memories[12]

3.5 OCD Debate

In the past few years, there has been a debate on the similarity between individuals with hyperthymesia and Obsessive Compulsive Disorder (OCD) patients. Recent research has overlapped similar increases in brain densities of the prefrontal cortex and hippocampus. A few researchers have proposed that individuals with OCD may be involved with active recall of their past memories. However, countering studies investigating the potential for hyperthymesia to be a symptom of OCD claim that memories of OCD patients are often disrupted by the presence of other cognitive illusions[14]. Furthermore, measurement for vivid past autobiographical experiences was difficult due to the co-morbidity of major depression, leading to poor recollection of all memories.

Bibliography
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