Exceptional memory

The capacity for exceptional memory can take several forms.

Hyperthymesia or hyperthymesitic syndrome is superior autobiographical memory, the type of memory that forms people's life stories. The term thymesia is derived from the Greek word thymesis, meaning "memory".

The capabilities of the affected individuals are not limited to recalling specific events from their personal experience. Hyperthymesia has both enhanced autobiographical and episodic memory There are two important characteristics of hyperthymesia:

Unlike other people with advanced memory abilities, such as savant syndrome (who tend to use calendrical calculation), individuals with hyperthymestic syndrome rely heavily on their personal "mental calendar", which is an automatic and obsessive process. Moreover, individuals with hyperthymesia do not focus on practiced mnemonic strategies. For example, "AJ", who has the first documented case of hyperthymesia, has difficulty consciously applying her memory strategies to help her memorize new knowledge, making her rote memorization abilities below average.

Because it is a recently discovered memory capability, neuroscientific explanations of hyperthymesia are scarce. McGaugh, who coined the term, provides mostly speculation in "A Case of Unusual Autobiographical Remembering". He suggests that "AJ"'s superior autobiographical memory is largely the result of specific impairments rather than enhancements. Her sensitivity to cues that trigger her memories suggest that "AJ" has trouble inhibiting episodic-retrieval mode, which is the neurocognitive state required for present stimuli to be interpreted as memory cues. Because she is unable to "turn off" her retrieval mode, the smallest associations may bring on detailed recollections of "AJ"'s past.

Inhibition in itself is a type of executive functioning, thought to be associated with the right inferior frontal cortex. Although "AJ" is not autistic, McGaugh and colleagues note that she shares some of the executive-functioning deficits that occur with autism. These deficits, along with anomalous lateralization and "AJ"'s obsessive–compulsive tendencies, point to a neurodevelopmental frontostriatal disorder common in autism, OCD, ADHD, Tourette's syndrome, and schizophrenia. The frontostriatal system is made up of the dorsolateral prefrontal cortex, lateral orbitofrontal cortex, cingulate, supplementary motor area, and associated basal ganglia structures.

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