Lacunar amnesia
Lacunar amnesia is the loss of memory about one specific event. It is a type of amnesia that leaves a lacuna (a gap) in the record of memory.
Characteristics
According to Steven Johnson, (the author of Mind Wide Open: Your Brain and the Neuroscience of Everyday Life):
"Scientists believe memories are captured and stored by two separate parts of the brain, the hippocampus, the normal seat of memory, and the amygdala, one of the brain's emotional centers. People who, due to hippocampus damage, are incapable of forming long-term memories can still form subconscious memories of traumatic events if their amygdala is intact. Someone suffering from the Memento condition would likely have a feeling of general unease encountering a person who had harmed them in the past, though they wouldn't be able to put their finger on why. As the plot of Eternal Sunshine correctly suggests, the brain is designed to preserve emotionally strong memories. Even amnesiacs, under the right circumstances, can remember their past feelings."
Furthermore, according to Alex Chadwick speaking on NPR:
"Some scientists now believe that memories effectively get rewritten every time they're activated. Studies on rats suggest that if you block a crucial chemical process during the execution of a learned behavior - pushing a lever to get food, for instance - the learned behavior disappears. The rat stops remembering. Theoretically, if you could block that chemical reaction in a human brain while triggering a specific memory, you could make a targeted erasure. Think of a dreadful fight with your girlfriend while blocking that chemical reaction, and zap! The memory's gone."[1]
Daniel Goleman, in his book Vital Lies, Simple Truths, defines a lacuna as :
"... lacuna, from the Latin for gap or hole, to refer to the sort of mental apparatus that diversionary schemas represent. A lacuna is, then, the attentional mechanism that creates a defensive gap in awareness. Lacunas, in short, create blind spots"[2]
Popular culture
This type of amnesia is used as a plot element in the 2004 movie Eternal Sunshine of the Spotless Mind, in which a company (appropriately named Lacuna) offers the service of having a specific person erased from someone's memories by removing all memories of them.
Similarly, in the manga Fruits Basket, the character Hatori Sohma has the ability to erase a persons memories. This ability is used by the head of the family, Akito, who instructed Hatori to use it when people outside the family discovered their secret. He also had to use the ability to make his fiancee, Kana, forget about him because he'd caused her too much pain.
In the popular 1988 manga Ranma ½, a titular "Chinese Amazon Woman", Shampoo, has the ability to manipulate someone's memories, as she did to main character Akane. She removed any memories Akane had of Ranma, and as a result, Ranma had to find a way to restore Akane's memories.
In the 1977 movie Heroes the protagonist Jack Dunne (Henry Winkler) learns a horrible truth about a friend of his about which he had known, but has forgotten.
In the last episode of the fourth series of the 2005 revival of Doctor Who, the character Donna Noble experiences amnesia of this sort when her memories are altered to remove any trace of the Doctor, aliens, or any sort of unearthly strangeness to prevent her mind from burning itself up.
In the Korean drama Boys Over Flowers, the male protagonist, Gu Jun Pyo, forgets the female protagonist, Geum Jan Di, after being hit by a car.
This type of amnesia is seen in the Star Wars expanded universe novel I, Jedi, in which the lead character and narrator Corran Horn forgets everything about his wife Mirax Terrik, following her mysterious disappearance.
In the Star Trek Original Series episode "And the Children Shall Lead" (1968), a group of children appear unaffected by the mass suicide of their parents. Dr McCoy makes a diagnosis of lacunar amnesia.