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 in the cortex region of the brain. The cause of this type of amnesia is the result of brain damage to the limbic system which control our memories and emotions.
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.
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
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 removal of all memories of a specific person from someone’s memory.