Amnesia has provided many a plot twist for soap operas and movies, yet few of us ever encounter a real life example of this syndrome. That said, anyone who has undergone a medical procedure involving certain kinds of anesthesia has experienced a temporary, drug-induced version of amnesia. We wake with no memory of the surgical team’s conversation or the tunes they played while removing our tonsils. Given the fact that nearly 250 million patients “go under” during one or another medical procedure each year, controlled amnesia is a relatively common experience.

However, we are only interested in the uncontrolled variety of memory gaps: what can science tell us about that?

Let’s begin with the ordinary. The most familiar version of an amnesic gap is one you probably don’t even think of as such. With rare exception, most of us experience infantile amnesia, or the inability to recall memories from early childhood. In fact, most of our first four years are a complete blank despite the fact that we retain language and habits acquired in those years. What causes this? While psychologists point to repression and linguists focus on the lack of language, neuroscientists at the University of Toronto theorize the rapid rate at which new cells form in our earliest years pushes out established memory circuits. And so we forget.

infantile amnesia
Infantile amnesia is the inability to recall memories from early childhood. Photo courtesy of Shutterstock.

Outside of infantile amnesia, the experience of this syndrome is far from a one-size fits all experience. For instance, retrograde amnesia occurs when any memories you created prior to some causal event (say, a brain injury) are forgotten yet, going forward, you are able to create new memories. By comparison, anterograde amnesia occurs when you lose your ability to create new memories following some causal event, though memories from your long-ago past remain intact. Both types of amnesia can occur at the same time, but this is not common.

People who develop anterograde amnesia usually do so as a result of drugs or traumatic brain injury. Benzodiazepine drugs have amnesic effects, as do some sedatives (including the popular Ambien). When the hippocampus, the brain region for memory (and the part of our brain that goes in patients with Alzheimer’s), is harmed as a result of a traumatic brain injury, anterograde amnesia may be the result. Shock or encephalitis may also cause this form of amnesia, but they do so only rarely.

Both of these instances of mental disorder, though radically different, are considered forms of simple amnesia in that they involve an absolute loss of information from your memory. Just as water escapes a leaky bucket, the memories are quite simply gone, never to return.

Anterograde amnesia
Anterograde amnesia occurs when you lose your ability to create new memories while memories from your long-ago past remain intact. Photo courtesy of Shutterstock.

Dissociative amnesia, formerly called psychogenic amnesia, occurs when "the person has deficits in memory for personal life history/autobiographical memory that is not consistent with studies of autobiographical memory in non-clinical populations," Dr. Richard Loewenstein, M.D., the Medical Director of the Trauma Disorders Program at Sheppard Pratt Health System, told Medical Daily. "In general, these deficits are associated with traumatic/severely stressful life events." The extent of memory loss goes far beyond normal forgetfulness and lingers over long periods of time. However, this type of amnesia is not the same as simple forms of amnesia. With dissociative amnesia, the memories still exist even if they cannot be recalled and so there remains the hope that the memories might someday resurface.

Psychiatrists have identified two distinct types of dissociative amnesia. Global amnesia, also known as fugue state, refers to a sudden loss of identity lasting a few hours or days and often involves extended periods of wandering and confusion. Situation-specific amnesia occurs as a result of a severely stressful event and is a loss of memory surrounding only that event. In such cases, a person would only draw a blank when asked questions about being attacked by a stranger, say, or of escaping a fire. All other memories would remain intact.

"Dissociative amnesia and memory problems are part of the core symptoms of PTSD," Loewenstein told Medical Daily. "Often, people with PTSD will have flashbacks, but then have dissociative amnesia for the flashback, or will have dissociative amnesia for parts of the trauma that led to the PTSD." A diagnosis of dissociative amnesia would only given when the memory deficits go beyond the trauma and "involve more extensive aspects of the person’s memory for their life history," he explained.

Dissociative amnesia is more common in women than in men and scientists believe genes may be involved since certain people have a tendency to develop this condition. In fact, it runs in families. "Conservatively, five to six percent of the general population may have experienced the dissociative amnesia disorder during their lifetime," said Loewenstein, explaining how different studies may indicate different levels of frequency. That said, "dissociative fugue is rare," he said, occurring mostly in extreme circumstances such as soldiers during wartime or trafficked people, say.

While no laboratory tests exist to diagnose dissociative disorders, most doctors would want to rule out illness, injuries, or drugs as a cause so people with amnesia generally undergo various blood tests and examinations. Once referred to a psychiatrist or psychologist, you would be evaluated and treated, generally with psychotherapy or cognitive therapy.

"I have treated hundreds of patients with this disorder, both the generalized type and the type with autobiographical disturbances for life history," Loewenstein told Medical Daily. "They do well when provided appropriate treatment, although some remain impaired and highly symptomatic, as with any psychiatric patient group. In general, the amnesia is treated in the context of treating the person’s overall severe posttraumatic disorder." The goal of treatment would be the expression and processing of painful memories in order to help restore functioning. It also may involve treatment of many other symptoms and issues, "including depression, suicide attempts, self-destructive and/or other high-risk behaviors; substance abuse, eating disorders, and PTSD, among others," said Loewenstein.

For most dissociative amnesia patients, memory returns in time though in some cases, patients never retrieve their memories and in the case of one patient posting online, her amnesia recurs again and again. This anonymous patient notes that she endured four separate episodes lasting from four days to three years over a period of a decade.

“Stress brings on these times when I just go within my mind and close the doors, at least that’s what it feels like to me,” she writes.

The YouTube video below, courtesy of Firecracker films, offers you a perspective of a patient suffering from dissociative amnesia.