The fallacy of memory
How your brain can remember things that never happened
JoAnn Taylor remembers the texture of the pillow and the weight of it in her hands as she pressed it down on a 65 year-old widow’s face, snuffing out her life. She confessed to the murder in 1989, recounting the incident in great detail. After serving close to two decades in prison, she was acquitted in 2009 when DNA testing showed beyond the shadow of a doubt that she wasn’t even present at the crime scene. Why then did she have such vivid memories of committing the crime?
The arrest and exoneration of Taylor and her co-defendants is one of the most sensational cases in recent US history. But its not the only one. Hundreds of men and women have confessed to crimes they did not commit and were later pardoned based on DNA evidence.
Human memory, it turns out, is like putty. It can be shaped and altered with coercion and repetition. If I told you enough times that you had a lemon tree in the backyard of your childhood home and inserted enough details from your past to make it seem real, you may eventually start to picture the non-existent lemon tree in your mind. Depending on how coercive I am and how open you are to suggestion, you may even smell its citrus scent. Psychologists have shown that with suggestive memory-retrieval techniques and repetitive interviews, 70% of an experiment’s participants volunteered rich accounts of a crime they hadn’t committed. So what goes on in the brain when it churns out false memories?
The neurobiology of false memories
Most of us can remember the time of day, where we were, what we were doing, and how we felt when we first heard about the collapse of the World Trade Center on September 11, 2001. This ability to remember our surroundings and our emotional response to a particular event is called contextual memory. The physical and chemical representation of such a memory in the brain is called an engram.
Scientists were able to identify memory engrams by developing genetically modified mice whose neurons lit up when activated during memory formation. To identify the cellular mechanisms involved in the formation of false memories, these genetically modified mice were first placed in a box of specific dimensions, color, and smell. Let’s call this box the Beach. The neurons responsible for forming a memory of the Beach were identified. Next, these mice were placed in another box with different dimensions, color, and smell. Let’s call this box the Prison.
While in the Prison box, they were given a mild foot shock while simultaneously activating memories of the Beach box. This was done by shining light of a specific wavelength on those neurons that encoded the Beach memory, a technique called optogenetics. When the mice were subsequently placed back in the Beach box they froze, their posture tense and rigid instead of relaxed — a textbook fear response in mice. A false fear memory was thus created in the mice where they mistakenly associated the Beach with a foot shock, even though they had never experienced pain in the Beach box before.
False memories: Bane or boon?
Humans are highly imaginative beings. False memories are perhaps the Achilles heel of human imagination, blurring the lines between fact and fiction. It is a scary world indeed if we cannot trust the one thing that makes us who we are — our memories. The fallibility of human memory has been demonstrated time and again during eyewitness accounts of criminal proceedings when details about a suspect’s hair color, height, clothes, etc. are often misremembered.
In JoAnn Taylor’s case, the fallability of her memory led to 20 years of incarceration. It turns out that as a child JoAnn was repeatedly sexually abused by her stepfather. And every time he held a pillow over her face to muffle her screams. The memory of that pillow evoked false memories in her mind of a murder she did not commit. Much like the mice that displayed fearful behavior in the safe environment of the Beach box.
But what if the amorphous nature of memory was used to alleviate human suffering? A proof-of-concept study in genetically engineered mice showed that replacing sad memories with happy ones could combat depression. Depression was induced in laboratory mice by preventing them from moving about for a couple of hours each day. Loss of interest in pursuing their naturally escapist behaviors or in seeking sugar water for pleasure was classified as depressive behavior in these mice. However, when neurons encoding a previous positive memory (such as play time with a female mouse) were light-activated, these depressive behaviors were substantially reduced. And the longer these happy memories were activated for, the less depressed the mice got.
Although these experiments conjure up notions akin to the movie Eternal Sunshine of a Spotless Mind where unhappy memories can be erased with a simple procedure, they are far from being a reality. The technology to alter human memory in a safe, effective, and ethical manner is currently lacking. Perhaps we should already be having an active conversation about the ethics of altering memories. Because if history is any indication, bad things happen when morals play catch-up with technology.
Twitter: @NeuroRaeesa
