It is well established that some experiences, such as stress, can strongly disrupt memory formation and recall. In particular, glucocorticoids, a hormone released from the adrenal glands, have an inhibitory effect on memory recall [4].
In recent a study exploring human memory consolidation and recall in stressful conditions showed that high levels of the glucocorticoid cortisol were significantly correlated with poor performance on memory tasks [7].
Human subjects in a “stressed” experimental group were asked to participate in a mock job interview in front of an audience of evaluators. In the middle of the interview, they were suddenly asked to recall vocabulary from a word association activity they participated in five weeks beforehand. The control group was simply asked to recall their words with these stressors removed.
The stressed group, researchers found, had elevated levels of cortisol in their saliva, as well as increased heart rate and blood pressures compared to control. Further, these stressed subjects performed worse in recalling “negative” word association vocabulary. However, it should be noted that stressed subjects were equally able to recall “neutral” word associations as non-stressed control.
The "Misinformation" Effect
Memory errors can extend beyond simply forgetting words under stress. In a series of now classic experiments, researchers have demonstrated that lasting and sometimes dramatic memory errors can occur.
In one study participants watched a video in which a traffic accident takes place near a stop sign. They then received a written summary of the accident and asked to recall, from memory, details about the video. If the summary substituted the stop sign for a yield sign, participants believed they had viewed a yield sign in the video, somehow adopting this into memory, in place of the stop sign that was actually there [4].
In a similar study, test subjects watched a video of a man stealing a girl’s wallet, with the girl sustaining a neck injury as a result. After watching the video, subjects were given a summary of the events that had occurred on screen. However, subjects were told that the girl had hurt her arm instead of her neck. When asked to recall the sequence of events in the video at a later time, almost half (47%) of the test subjects not only recalled an arm injury taking place during the sequence of events – they claimed to possess a visual memory of this occurrence [2].
This susceptibility of memory to fabrication has been called the “misinformation effect” by researchers. The sudden belief that one has seen something different than what actually occurred, just because it was verbally stated, is striking to say the least.
Are False Memories Ever Distinguishable?
Given that most people rely on their memory as an accurate source of information, important questions have been raised in response to this research. Is it possible to distinguish between an event that actually occurred, and one that did not?
Functional magnetic resonance imaging (fMRI) studies of false memory show that the Para hippocampus and sensory cortex are more active during true memory recall (for example: object recognition) than false [5]. Despite these differences in neural activity, conscious awareness of such false memories is still beyond the individual. So, while a test subject might confidently “remember” seeing a specific object, reduced activity in the Para hippocampus or sensory cortex suggest that such recognition is false.
While perhaps this is surprising, researchers hypothesize that in instances of false object recognition, these “memory” pathways are not as actively stimulated as in the case of true object recognition. Thus, generating less activity in these brain regions. Hypothetically, this better match would produce greater Para hippocampal activity, and a more active signal in an fMRI scan [5].
Malleability of Memory/False Implantation
Some researchers, in further exploring the misinformation effect, are trying to understand whether memory distortion can extend to complete fabrication. Altering a pre-existing memory seems fundamentally different than creating one that never existed.
The possibility of implanted memories first generated public interest in the late 20th century, when the psychotherapeutic practice of unearthing repressed memories came into vogue. Prominent media outlets covered stories of citizens who had recently undergone therapy and were subjected to aggressive therapeutic techniques, even to the point of taking hallucinatory “truth serum”, and then subsequently claiming to have unearthed years of familial abuse. In one such case, covered extensively by Time Magazine, a young woman, after undergoing such therapy, sued her father for years of sexual abuse, and also claimed to witness a murder that he perpetrated [1].
If a person can mentally replace a stop sign with a yield sign, is it possible that she could remember witnessing a murder that never actually occurred?
A variety of experiments, all with the same basic methodology, have shown that complex memories can be implanted.
The families of research participants were asked to share the details of several meaningful events that occurred during the participant’s childhood. The researchers then met with participants and discussed their memories of each event including one that the researchers had made up and included in the list.
Although many subjects did not initially remember the false memory - being lost at a shopping mall and returned to their family by an elderly person - repeated questioning led to about 30% of subjects reporting partial or even complete memories of the ordeal [2].
Being lost in a shopping mall is not an entirely unusual experience. So, some skepticism of this finding is warranted. However, in several follow-up studies, researchers have shown implanted memories that are fanciful, or even ridiculous. Participants have been led to believe and subsequently “remember” that they spent the night at the hospital for low blood sugar as children [2], that they once attended a wedding and spilled punch on the parents of the bride, or that they fled a grocery store after the overhead sprinklers spontaneously activated [1].
Participants in one study could even be made to believe that they had proposed marriage to a Pepsi machine on a college campus. If subjects either imagined themselves preforming this bizarre task, or witnessed someone else doing so, they adopted the memory as their own within two weeks. Subjects rated their confidence in having proposed to an inanimate object very highly [6].
Conclusion
Research into memory has made it clear that our recollections are not always as dependable as we assume them to be. Not only do studies suggest the ability to alter memories, but to implant them altogether. Such findings challenge us to rethink our understandings of the past, keeping the distortion of memory in mind as we do so.
References
- Izquierdo, Ivan, and Jorge H. Medina. "Memory Formation: The Sequence of Biochemical Events in the Hippocampus and Its Connection to Activity in Other Brain Structures." Neurobiology of Learning and Memory 68.3 (1997): 285-316. Print.
- Loftus, Elizabeth F. “Memory Distortion and False Memory Creation.” Bulletin of the American Academy of Psychiatry and the Law 24 (1996): 281-295. Print.
- Loftus, Elizabeth F. "Planting Misinformation in the Human Mind: A 30-year Investigation of the Malleability of Memory." Learning & Memory 12.4 (2005): 361-66. Print.
- Loftus, Elizabeth F. "When A Lie Becomes Memory's Truth: Memory Distortion After Exposure to Misinformation." Current Directions in Psychological Science 1.4 (1992): 121-23. Print.
- Otis, James M., Michael K. Fitzgerald, and Devin Mueller. "Inhibition of Hippocampal β-Adrenergic Receptors Impairs Retrieval But Not Reconsolidation of Cocaine-Associated Memory and Prevents Subsequent Reinstatement." Neuropsychopharmacology 39.2 (2013): 303-10. Print.
- Payne, David G., Claude J. Elie, Jason M. Blackwell, and Jeffrey S. Neuschatz. "Memory Illusions: Recalling, Recognizing, and Recollecting Events That Never Occurred." Journal of Memory and Language 35.2 (1996): 261-85. Print.
- Rao, Vikram R., and Steven Finkbeiner. "NMDA and AMPA Receptors: Old Channels, New Tricks." Trends in Neurosciences 30.6 (2007): 284-91. Print.
- Roozendaal, Benno. "Stress and Memory: Opposing Effects of Glucocorticoids on Memory Consolidation and Memory Retrieval." Neurobiology of Learning and Memory 78.3 (2002): 578-95. Print.
- Schacter, Daniel L., and Scott D. Slotnick. "The Cognitive Neuroscience of Memory Distortion." Neuron 44.1 (2004): 149-60. Print.
- Seamon, John G., Morgan M. Philbin, and Liza G. Harrison. "Do You Remember Proposing Marriage to the Pepsi Machine? False Recollections from a Campus Walk." Psychonomic Bulletin & Review 13.5 (2006): 752-56. Print.
- Tollenaar, Marieke S., Bernet M. Elzinga, Philip Spinhoven, and Walter A.m. Everaerd. "The Effects of Cortisol Increase on Long-term Memory Retrieval during and after Acute Psychosocial Stress." Acta Psychologica 127.3 (2008): 542-52. Print.