Summary: New evidence suggests the brain can update poorly formed memories with incorrect information, leading to the creation of false memories.
Source: University of Technology Sydney
Senior author Professor Bryce Vissel, from the UTS Centre for Neuroscience & Regenerative Medicine, said his team used novel behavioural, molecular and computational techniques to investigate memories that have not been well-formed, and how the brain deals with them.
He explained, “For memories to be useful, they have to have been well-formed during an event – that is, they have to accurately reflect what actually happened.
“However, in the real world many memories are likely to be inaccurate – especially in situations where the experience was brief, sudden or highly emotional, as can often occur during trauma. Inaccurate memories can also occur when the memory is poorly encoded, potentially as a result of subtle differences in how each person processes memory or because of disease like Alzheimer’s or dementia.”
Lead author Dr Raphael Zinn said, “Our findings are exciting because they show that memory updating mechanisms that become activated after recall can refine and improve memories.
“Surprisingly, we found that the same process can, in some circumstances, lead to incorrect updating of the memory. We also identify one molecular mechanism, called reconsolidation, which could be mediating this process.”
“This suggests we might be able to target such updating mechanisms therapeutically to treat memory and anxiety disorders where memory formation is poor.”
The 6-year study shows that the same mechanism that updates poor memories can also severely distort them if it occurs in the wrong situation.
Professor Vissel said these findings could be useful for understanding memory fallibility in everyday life; fear and memory disorders, post-traumatic stress disorder (PTSD); and situations where accurate recall is critical, like witness testimony in courtrooms.
“While these findings come from studies in mice, this research is likely to apply across many animals with developed brains, including other mammals and humans. They might also tie in with dementias, where the main memory-related problem is an apparent inability to form accurate new memories.
“Why is memory fallible? Our study suggests that when an individual forms a poor memory, the brain reactivates the memory in a similar situation and then updates it. Sometimes a poorly formed memory can be wrongly reactivated in a similar, but irrelevant, situation. The brain may then update the memory from that irrelevant situation, causing the memory to become incorrect – rather than creating a new and entirely different memory of the new situation.”
This study was led by the UTS Centre for Neuroscience & Regenerative Medicine, in close collaboration with leading UCLA scientists Frank Krasne and Michael Fanselow.
Maladaptive Properties of Context-Impoverished Memories
The context in which sudden fearful events occur can be poorly encoded into memory. Yet, the consequences of the resulting context-impoverished memories remain unknown. We demonstrate that restricting the time available for context encoding during contextual fear conditioning causes maladaptively overgeneralized and inextinguishable fear. However, post-conditioning context exposure enables further context encoding through hippocampal reconsolidation-dependent memory updating. Updating in the conditioning context alleviates overgeneralization and restores capacity for extinction. However, updating in a similar safe context erroneously shifts fear from the dangerous to the safe context. We argue that these phenomena can be explained by uncertainty about where events occurred. Moreover, we show that a hippocampalneocortical neurocomputational model based on this assumption successfully simulates and explains our observations. These findings reveal that context-impoverished memories are maladaptive and can be improved or distorted after recall, with implications for basic memory theory, memory distortion, and treatment of disorders like post-traumatic stress disorder.