Erasing memories via memory reconsolidation

Pythagorean

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A review of memory reconsolidation[1], the recent experiment in which memory traces were attenuated[2] and a caveat that recovery of the fear memory is typical in patients [3].


[1]
Abstract said:
Memory reconsolidation has been argued to be a distinct process that serves to maintain, strengthen or modify memories. Specifically, the retrieval of a previously consolidated memory has been hypothesized to induce an additional activity-dependent labile period during which the memory can be modified. Understanding the molecular mechanisms of reconsolidation could provide crucial insights into the dynamic aspects of normal mnemonic function and psychiatric disorders that are characterized by exceptionally strong and salient emotional memories.
http://www.nature.com/nrn/journal/v8/n4/abs/nrn2090.html




[2]
Abstract said:
Memories become labile when recalled. In humans and rodents alike, reactivated fear memories can be attenuated by disrupting reconsolidation with extinction training. Using functional brain imaging, we found that, after a conditioned fear memory was formed, reactivation and reconsolidation left a memory trace in the basolateral amygdala that predicted subsequent fear expression and was tightly coupled to activity in the fear circuit of the brain. In contrast, reactivation followed by disrupted reconsolidation suppressed fear, abolished the memory trace, and attenuated fear-circuit connectivity. Thus, as previously demonstrated in rodents, fear memory suppression resulting from behavioral disruption of reconsolidation is amygdala-dependent also in humans, which supports an evolutionarily conserved memory-update mechanism.
http://www.sciencemag.org/content/337/6101/1550.abstract



[3]
Exposure-based treatments for clinical anxiety generally are very effective, but relapse is not uncommon. Likewise, laboratory studies have shown that conditioned fears are easy to extinguish, but they recover easily. This analogy is striking, and numerous fear extinction studies have been published that highlight the processes responsible for the extinction and return of acquired fears. This review examines and integrates the most important results from animal and human work. Overall, the results suggest that fear extinction is relatively easy to “learn” but difficult to “remember.” It follows that treatments will benefit from an enhanced focus on the long-term retrieval of fear extinction. We review the available studies on the prevention of return of fear and the prospects of weakening fear memories forever. We show that the behavioral principles outlined in learning theory provide a continuous inspiration for preclinical (neurobiological) and clinical research on the extinction and return of fear.
http://www.annualreviews.org/doi/abs/10.1146/annurev-clinpsy-050212-185542
 

atyy

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Let's say I'm a Sumerian kid who's afraid of school because I was bad at spelling and the teacher caned me. Does the erasure erase only the fear, or also that the memory that the teacher caned me?
 

Pythagorean

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I doubt the explicit autobiographical memory is erased. Only the implicit memory is erased and it can apparently be reconstructed (probably through the autobiographical memory).
 

Ygggdrasil

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There was also a recent paper from the Tonegawa lab where they used optogenetic techniques to implant a "false memory" into rats:

Memories can be unreliable. We created a false memory in mice by optogenetically manipulating memory engram–bearing cells in the hippocampus. Dentate gyrus (DG) or CA1 neurons activated by exposure to a particular context were labeled with channelrhodopsin-2. These neurons were later optically reactivated during fear conditioning in a different context. The DG experimental group showed increased freezing in the original context, in which a foot shock was never delivered. The recall of this false memory was context-specific, activated similar downstream regions engaged during natural fear memory recall, and was also capable of driving an active fear response. Our data demonstrate that it is possible to generate an internally represented and behaviorally expressed fear memory via artificial means.
Ramirez et al. 2013 Creating a False Memory in the Hippocampus. Science: 341, 387. doi:10.1126/science.1239073
 

atyy

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I doubt the explicit autobiographical memory is erased. Only the implicit memory is erased and it can apparently be reconstructed (probably through the autobiographical memory).
You're thinking this because of the third reference in the OP in which the fear returns after it has been extinguished?
 

Pythagorean

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Yes. The review (the third reference) goes into both extinguishing and reconsolidation (and a mixture of the two). It indirectly references the second reference in the OP. They don't explicitly say that the implicit memory returns because of declarative memory, that's speculation on my part.

Interestingly, another reference in the review did actually find an affect on declarative memory:
http://www.sciencedirect.com/science/article/pii/S030105111200021X
 

Pythagorean

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There was also a recent paper from the Tonegawa lab where they used optogenetic techniques to implant a "false memory" into rats:

Ramirez et al. 2013 Creating a False Memory in the Hippocampus. Science: 341, 387. doi:10.1126/science.1239073
Here's the psychology equivalent from all the way back in '95:
http://www.grangebehaviouralsciences.com/uploads/1/0/1/9/10197659/loftusmem1.pdf

If I remember correctly, they basically ask people to recall a memory and ask them questions about it, but some of the questions are loaded (i.e. assume a false pretense). Later, when asked about it, ~30% of people believe the false pretense to be a true part of their memory.
 

atyy

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Yes. The review (the third reference) goes into both extinguishing and reconsolidation (and a mixture of the two). It indirectly references the second reference in the OP. They don't explicitly say that the implicit memory returns because of declarative memory, that's speculation on my part.

Interestingly, another reference in the review did actually find an affect on declarative memory:
http://www.sciencedirect.com/science/article/pii/S030105111200021X
By declarative memory are you referring to "At a cognitive level, propranolol directly impaired extinction learning." ? (Sorry, I should read this myself, but am too lazy, so I'll just ask you:)
 

Pythagorean

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yeah, declarative/explicit/consciously available memories like autobiographical/episodic as opposed to implicit/unconscious memories like procedural.
 

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