Neurobiologists have figured out how to make mice forget traumatic experiences:
For more than two decades, researchers have been studying the chemical–a protein called alpha-CaM kinase II–for its role in learning and memory consolidation.
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He and his collaborators first put the mice in a chamber where the animals heard a tone, then followed up the tone with a mild shock. The resulting associations: the chamber is a very bad place, and the tone foretells miserable things.
Then, a month later–enough time to ensure that the mice’s long-term memory had been consolidated–the researchers placed the animals in a totally different chamber, overexpressed the protein, and played the tone. The mice showed no fear of the shock-associated sound. But these same mice, when placed in the original shock chamber, showed a classic fear response. Tsien had, in effect, erased one part of the memory (the one associated with the tone recall) while leaving the other intact.
Pretty cool. I assume controls were done with mice without the protein and that the tone elicited a similar fear response (although why didn’t Technology Review mention that?).
Why does the protein make the mice forget about the tone and not the place? Would they forget about the tone if they had played it while they were shocking them instead of just before?
October 22nd, 2008 - 7:12 pm
I like that you used a quote from Men in Black (men).
October 23rd, 2008 - 12:18 am
Although they probably should have mentioned it, it’s unnecessary to have that control group because it’s assumed that mice will exhibit the conditioned response (fear) at the first reintroduction of the conditioned stimulus (tone). Their control group is pretty much the millions of rats used in labs in the past century.
I think it’s interesting that there’s no mention of second-order conditioning here. Animals in general are good at associating a physiological stimulus with the most appropriate stimulus around. In this case, the tone is more likely the cause of the shock than is the general location, because of temporal proximity to the shock, i.e., the chamber did not immediately precede a shock, it was just there while the shock happened. But it’s not just time that matters; if you feed the mice poisoned sugar water and simultaneously play a tone, their response will be conditioned to the water flavor, not the tone. Because a food is more likely to cause the sickness, it’s treated as the first-order stimulus. So it’s odd that there’s no description of this mysterious chamber — usually a nondescript location is hard to condition to something like a shock.
Lastly, if they played the tone while shocking the mice, they probably wouldn’t even fucking hear it.
October 23rd, 2008 - 1:23 am
Yeah, I was just wondering if the protein blocked the memory of the tone but not the location for some weird reason like, it works on the auditory part of the brain or some shit. Or maybe it had something to do with the timing of a discrete event (the tone) as opposed to a constant environment (the chamber).
It makes sense that the mice would associate the shock with the most “appropriate” stimulus. And yet they were still freaked out by the chamber. Is that because the chamber was just appropriate enough to elicit a response, but not appropriate enough to be blocked by the protein? I guess that’s what you mean by a second-order stimulus.
So what if you shock the mice in the chamber with no tone, overexpress the protein, and then put them back in the chamber? Does the protein block the memory because without the tone, the chamber is the “most appropriate” (first-order) stimulus?