Jun
9
In Science this week, MIT neuroscientist Susumu Tonegawa and colleagues describe their recent research illuminating the biological mechanisms behind the sensation of déjà vu. (The journal paper is locked up, but there’s a good Scientific American account of the research.) The authors conclude that a set of neurons located in the hippocampus — specifically in an area called the dentate gyrus — fire to create a blueprint of a particular location. When that neural circuit is triggered incorrectly, set off perhaps by similarity between elements of a new location and one we have been to, we experience the sensation of déjà vu. Tonegawa used a clever mouse model to provide evidence for the hypothesis (from the MIT description):
In experiments with mice genetically engineered to lack a certain gene in the dentate gyrus, Tonegawa and colleagues pinpointed the signaling pathway underlying the recall of specific places.
Different sets of mice were placed in two similar chambers, one of which gave them a mild foot shock. After three days, the mice began to freeze in fear in both chambers, even the one in which they had never been harmed.
Within two weeks, the normal mice learned to associate only one chamber with the foot shocks while recognizing the second as safe. The genetically engineered mice “had a significant but transient deficit in their ability to distinguish similar contexts,” McHugh said.
The theory fits well with the Chris Moulin’s research at the University of Leeds, which I wrote about in the New York Times Magazine last year. The neurons Tonegawa identified in the hippocampus mirror the “recollective experience circuit” that Moulin and his colleagues hypothesized as the source of déjà vécu, a condition of persistent déjà vu:
Their hypothesis rested on the understanding, established in the wake of Tulving’s research, that episodic memories consist of two aspects: the information content, or “memory trace,” and an accompanying experience of recollection. It’s that experience, a little bit of consciousness attached to a memory, that lets us know that we are calling up something from the past. If someone experienced that feeling constantly, without any memory trace attached, they would feel — as Conway describes it — as if they were “remembering the present.” In other words, déjà vécu. …
…Moulin and Conway concluded that their patients’ déjà vécu was similarly located in the temporal lobes, in a “recollective experience circuit” that regulates the process of remembering. If the circuit was “continuously active,” it would keep feeding the brain that feeling of recollection, without any real memory attached.
Could ordinary déjà vu be a minor version of the same thing, a brief misfire in a temporal-lobe circuit that sets off the feeling of remembering? “Somebody like A.K.P. shows that there is this sensation that is separate from memory,” Moulin told me. “If his can go chronically wrong, ours can go momentarily wrong.”
Although it’s likely an overstatement to say, as the MIT researchers do (in the Reuters account) that “one big question about the memory is now taken care of,” the work is undoubtedly a significant piece of the déjà vu puzzle.
This entry was posted on Saturday, June 9th, 2007
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Deja vu : Atavistic on
December 12th, 2007 11:17 am
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