Scientists are now able to wipe a single, specific memory from the brains of rats, leaving other memories intact.
... they trained rats to fear two different musical tones, by playing them at the same time as giving the rats an electric shock. Then, they gave half the rats a drug known to cause limited amnesia (U0126, which is not approved for use in people), and reminded all the animals, half of which were still under the influence of the drug, of one of their fearful memories by replaying just one of the tones.
When they tested the rats with both tones a day later, untreated animals were still fearful of both sounds, as if they expected a shock. But those treated with the drug were no longer afraid of the tone they had been reminded of under treatment. The process of re-arousing the rats' memory of being shocked with the one tone while they were drugged had wiped out that memory completely, while leaving their memory of the second tone intact.
http://www.nature.com/news/2007/070305/full/070305-17.html - via A Welsh View