From Nature:
A single, specific memory has been wiped from the brains of rats, leaving other recollections intact. The brain secures memories by transferring them from short-term to long-term storage, through a process called reconsolidation. It has been shown before that this process can be interrupted with drugs. But Joseph LeDoux of the Center for Neural Science at New York University and his colleagues wanted to know how specific this interference was.
To find out, 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.
More here.