"When hippocampal cells undergo these striking changes in neuronal activity, its like watching a new memory being born," explained Suzuki, whose research was funded by the National Institute of Mental Health (NIMH) and the National Institute on Drug Abuse (NIDA). "The key to detecting 'changing cells' was to keep the task simple so that the monkeys could easily learn multiple new associations within a single recording session."
The researchers measured activity of individual neurons in the hippocampus as two monkeys formed new associative memories while playing a computer game. The monkey had to gaze at one of four identical targets superimposed on a complex visual scene to win a juice reward. For example, white dots appeared at four locations over a picture of a gorilla in a forest. The animals learned, through trial and error, which location was associated with the reward for each new scene. Eye-tracking technology detected if the animal was fixated on the correct dot and the reward was dispensed. Monkeys learned 2-4 new associations during each recording session. It took about a dozen trials to establish the memory for each scene.
Among 89 neurons that responded to the scenes, the researchers discovered a subset of 25 "changing cells" whose increase or decrease in activity paralleled learni
Contact: Jules Asher
NIH/National Institute of Mental Health