In a second set of oddball experiments, the researchers sought to determine whether the SN/VTA encodes the magnitude of novelty. In those experiments, the researchers measured activation of the region by images of different levels of familiarity or novelty. In yet other studies, the researchers assessed whether the subjects' memory of familiar images was better when presented along with novel images or very familiar images.

The researchers found that the SN/VTA does, indeed, respond to novelty, and these response scales according to how novel the image was. They concluded that their data provide evidence for "a functional hippocampal-SN/VTA loop" that is driven by novelty rather than other forms of stimulus salience such as emotional content or the need to respond to an image. The researchers said their finding that the SN/VTA is more activated by greater novelty is compatible with models of brain function "that see novelty as a motivating bonus to explore an environment in the search for reward rather than being a reward itself."

Also, Bunzeck and Dzel found that novelty enhanced learning in the subjects. "Thus, the human SN/VTA can code absolute stimulus novelty and might contribute to enhanced learning in the context of novelty," they concluded.

Finally, they said their findings raise the possibility that selective brain injury to the hippocampus could eliminate the positive effects of novelty in such patients and constitute one source of reduction in recognition memory in the patients.

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Contact: Heidi Hardman
hhardman@cell.com
617-397-2879
Cell Press
2-Aug-2006