To explore this mystery more deeply, the Salk scientists compared the functioning of the mouse dentate gyrus and another region of the hippocampus, known as CA1, using laboratory techniques for tracking the activity of neurons at multiple time points.
First, the researchers took mice from their original chamber and placed them in a novel chamber to learn about a new environment (episode 1). Meanwhile, they recorded which hippocampal neurons were active as the animals responded to their new surroundings. Subsequently, the mice were either returned to that same novel chamber to measure memory recall or to a slightly modified chamber to measure discrimination (episode 2). The active neurons in episode 2 were also labeled in order to determine if the neurons activated in episode 1 were used in the same way for recall and for discrimination of small differences between environments.
When the researchers compared the neural activity during the two episodes, they found that the dentate gyrus and CA1 sub-regions functioned differently. In CA1, the same neurons that were active during the initial learning episode were also active when the mice retrieved the memories. In the dentate gyrus, however, distinct groups of cells were active during the learning episodes and retrieval. Also, exposing the mice to two subtly different environments activated two distinct groups of cells in the dentate gyrus.
"This finding supported the predictions of theoretical models that different groups of cells are activated during exposure to similar, but distinct, environments," says Wei Deng, a Salk postdoctoral research and first author on the paper. "This contrasts with the findings of previous laboratory studies, possibly because they looked at different sub-populations of
|Contact: Andy Hoang|