“We need to remember not just what happened, but when,” said Liang-Tien (Frank) Hsieh, a graduate student at the University of California, Davis, Center for Neuroscience and first author on the study,
For the study, Hsieh and Charan Ranganath, Ph.D., a professor in the Department of Psychology and the Center for Neuroscience, looked for hippocampus activity linked to particular memories.
First, they showed volunteers a series of pictures of animals and objects. Then they scanned the volunteers’ brains as they showed them the same series again, with questions such as, “is this alive?” or “does this generate heat?”
The questions prompted the volunteers to search their memories for information. When the images were shown in the same sequence as before, the volunteers could anticipate the next image, making for a faster response, the researchers report.
From scans of the hippocampus as the volunteers were answering questions, Hsieh and Ranganath could identify patterns of activity specific to each image. But when they showed the volunteers the same images in a different sequence, they got different patterns of activity.
In other words, the coding of the memory in the hippocampus was dependent on its context, not just on content, according to the researchers.
“It turns out that when you take the image out of sequence, the pattern disappears,” Ranganath said. “For the hippocampus, context is critical, not content, and it’s fairly unique in how it pulls things together.”
Other parts of the brain store memories of objects that are independent of their context, Ranganath noted.
“For patients with memory problems this is a big deal,” Ranganath said. “It’s not just something that’s useful in understanding healthy memory, but allows us to understand and intervene in memory problems.”
The study is published in the journal Neuron.
Source: University of California, Davis