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What happened when? How the brain stores memories by time

Date:
March 13, 2014
Source:
University of California - Davis
Summary:
New research shows that a part of the brain called the hippocampus stores memories by their "temporal context" -- what happened before, and what came after -- and not by content. From brain scans of the hippocampus as the volunteers were answering questions in this study, researchers 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.

Looking at photos (stock photo). Very often, our memories must distinguish not just what happened and where, but when an event occurred -- and what came before and after. New research from the University of California, Davis, Center for Neuroscience shows that a part of the brain called the hippocampus stores memories by their "temporal context" -- what happened before, and what came after.
Credit: © mariiya / Fotolia

Before I left the house this morning, I let the cat out and started the dishwasher. Or was that yesterday? Very often, our memories must distinguish not just what happened and where, but when an event occurred -- and what came before and after. New research from the University of California, Davis, Center for Neuroscience shows that a part of the brain called the hippocampus stores memories by their "temporal context" -- what happened before, and what came after.

"We need to remember not just what happened, but when," said graduate student Liang-Tien (Frank) Hsieh, first author on the paper published March 5 in the journal Neuron.

The hippocampus is thought to be involved in forming memories. But it's not clear whether the hippocampus stores representations of specific objects, or if it represents them in context.

Hsieh and Charan Ranganath, 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.

From brain 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.

"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."


Story Source:

The above story is based on materials provided by University of California - Davis. Note: Materials may be edited for content and length.


Journal Reference:

  1. Liang-Tien Hsieh, Matthias J. Gruber, Lucas J. Jenkins, Charan Ranganath. Hippocampal Activity Patterns Carry Information about Objects in Temporal Context. Neuron, 2014; 81 (5): 1165 DOI: 10.1016/j.neuron.2014.01.015

Cite This Page:

University of California - Davis. "What happened when? How the brain stores memories by time." ScienceDaily. ScienceDaily, 13 March 2014. <www.sciencedaily.com/releases/2014/03/140313092723.htm>.
University of California - Davis. (2014, March 13). What happened when? How the brain stores memories by time. ScienceDaily. Retrieved July 31, 2014 from www.sciencedaily.com/releases/2014/03/140313092723.htm
University of California - Davis. "What happened when? How the brain stores memories by time." ScienceDaily. www.sciencedaily.com/releases/2014/03/140313092723.htm (accessed July 31, 2014).

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