Researchers have long known that the brain links kinds of new facts, related or not, when they are learned about the same time. For the first time, scientists have recorded routes in the brain of that kind of contextual memory, the frequent change of thoughts and emotions that surrounds every piece of newly learned information.
The recordings, taken from the brains of people awaiting surgery for epilepsy（癫痫）, suggest that new memories of even abstract facts are encoded（编码） in a brain-cell order that also contains information about what else was happening during and just before the memory was formed.
In the new study, doctors from the University of Pennsylvania and Vanderbilt University took recordings from a small piece of metal implanted in the brains of 69 people with severe epilepsy. The implants allow doctors to pinpoint the location of the flash floods of brain activity that cause epileptic happening. The patients performed a simple memory task. They watched a series of nouns appear on a computer screen, and after a brief disturbance recalled as many of the words as they could, in any order. Repeated trials, with different lists of words, showed a predictable effect: The participants tended to remember the words in groups, beginning with one and recalling those that were just before or after.
This pattern, which scientists call the contiguity effect, is similar to what often happens in the card game concentration, in which players try to identify pairs in a row of cards lying face-down. Pairs overturned close are often remembered together. The way the process works, the researchers say, is something like reconstructing a night's activities after a hangover: remembering a fact (a broken table) recalls a scene (dancing), which in turn brings to mind more facts, like the other people who were there.
Sure enough, the people in the study whose neural（神经） updating signals were strongest showed the most striking pattern of remembering words in groups. "When you activate one memory, you are reactivating a little bit of what was happening around the time the memory was formed, and this process is what gives you that feeling of time travel," said Dr Michael J. Kahana.
