Lega and his team found the time cells by studying the brains of 27 people who were awaiting surgery for severe epilepsy. As part of their pre-surgical preparation, these patients had electrodes placed in the hippocampus and another area of the brain involved in navigation, memory and time perception. In the experiment, the patients studied sequences of 12 or 15 words that appeared on a laptop screen during a period of about 30 seconds. Then, after a break, they were asked to recall the words they had seen. Meanwhile, the researchers were measuring the activity of individual brain cells. And they found a small number that that would fire at specific times during each sequence of words.
“The time cells that we found, they are marking out discrete segments of time within this approximately 30-second window,” Lega says. These time stamps seemed to help people recall when they had seen each word, and in what order, he says. And the brain probably uses the same approach when we’re reliving an experience like falling off a bike. The results help explain why people who have damage to the hippocampus may experience odd memory problems, Buzsaki says.
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