Remember this: Israeli researchers reveal inner workings of human memory

Israeli researchers reveal inner workings of human memory.

By JUDY SIEGEL-ITZKOVICH
neuron 88 (photo credit: )
neuron 88
(photo credit: )
Israeli scientists working in California have, for the first time, recorded individual brain cells in the act of calling up a memory; targeting where in the brain a specific memory is stored and how to recreate it. Prof. Itzhak Fried, head of the functional neurosurgery unit at Tel Aviv Sourasky Medical Center, a neurosurgery expert at Tel Aviv University and a neurosurgeon at the University of California at Los Angeles (UCLA), led the experiment, which was conducted with 13 epilepsy patients about to be operated on at UCLA Medical Center. Electrodes usually introduced into their brains to locate the origin of their seizures before surgery were used to record the firing of neurons. Fried's team at UCLA included Israelis Hagar Gelbard-Sagiv, Michal Harel and Rafael Malach of the Weizmann Institute of Science in Rehovot, and Roy Mukamel of UCLA. Their work, described by experts as "foundational" in explaining how recent memory works, was recently published in the journal Science. The recordings showed that recent memories "live" in some of the same neurons that fired most actively when the recalled event had been experienced, thus providing strong evidence, for the first time, in favor of a long-existing theory of neuroscientists. The finding is expected to lead to new directions in the study of dementias like Alzheimer's disease and help explain how some memories seem to come out of nowhere. "If we understand memory better," Fried told The Jerusalem Post before rushing off to surgery, "we are in better condition to help dementia patients. "The hippocampus region of the brain that we studied is the first to be affected by dementia. The ability to lay down new memories and retrieve them consciously depends on the hippocampus and the gateway to it, which is called the entorhinal cortex." The patients watched short video clips showing comic character Homer Simpson and some famous actors and comedians, along with landmarks like the Eiffel Tower. As they watched, researchers recorded the activity of many neurons in the hippocampus and the "gateway," which responded strongly to individual clips. A few minutes later, after performing an intervening task, the patients were asked to recall whatever clips came to mind. "They were not prompted to recall any specific clips," said Fried, "but to use free recall - that is, whatever popped into their heads." The researchers found that the same neurons that had responded earlier to a specific clip fired strongly a second or two before the subject reported what he had recalled (but did not fire when other clips were recalled). Ultimately, it was possible for the researchers to know which clips the patients were recalling without having to be told. The single neurons that were recorded as they fired, Fried said, were not acting alone, but were part of a much larger "memory circuit" of hundreds of thousands of cells caught in the act of responding to the clips. "In a way, then," said Fried, "reliving past experience in our memory is the resurrection of neuronal activity from the past."