May 2, 2020 10:48 PM
https://www.the-scientist.com/features/h...ries-67443
INTRO: No matter how he looked at the data, Albert Tsao couldn’t see a pattern. Over several weeks in 2007 and again in 2008, the 19-year-old undergrad trained rats to explore a small trial arena, chucking them pieces of tasty chocolate cereal by way of encouragement. He then recorded the activity of individual neurons in the animals’ brains as they scampered, one at a time, about that same arena. He hoped that the experiment would offer clues as to how the rats’ brains were forming memories, but “the data that it gave us was confusing,” he says. There wasn’t any obvious pattern to the animals’ neural output at all.
Then enrolled at Harvey Mudd College in California, Tsao was doing the project as part of a summer internship at the Kavli Institute for Systems Neuroscience in Norway, in a lab that focused on episodic memory—the type of long-term memory that allows humans and other mammals to recall personal experiences (or episodes), such as going on a first date or spending several minutes searching for chocolate. Neuroscientists suspected that the brain organizes these millions of episodes partly according to where they took place. The Kavli Institute’s Edvard Moser and May-Britt Moser had recently made a breakthrough with the discovery of “grid cells,” neurons that generate a virtual spatial map of an area, firing whenever the animal crosses the part of the map that that cell represents. These cells, the Mosers reported, were situated in a region of rats’ brains called the medial entorhinal cortex (MEC) that projects many of its neurons into the hippocampus, the center of episodic memory formation.
Inspired by the findings, Tsao had opted to study a region right next to the MEC called the lateral entorhinal cortex (LEC), which also feeds into the hippocampus. If the MEC provided spatial information during memory formation, he and others had reasoned, maybe the LEC provided something else, such as information about the content of the experience itself. Tsao had been alternating the color of the arena’s walls between trials, from black to white and back again, to see if LEC neurons showed consistently different firing patterns in each case. But he was coming up empty-handed.
While Tsao struggled to make sense of his data, a researcher on the other side of the Atlantic Ocean was tackling a seemingly un-related problem. Marc Howard, a theoretical and computational neuroscientist then at Syracuse University, had filled a chalkboard with equations describing how the brain might achieve the complex task of organizing memories, according not to where they were formed, but to when. His mathematical model showed that if the passing of time was represented in a certain way in neural circuits, then that time signal could be converted into a series of mental “time stamps” during memory formation to help the brain organize past experiences in chronological order. Without data to confirm his model, however, the idea remained just that: an idea.
It would be several years before the two researchers became aware of each other’s work. By the time they did, neuroscientists had started thinking in new ways about how the brain keeps track of when experiences occurred. Today, the theoretical and experimental advances made by Howard, Tsao, and others in this field are helping to reshape researchers’ understanding of how episodic memories are formed, and how they might influence our perception of the past and future... (MORE)
INTRO: No matter how he looked at the data, Albert Tsao couldn’t see a pattern. Over several weeks in 2007 and again in 2008, the 19-year-old undergrad trained rats to explore a small trial arena, chucking them pieces of tasty chocolate cereal by way of encouragement. He then recorded the activity of individual neurons in the animals’ brains as they scampered, one at a time, about that same arena. He hoped that the experiment would offer clues as to how the rats’ brains were forming memories, but “the data that it gave us was confusing,” he says. There wasn’t any obvious pattern to the animals’ neural output at all.
Then enrolled at Harvey Mudd College in California, Tsao was doing the project as part of a summer internship at the Kavli Institute for Systems Neuroscience in Norway, in a lab that focused on episodic memory—the type of long-term memory that allows humans and other mammals to recall personal experiences (or episodes), such as going on a first date or spending several minutes searching for chocolate. Neuroscientists suspected that the brain organizes these millions of episodes partly according to where they took place. The Kavli Institute’s Edvard Moser and May-Britt Moser had recently made a breakthrough with the discovery of “grid cells,” neurons that generate a virtual spatial map of an area, firing whenever the animal crosses the part of the map that that cell represents. These cells, the Mosers reported, were situated in a region of rats’ brains called the medial entorhinal cortex (MEC) that projects many of its neurons into the hippocampus, the center of episodic memory formation.
Inspired by the findings, Tsao had opted to study a region right next to the MEC called the lateral entorhinal cortex (LEC), which also feeds into the hippocampus. If the MEC provided spatial information during memory formation, he and others had reasoned, maybe the LEC provided something else, such as information about the content of the experience itself. Tsao had been alternating the color of the arena’s walls between trials, from black to white and back again, to see if LEC neurons showed consistently different firing patterns in each case. But he was coming up empty-handed.
While Tsao struggled to make sense of his data, a researcher on the other side of the Atlantic Ocean was tackling a seemingly un-related problem. Marc Howard, a theoretical and computational neuroscientist then at Syracuse University, had filled a chalkboard with equations describing how the brain might achieve the complex task of organizing memories, according not to where they were formed, but to when. His mathematical model showed that if the passing of time was represented in a certain way in neural circuits, then that time signal could be converted into a series of mental “time stamps” during memory formation to help the brain organize past experiences in chronological order. Without data to confirm his model, however, the idea remained just that: an idea.
It would be several years before the two researchers became aware of each other’s work. By the time they did, neuroscientists had started thinking in new ways about how the brain keeps track of when experiences occurred. Today, the theoretical and experimental advances made by Howard, Tsao, and others in this field are helping to reshape researchers’ understanding of how episodic memories are formed, and how they might influence our perception of the past and future... (MORE)