Introducing the brain: the GPS system (Introduction)

by David Turell , Tuesday, May 29, 2018, 18:24 (2368 days ago) @ David Turell

Specialized neurons are identified:

https://www.quantamagazine.org/brains-positioning-system-linked-to-memory-20141007/

"In 1971, O’Keefe discovered special neurons called place cells, which fire whenever an animal is in a certain location. More recently, the Mosers identified grid cells, which are thought to act like a dead-reckoning system, telling the animal its location independent of external cues. Though first discovered in rats, both kinds of cells are widespread in mammalian brains, including those of humans.

"One striking feature of this system of grid and place cells is that it seems to encode abstract properties. “The big breakthrough is that these cells are not just responding to sensory cues, like an odor on the ground,” said David Redish, a neuroscientist at the University of Minnesota in Minneapolis. Instead, grid cells form an internal positioning system, and place cells use that information along with other cues to create a sense of place. Together, they create a rich map.

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"Rather than simply forming our inner GPS, place cells and grid cells may provide a system for anchoring our memories.

"Place cells are found in the hippocampus, which has long been considered the brain’s memory hub. Removing it, as happened with the famous patient H.M., wipes out the brain’s ability to form new memories. But O’Keefe’s discovery showed that the hippocampus is also essential for navigation.

"David Bishop, UCL O’Keefe recorded the impulses from neurons in a specific part of the hippocampus in rats as they explored an open space. He discovered that individual neurons would fire only when the rat was in a certain spot. By altering the surrounding environment, he showed that the animal wasn’t simply responding to sensory cues. Rather, the neurons were responding to a more sophisticated sense of location.

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"..the Mosers discovered a system of cells that are believed to provide spatial information to place cells. They probed individual neurons inside rats’ entorhinal cortex, an area of the brain that connects to the hippocampus. They then let the animals run around an empty space. Occasionally, the target neuron would fire. By mapping the points on the floor where this happened, the researchers discovered that the points where the neurons fired mapped out a grid of equilateral triangles. The arrangement was so well-defined that the researchers initially suspected an equipment malfunction.

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“'Once the Mosers discovered grid cells” — the neurons that fired in the grid pattern — “we had a new handle on the GPS part of the [memory] system.” (While GPS is a convenient metaphor, scientists believe that grid cells actually use a dead-reckoning system to calculate location.)

"One intriguing discovery is that grid cells can function in complete darkness, absent any visual cues. “This must reflect some internal brain dynamics that are in some sense independent of external sensory input,” Knierim said. “That’s one reason it’s so phenomenal — it gives us a window on understanding internal processing.”

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"Scientists have also used place cells to learn more about memory. As a rat runs through a maze, a particular sequence of place cells fire. The sequence replays after the rat goes to sleep; researchers think that this replay helps to transfer the rat’s memory of the maze from the hippocampus into long-term storage.

"More recent sleep studies suggest that the rat will replay the same pattern when it is in the maze again and needs to make a decision about where to go next. This may indicate that the rat is accessing memories of the maze as it mulls over the best path. “We know rats can do mental time travel,” Redish said, as they relive past events. “We are only able to know that because of place cells.”

"Many researchers believe that memory and space are even more intricately linked. In a popular trick for remembering speeches, dating back to ancient Greece, the orator calls to mind a familiar path through a city and attaches a segment of the speech to each location along the path. This mnemonic may unwittingly exploit the fact that the hippocampus encodes both location information and autobiographical memories. “It just happens that space is a good way of organizing experiences,” Wilson said."

Comment: This is part of conscious automatic brain activity we and animals have. It informs consciousness of what is happening.