Friday, February 26, 2016

The Brain’s Hippocampus: On Time & Spatial Memory


Place & Time Cells: Memory is located in various places of the brain, including the temporal lobes, and the structures of the limbic system. But it is the hippocampus that plays the most prominent role in a particular type of memory called spatial memory, which is used, for example, to find one’s way around a city. The website, The Brain From Top to Bottom writes:“Unlike our memory of facts and events, however, our spatial memory appears to be confined to the hippocampus. And more specifically to the right hippocampus. This structure seems to be able to create a mental map of space, thanks to certain cells called place cells.” The hippocampus might also be responsible for mapping time in what are referred to as time cells.
Image Credit & Source: McGill University

An article, by Emily Singer, in Quanta Magazine says that the area of the brain responsible for spatial mapping and memory is also responsible for time mapping and memory. Such is the conclusion of neuroscientists at Boston University in a research study led by Howard Eichenbaum. In “New Clues to How the Brain Maps Time” (January 26, 2016), Singer writes:
Over the last few years, a handful of researchers have compiled growing evidence that the same cells that monitor an individual’s location in space also mark the passage of time. This suggests that two brain regions — the hippocampus and the entorhinal cortex, both famous for their role in memory and navigation — can also act as a sort of timer.
In research published in November, Howard Eichenbaum, a neuroscientist at Boston University, and collaborators showed that cells in rats that form the brain’s internal GPS system, known as grid cells, are more malleable than had been anticipated. Typically these cells act like a dead-reckoning system, with certain neurons firing when an animal is in a specific place. (The researchers who discovered this shared the Nobel Prize in 2014.) Eichenbaum found that when an animal is kept in place — such as when it runs on a treadmill — the cells keep track of both distance and time. The work suggests that the brain’s sense of space and time are intertwined.
The findings help to broaden our understanding of how the brain’s memory and navigation systems work. Perhaps both grid cells and other GPS-like cells aren’t tuned only to space but are capable of encoding any relevant property: time, smell or even taste. “It probably points to a broad thing the hippocampus does,” said Loren Frank, a neuroscientist at the University of California, San Francisco, who studies memory and the hippocampus. “It figures out the relevant axis for encoding experiences and then uses the cells to map those experiences.”
It could well be that the hippocampus and the entorhinal cortex, which help an individual’s spatial orientation— might also be the centre of temporal management. The hippocampus, in particular, might play a very broad role in both spatial and temporal recognition and in how we account for and remember events—a result of both place cells and time cells firing hippocampal neurons. Although the idea might not sound revealing or surprisingly new, the article points out that time and space are connected, not only in our experiences (and long-term memories), but also in how different regions of the brain function.

One of the benefits of such research is that it might lead to ways to reverse the damage of memory loss and function in such degenerative diseases as dementia and Alzheimer’s. The entorhinal cortex, for example, is the first area of the brain to be affected by Alzheimer's disease.

For more, go to [Quanta]

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