In a new basic science discovery about the brain, 1998 NARSAD Distinguished Investigator Grantee Larry R. Squire, Ph.D., and colleagues at the University of California, San Diego (UCSD) found that even if the brain’s “GPS system” is removed, parts of spatial memory are still intact. This information has important implications because the areas of the brain the researchers studied are among the first to be affected by Alzheimer’s disease.

Their results were published November 6th in Cell Reports. In the article, Dr. Squire describes a fascinating series of experiments they performed on rodents. The experiments were based on a surgical procedure to remove a central processing area called the MEC (medial entorhinal cortex), which feeds data into the hippocampus from various parts of the cortex, and receives data flowing out of it for distribution across the cortex.

Rodents, like humans, have two hippocampi––small seahorse-shaped formations on either side of the brain. They are central in the formation and retention of memory, and also play a key role in providing us with an accurate spatial sense of the world around us.  

For Dr. Squire, 2012 recipient of the Foundation’s Goldman-Rakic Prize for Outstanding Achievement in Cognitive Neuroscience, and his colleagues, the chief question was simple: If the MEC “processor” is removed, will rodents lose their sense of spatial memory? The short answer is “no.” Although rats with missing MECs performed poorly in a water maze that tested spatial memory, “they were not impaired on other hippocampus-dependent tasks,” including those in which the animal needed to remember the location of an object or something contextual about it. In human terms that would translate to, “I remember what my car looks like, and I remember that I parked it across the street last night.”)

It is known that the MEC and a neighboring region called the LEC are the first brain areas savaged in Alzheimer’s disease. The work also sheds light on the “inner GPS system” that we and other mammals possess. This year’s Nobel Prize for Physiology or Medicine was awarded to three scientists who discovered a key part of the system–– specialized cells called grid cells. They are one of a class of brain cells called “place cells” that together make up our inner GPS.

The removed portion of the rat brain, the MEC, contains grid cells. But the hippocampus itself contains a variety of place cells, which continued to operate. “The surprise of our experiments is the discovery of the type of memory formation that was not disrupted by the removal of the grid cells area,” says Robert Clark, Ph.D., leader of the UCSD team. Even without the grid cells, the rats could mark spatial changes in their environment. For example, they noticed when an object in a familiar place was moved. They could also recognize objects and later remember that they had seen them.  

Read the abstract of this research paper.