Why we tend to forget 'where we parked our cars '

In a new study, scientists have explained why we are not able to remember and locate where exactly had we parked our car in a parking lot.

Researchers at University of California, San Diego School of Medicine have induced this all-too-common human experience - or a close version of it - permanently in rats and from what is observed perhaps derive clues about why strokes and Alzheimer's disease can destroy a person's sense of direction.

Grid cells and other specialized nerve cells in the brain, known as "place cells," comprise the brain's inner GPS, the discovery of which earned British-American and Norwegian scientists this year's Nobel Prize for medicine.

In research that builds upon the Nobel Prize-winning science, UC San Diego scientists have developed a micro-surgical procedure that has made it possible to remove the area of the rat's brain that contains grid cells and show what happens to this hard-wired navigational system when these grid cells are wiped out.

One effect, not surprisingly, was that the rats became very poor at tasks requiring internal map-making skills, such as remembering the location of a resting platform in a water maze test.

Senior co-author Robert Clark said that their loss of spatial memory formation was not a surprise, since it was what would be expected based on the physiological characteristics of that area of the brain, the entorhinal cortex, which is the first brain region to break down in Alzheimer's disease.

It was surprising that the type of memory formation was not disrupted by the removal of the grid cell area, Clark added.

The scientists were able to show that even without grid cells rats could still mark spatial changes in their environment. Electrical recordings of signals transmitted from the hippocampus suggested that the animals had developed place cells - cells that are believed to convey a sense of location - and that these cells were firing when an animal passed through a familiar place.

Clark said that their work showed a crisp division of labor within memory circuits of the brain. Removing the grid-cell network removed memory for places but left completely intact a whole host of other important memory abilities like recognition memory and memory of fearful events.

The findings are published online in Cell Reports.