Animal Study Shows Memories Of Familiar Environments Can Survive After Brain Damage That Results In Severe Amnesia

Toronto researchers have demonstrated in a brain injury study with rats that extensive experience in a spatial environment increases the likelihood that those spatial memories will be preserved after an injury to the hippocampus that results in severe amnesia.

The study was led by Dr. Gordon Winocur, senior scientist and vice-president of research at The Rotman Research Institute at Baycrest Centre for Geriatric Care and professor of Psychology at Trent University . It is published in the March 2005 issue of Nature Neuroscience and appears on the advance online publication February 20.

There is already a wealth of scientific evidence that implicates the hippocampus as critical for learning and retrieving new spatial memories and for navigation. Individuals with damage to this area from stroke or head injury often have extreme difficulty learning new spatial information in their environment. Yet, remarkably, they can retain accurate spatial memories of familiar environments that were acquired pre-injury, such as old neighbourhoods that they have lived in.

In the Rotman-Trent University study, researchers designed a “rat village” modeled after a human neighbourhood to see if animals who have extensive experience in an environment would, like humans, also retain those spatial memories after a hippocampus injury. The rat village was constructed with different routes and pathways, some of which ended at reward compartments with food and water. Rats were divided into three groups: those who were reared in the village for three months (extensive experience in a spatial environment); those who did not live in the village but received some exposure to it with the first group of rats in training exercises to learn how to navigate pathways to reward compartments (less experience); and those who had no exposure to the village.

After a three-month period, all three groups of rats underwent surgery to have lesions made in their hippocampus. They then underwent navigational and spatial memory testing in the village. Rats who had the advantage of three months of rearing in the village, in contrast to the other two groups of rats, found the appropriate reward compartments efficiently from the beginning.

“Our results demonstrate, for the first time, an important parallel between humans and rats with hippocampal lesions in the retention of pre-morbidly acquired spatial memories of a familiar environment, and point to similar underlying mechanisms in both cases,” says Dr. Winocur.

“This research emphasizes that even with severe damage to a structure critical for memory – the hippocampus -- other forms of memory are still present and likely supported by other regions of the brain.”

Dr. Winocur says the findings have implications for developing future therapeutic strategies based on supporting preserved cognitive functions and helping the brain injured regain some degree of independence.

The study was supported by a Science and Engineering Research Canada grant .