Brain damage not just erases one’s memories, in some cases it may also create a false sense of familiarity with the new objects, a new study has claimed.
Researchers from the University of Cambridge, London, who made this surprising discovery said it could help explain similar memory problems for humans suffering from amnesia or Alzheimer’s disease. Both of those conditions can damage a specific part of the brain called the perirhinal cortex — a region buried in the middle part of the brain that helps form memories by sifting through incoming information from the senses and building a complex picture of an object.
“The perirhinal cortex is one of the first regions that is affected in Alzheimer’s disease, and it is very often damaged in cases of amnesia, so specific damage in this region is highly relevant to both of these conditions,” researcher Lisa Saksida, a psychologist at Cambridge, told LiveScience.
Damage in that part of the brain disrupts the ability to form memories based on complex, detailed representations of objects seen in the real world. That means the brain must rely instead upon simpler features that commonly appear across many objects.
“The remaining representations of simpler features of objects are relatively easily confused, and as a result, false memories are generated,” Saksida explained.
The first clue about false memories came from a computer simulation
that allowed researchers to test the effects of virtual brain damage.
That simulation predicted that animals that suffered damage to the perirhinal cortex should see novel objects as familiar.
“The prediction was quite counterintuitive, and we were indeed surprised, so we thought we’d figure out a way to test it,” Saksida said.
To further test this, Saksida and her colleagues carried out a series of experiments involving both normal mice and those that had been selectively brain-damaged through surgery as part of the experiment.
The researchers first gave the rats three minutes to familiarise themselves with a specific “junk object” — a small, complex and colourful object similar to a small garden gnome or plastic toy train.
Next, they held the rats in a separate cage environment for an hour before releasing the rats into an environment where they encountered either the old object or a new object.
Normal rats spent more time exploring the new objects, and less time with the old familiar object. But the brain-damaged rats spent less time exploring the new object — a sign that they treated the new object as if it were familiar, the team detailed in the journal Science. If the rats had simply forgotten about having encountered the old object, they would have spent more time exploring both the old and new objects, said the researchers. The findings support a 10-year-old theory of cognition.