Our body apparently plays a crucial role in how we remember things and our memory may fail us if we "step out" of our body, findings of a new study suggest.
In the study "Out-of-body-induced hippocampal amnesia" published in Proceedings of the National Academy of Sciences, researchers had 84 student-volunteers wear goggles and headphones so they could see and hear through a camera and microphone placed elsewhere in the room.
The volunteers were then interviewed by a Swedish actor, who acted as an overly eccentric professor, for information they had studied. The eccentric nature of the interviewer was intended to make the questioning session memorable.
The first group of the volunteers then underwent two sessions of questioning looking through goggles to create a first-person perspective. Volunteers in the second group also had two questioning sessions but were given an out-of-body illusion by getting them to see themselves through virtual reality goggles similar to looking at themselves in the mirror.
The researchers found that the volunteers in the second group who were virtually shifted out of their body had more difficulty remembering the details of the event one week later than those in the second group.
"It is already evident that people who have suffered psychiatric conditions in which they felt that they were not in their own body have fragmentary memories of what actually occurred," said study author Loretxu Bergouignan, of the Department of Neuroscience of Karolinska Institutet in Stockholm, Sweden. "We believe that this new knowledge may be important for future research on memory disorders in a number of psychiatric conditions such as post-traumatic stress disorder, borderline personality disorder and certain psychoses where patients have dissociative experiences."
The functional magnetic resonance imaging (fMRI) scans also showed that the out-of-body volunteers relied less on their brain's hippocampus, the part of the brain responsible for memory forming, organizing, and storing.
"When they tried to remember what happened during the interrogations experienced out-of-body, activity in the hippocampus was eliminated, unlike when they remembered the other situations," said study author Henrik Ehrsson, also from the Department of Neuroscience of Karolinska Institutet. "However, we could see activity in the frontal lobe cortex, so they were really making an effort to remember."
The researchers said their findings show an association between body experience and memory as the brain creates experiences based on information from the different senses.
"These findings establish that hippocampus-based episodic memory depends on the perception of the world from within one's own body, and that a dissociative experience during encoding blocks the memory-forming mechanism," the researchers wrote.
