People with amnesia cannot remember events from their past
Amnesia patients struggle to imagine new and future experiences as well as being unable to recall events from their past, a study has shown.
UK researchers said the results showed those suffering from amnesia were "forced to live in the present".
People with amnesia could not imagine specific situations or see themselves going to future events such as a party.
The findings are published in the Proceedings of the National Academy of Sciences.
Experts said the results overturned current thinking on how memory works.
Study leader Dr Eleanor Maguire, cognitive neuroscientist at the Wellcome Trust Centre for Neuroimaging in London, said they were surprised to find that no-one had looked into whether amnesia patients could imagine future events.
They asked five patients with amnesia and 10 controls to imagine and describe in detail seven common settings such as a beach or a pub and three possible future events such as Christmas or a future meeting with a friend.
Participants were specifically asked to imagine something new and not something they had experienced previously.
Those with amnesia could not imagine plausible future events or general fictitious experiences.
They could describe separate images, but could not visualise the whole experience in their mind.
Dr Maguire explained that the role of the hippocampus, the part of the brain which is commonly damaged in amnesia, in processing memory seems to be much broader than is generally thought.
The findings suggest the hippocampus is involved in reliving past memories but also in supporting the ability to imagine any kind of experience, including possible future events.
"If you think about any personally significant event it always happens somewhere, there's always a spatial context so what we're suggesting is that the spatial context is the scaffolding around which memories are produced - the background into which the details are dropped," said Dr Maguire.
"People with damage to the hippocampus are forced to live in the present," she added.
Although it is possible that past memories are needed to imagine future events, the team said this was an unlikely explanation for the results.
"This has certainly given us some interesting new insights into how memory works," she said.
Dr Narender Ramnani, reader in cognitive neuroscience at the Royal Holloway University of London, said the findings overturned the world view of what the hippocampus is about - namely reliving past experiences.
"Memories are there to help is use past events to shape future events or future plans.
"One of the most interesting findings is the spatial context. It's not just being in a particular space, what also matters is the imagining of a particular space."
He added that the findings would help psychiatrists predict what problems people with amnesia may encounter in everyday life.