Old age not only steals a person's most memorable memories, it also diminishes his ability to imagine things, reveals a new study.
The study, led by Dan Schacter of Harvard University, supports the 'prospective brain' hypothesis, the idea that imagining the future and remembering the past relies on the same neural machinery.
"One implication of this study is that imagining is quite closely related to, and dependent on, remembering, perhaps more so than we previously realized," Nature quoted Schacter, as saying.
In the study, the researchers asked groups of young and old participants, with average ages of 25 and 72, respectively, to recount a personal episode from their past or imagine a personal experience in their future in response to cue words.
The responses of the participants were categorized as either 'internal' or 'external'.
Internal memories are similar to scenes from a movie: they contain specific subjects and take place in particular settings and time periods. External memories consist mostly of general facts about the world, such as 'the sky is blue'.
The results showed that the past accounts of the older participants' tales contained fewer, and less detailed, internal memories than those of the younger group. This deficit also extended to their future imaginings.
Brian Levine, a neuroscientist at the University of Toronto in Canada, is convinced that the data show a real decline in personal future imaginings.
"I think that methodologically they have ruled out the other possible explanations," Levine says.
The researchers contemplate that personal memories are particularly susceptible to ageing because they rely heavily on 'relational processing', the ability to mentally summon and join unique pieces of information, such as where and when an experience occurred.
"Once things in the past are finished, there's nothing you can do about them," Levine said.
The study is published in the journal Psychological Science 1.