Daydreaming is a critical component of conscious experience. The mind can perform mental time travel – it occasionally strays from the present moment, to recollect an experience from the near or distant past, or to imagine an event that has not yet taken place. We know that thinking about the future is dependant on memory, because patients with amnesia cannot imagine new experiences. It involves piecing together fragments of past experiences to generate a plausible simulation of what might happen. This may have been an important development in human evolution, as it enables us anticipate a likely outcome and to plan the best possible course of action.
Space and time are intimately linked in the mind, and this is reflected in our metaphors. We often say that we are thinking back to a past event, or looking forward to one that will take place in the future. But the mind and body are also closely linked: think about a past experience, and you might find yourself moving backwards. A new study suggests that this can be reversed, by showing that apparent motion can influence the direction of the mind’s wanderings. Thus, moving backwards could evoke long lost memories, while moving forward might make you think about the future.
FORMATION of a memory is widely believed to leave a ‘trace’ in the brain – a fleeting pattern of electrical activity which strengthens the connections within a widely distributed network of neurons, and which re-emerges when the memory is recalled. The concept of the memory trace was first proposed nearly a century ago, but the nature of the trace, its precise location in the brain and the underlying neural mechanisms all remain elusive. Researchers from University College London now report that functional magnetic resonance (fMRI) can be used to decode individual memory traces and to predict which of three recently encoded memories is being recalled.
The new study, led by Eleanor Maguire of the Wellcome Trust Centre for Neuroimaging, builds on earlier work which demonstrates that fMRI can be used to predict simple mental states from brain activity. Last year, Maguire and her colleagues showed that it is possible to predict an individual’s position in a virtual reality environment from patterns of activity in the hippocampus, and researchers from Vanderbilt University showed that activity in the visual cortex can be decoded to predict which image is being retained in working memory. Even more remarkably, Japanese researchers have reconstructed visual images from brain activity, including novel ones that their participants had never seen before.