How the Brain Performs “Mental Time Travel”
In Proust’s novel Recollection of Things Past, the distinctive smell of a lemon madeleine launches the narrator on a long, involved reminiscence of his past that fills seven chapters.
This literary example is an extreme instance of what neuroscientists term “mental time travel” – the recollection of memories so rich in detail regarding the time and place of an original experience that the sensation is much like traveling through time.
In a paper published February 18th 2015 in the Journal of Neuroscience, a team of scientists at Vanderbilt University in Nashville, Tennesee shed new light on how the brain processes these elaborate memories. A release from the university explains that by analyzing the brain activity of people performing a simple memory recollection task, the researchers found that they can use the activity patterns in a specific region of the brain to substantially improve their ability to predict the order in which the participants recall information that they have recently studied.
The release quotes study leader Assistant Professor of Psychology Sean Polyn as saying, “It’s extremely important that we understand what different brain regions are doing as we search through our memories. Diseases like Alzheimer’s and epilepsy are devastating to memory, and this information can help us develop treatments to preserve patients’ memories, and identify adverse effects that new psychotropic drugs may have on people’s memory.”
Scientists have known for some time that a portion of the brain called the medial temporal lobe plays a central role in memory because injuries to the MTL cause amnesia and other memory-related problems. However, they have not been able to answer the question: How does the brain control the fidelity of an individual memory?
Of course, not all memories are recalled equally. High fidelity Proustian memories are at one end of the spectrum. At the other are bits of information that a person remembers clearly, but in complete isolation, without any accompanying details. Polyn, working with doctoral students James Kragel and Neal Morton (who is now at the University of Texas, Austin), has developed a model that accounts for how the structures in the MTL support memory retrieval. They have found that the anterior region of the MTL signals that a memory is being retrieved, but doesn’t indicate how detailed it is. However, when the posterior region of the MTL becomes active it indicates that the person is experiencing a “time travel” memory accompanied by considerable detail.