One day not long ago a 27-year-old woman was brought to the
Tel Aviv Sourasky Medical Center, sleepy and confused. Fani Andelman, a neuropsychologist at the center, and colleagues gave the woman a battery of psychological tests to judge her state of mind. At first the woman seemed fine. She could see and speak clearly. She could understand the meaning of words and recall the faces of famous people. She could even solve logic puzzles, including a complex test that required her to plan several steps ahead. But her memory had holes. She could still remember recent events outside her own life, and she could tell Andelman details of her life up to 2004. Beyond that point, however, her autobiography was in tatters. The more doctors probed her so-called episodic memory—the sequential recollection of personal events from the past—the more upset she became. As for envisioning her personal future, that was a lost cause. Asked
what she thought she might be doing anytime beyond the next day, she couldn’t tell them anything at all.
The patient, Andelman realized, hadn’t just lost her past; she had lost her future as well. It was impossible for her to imagine traveling forward in time. During her examination, the woman offered an explanation for her absence of foresight. “I barely know where I am,” she said. “I don’t picture myself in the future. I don’t know what I’ll do when I get home. You need a base to build the future.”
The past and future may seem like different worlds, yet the two are intimately intertwined in our minds. In recent studies on mental time travel, neuroscientists found that we use many of the same regions of the brain to remember the past as we do to envision our future lives. In fact, our need for foresight may explain why we can form memories in the first place. They are indeed “a base to build the future.” And together, our senses of past and future may be crucial to our species’ success.
Endel Tulving, a neuroscientist at the University of Toronto, first proposed a link between memory and foresight in 1985. It had occurred to him as he was examining a brain-injured patient. “N.N.,” as the man was known, still had memories of basic facts. He could explain how to make a long-distance call and draw the Statue of Liberty. But he could not recall a single event from his own life. In other words, he had lost his episodic memory. Tulving and his colleagues then discovered that N.N. could not imagine the future. “What will you be doing tomorrow?” Tulving asked him during one interview. After 15 seconds of silence, N.N. smiled faintly. “I don’t know,” he said.
“Do you remember the question?” Tulving asked.
“About what I’ll be doing tomorrow?” N.N. replied.
“Yes. How would you describe your state of mind when you try to think about it?”
N.N. paused for a few more seconds. “Blank, I guess,” he said. The very concept of the future, seemed meaningless to N.N. “It’s like being in a room with nothing there and having a guy tell you to go find a chair,” he explained.
On the basis of his study of N.N., Tulving proposed that projecting ourselves into the future requires the same brain circuitry we use to remember ourselves in the past. Over the past decade, as scientists have begun to use fMRI scanners to probe the activity of the brain, they have found support for his hypothesis. Last year, for example, Tulving and his colleagues had volunteers lie in an fMRI scanner and imagine themselves in the past, present, and future. The researchers saw a number of regions become active in the brains of the volunteers while thinking of the past and future, but not the present.
Studies on children also lend support to Tulving’s time travel hypothesis. Previous work had shown that around the age of 4, children start to develop a strong episodic memory. Thomas Suddendorf, a psychologist at the University of Queensland in Australia, designed a series of experiments to see if foresight develops with the same timing. In one experiment, published earlier this year, he showed 3- and 4-year-olds a box with a triangular hole on one side and demonstrated how to open it with a triangular key. He then swapped the box for one equipped with a square lock and gave the children three different keys. Most of the 96 subjects correctly picked the square key, regardless of their age.
Then Suddendorf ran the experiment again, but with a twist to test the children’s foresight. Instead of choosing a key for the square lock right away, the kids were first taken to another room to play for 15 minutes; only after that were they offered a choice of keys, which they had to take back to the room with the box. The children had to anticipate what would happen when they tried to unlock it. This time Suddendorf found a sharp break between the 3-year-olds and the 4-year-olds. The younger kids were just as likely to pick one of the wrong keys as the right one. The older kids did much better—probably because, with more developed episodic memories, they remembered the square lock and used that knowledge to project into a future in which only a square key would unlock the box.