The science of when: How our brain records time
Comment notre cerveau perçoit-il le temps ?
Comment arrivons-nous à resituer telle ou telle période de notre vie ? Pourquoi avons-nous tendance à confondre les jours lorsque ces derniers sont monotones ? Notre cerveau peut-il être littéralement « marqué » par un événement ? Une équipe de scientifiques a réussi à observer la manière dont nous percevons le temps. Explications avec The Independent.
In a new study, a research team based in Dallas reported the first strong evidence to date of so-called “time cells” in the human brain. The finding was not unexpected: in recent years, several research groups have isolated neurons in rodents that track time intervals. It’s where the scientists look for these cells, and how they identified them, that provide some insight into the subjective experiences of time.
2. “The first thing to say is that, strictly speaking, there are no such things as ‘time cells’ in the brain,” says Gyorgy Buzsaki, a neuroscientist at New York University. “There is no neural clock. What happens in the brain is neurons change in response to other neurons.” He adds: “Having said that, it’s a useful concept to talk about how this neural substrate represents the passage of what we call time.” 3. In the new study, a team led by Dr Bradley Lega, a neurosurgeon at University of Texas Southwestern Medical Centre, analysed the firing of cells in the medial temporal area, a region deep in the brain that is essential for memory formation and retrieval
ENCODING TIME
4. The team took recordings from 27 people with epilepsy, who were being monitored for surgery. These patients played computer games that test thinking and memory, while researchers watched what happened to the firing patterns of cells. In this experiment, the subjects tried to memorise lists of words, presented one at a time, a second or so apart. The subjects then had 30 seconds to freely recall as many as they could. 5. The researchers found that certain neurons fired during a specific window of the free-recall period. This firing was related only to time, not to anything else. And when those particular cells fired more precisely in a person’s temporal sweet-spot, he or she remembered words in close to the order in which they were originally presented.
6. “These cells are encoding information related to time, and this information is clearly important for memory,” Dr Lega says. There is no constant rhythm or background beat; the time signal is conjured as needed. “There’s no internal metronome, or clock,” he says. The time cells are “firing to support what you’re doing”. That is, time cells adjust to the demands being made on the brain, in real time, moment to moment.
“Strictly speaking, there are no such things as ‘time cells’ in the brain”