How does the brain remember time?

If you want to retell what you did this morning, you might tell a scene like getting up, brushing your teeth, washing your face, getting dressed, eating breakfast, and maybe walking your dog. It’s easy to find out that when you recall and repeat the experience, you clearly remember the different times of each scene, such as brushing your teeth and then washing your face. You must brush your teeth and wash your face when you recall and repeat. Then do you know how the brain remembers the different times of doing these things? The answer lies in the hippocampus, the most important area of ​​brain memory.

Mysterious hippocampus

The hippocampus is usually considered to be the location of spatial location memory cells.

When we arrive at a specific location, some specific neuronal cells in the hippocampus, ie, the location cells, are activated, creating a map of the brain about the spatial location around the body. The activated cells are like markers, remembering the body. The specific location. The cells in the head of the hippocampus can distinguish the orientation of the head. When facing in different directions, different cells are excited. In a region of the hippocampus called the entorhinal cortex, another group of neuronal cells called grid cells respond to the distance you travel. The combination of these cells allows us to know where we are in space, how to find directions in a complex environment, and how far it takes to move from one place to another. Therefore, the hippocampus can also be said to be the “GPS” inside the brain, which is the main component of spatial memory.

Can the hippocampus only remember the spatial location? An operation seems to give scientists a different view of the hippocampus memory function.

On September 1, 1953, a neurosurgeist underwent an adventurous surgery: in order to treat patients with epilepsy, he removed the hippocampus and surrounding tissues in the patient’s brain. Surgery does reduce the frequency and intensity of the patient’s attack, but the patient’s memory has a big problem: he can no longer sort the memory. Whether it’s breakfast in the morning, recent headlines, or a stranger I just met a few minutes ago, he doesn’t repeat the chronological sequence of the scenes he experienced. Some scientists are excited about it: “Maybe, some cells in the hippocampus may be closely related to time memory.”

Time cells appear

In order to find cells in the hippocampus about time memory, some scientists have done an experiment in which electrodes are implanted into the hippocampus of mice and the neuronal cell discharge behavior is recorded. Then let the mouse run on a small treadmill, so that the position and behavior of the mouse remain the same, scientists can focus on the time-related neural signals. Whenever a mouse ran for 15 seconds, the scientist gave it a reward for food.

They found that after repeating the experiment over and over again, the mouse’s brain learned the 15 second interval between the tracking reward and the next reward. Neuronal cells form a special pattern of discharge – some neuronal cells signal at 1 second, and some neuronal cells signal at 2 seconds… until 15 seconds pass. Since these neurons emit signals at different points in time, by analyzing these signals, the mouse can know whether the time has passed by 1 second, 2 seconds, or 15 seconds.

When the scientists extended the time from 15 seconds to 30 seconds, the time points at which the neurons emitted the signal changed, and they produced a new discharge pattern to fill the new time interval, such as the original one second. The signal is now in units of 2 seconds. It’s like reprogramming neuronal cells so that they follow the same time scale. This research shows that we may also rely on this model to realize how much time has passed, just as drivers always know how long it takes for a yellow light to turn into a green light. Sometimes, they can even be accurate to a few o’clock. Seconds – this is because neuronal cells are programmed to discharge a signal every 0.1 seconds.

Another group of scientists found that in 300 hippocampal neuronal cells, about 100 neurons conform to this pattern of transmitting signals one after another at different time points. Moreover, when the situation is different, the number of neurons that continuously transmit signals is different, which indicates that there are many groups of cells in the hippocampus that respond to time. Different cell groups allow us to remember the different scenarios. time.

These neuronal cells that respond to time are aptly called “time cells” and are abundantly present in the hippocampus. What is their specific role?

Brain nerve clock

The clock is a device designed by humans to measure time. We coordinate our activities according to the time displayed by the clock, such as work, study or rest. Although the brain does not have a standard unit of minutes or hours like a clock, it has evolved a variety of biological clocks to sense time, such as the circadian clock, which allows us to adapt to the 24-hour day and night changes caused by the Earth’s rotation, and allows us to measure 24 hours duration. If it is some shorter time? For example 10 seconds? 20 seconds? At this time, time cells come in handy.

Time cells behave much like a timed stopwatch. The stopwatch starts timing when the button is pressed, and the time cells are timed by discharge. They are more flexible than the stopwatch, the stopwatch can only follow the 1 second timescale, and the time cells can be based on the time interval between two things (like 15 seconds and 30 seconds between the two rewards in the mouse experiment). Follow different time scales.

Time cells can well record the blank time between events and use continuous discharge to code how much time has elapsed. The electrical signal is like the “tick” of the clock, recording every second of the time. It can be said that the time cell is the nerve clock of the brain.

The brain is an important and extremely complex organ, and it is also the root of human wisdom, so cracking the secrets of the brain has always been the dream of scientists. The emergence of time cells has made people understand the way the brain timing works, and once again deepen the understanding of the mysterious brain. Human beings have taken a big step away from cracking the brain. This new way of working may create a new kind of artificial intelligence that gives artificial intelligence the flexibility to master time so that artificial intelligence can better serve humans.