How does the brain remember time?

   If you retell what you did this morning, you might tell the scene: getting up, brushing your teeth, washing your face, getting dressed, eating breakfast, and maybe walking your dog. You can easily find that when remembering and recounting this experience, you clearly remember the different times of each scene, for example, you brush your teeth before washing your face, and you must brush your teeth before washing and recalling your face. Do you know how the brain remembers different times when doing these things? The answer lies in the hippocampus, the most important area of ​​brain memory.
   Mysterious hippocampus
   hippocampus is generally considered to be located at a spatial position of the memory cell.
   When we reach a specific location, some specific neuron cells in the hippocampus, ie, location cells, will be activated, creating a map of the brain about the spatial location of the body itself. The activated cells are like markers. Specific location. The head direction cells in the hippocampus can identify the head orientation. When facing different directions, different cells are excited. In an area of ​​the hippocampus called the entorhinal cortex, another group of neurons 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 we need to go 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.
   Does the hippocampus only remember spatial locations? One surgery seems to give scientists other insights into the hippocampus’ memory function.
   On September 1, 1953, a neurosurgeon performed a risky operation: to treat patients with epilepsy, he removed the hippocampus and surrounding tissue from the patient’s brain. Surgery did reduce the frequency and intensity of the patient’s attacks, but the patient’s memory had a big problem: he could no longer sort the memory. Whether it’s breakfast in the morning, recent news headlines, or a stranger whom he just met a few minutes ago, he doesn’t retell the chronological sequence of the scenes he is going through. Some scientists are excited: “Maybe some cells in the hippocampus may be closely related to temporal memory.”
   Time cell emergence
   To find cells related to temporal memory in the hippocampus, some scientists performed an experiment in which electrodes were implanted into the hippocampus of mice to record the firing behavior of neurons. Then let the mice run on a mini-treadmill, which keeps the mouse’s position and behavior unchanged, and scientists can focus on time-related neural signals. Every time the mouse ran for 15 seconds, the scientist gave it a food reward.
   They found that after repeating the experiment over and over again, the rat’s brain learned to track the 15-second interval between the reward and the next reward. Neurons form a special firing pattern-some neurons emit a signal at 1 second, some neurons emit a signal at 2 seconds … until 15 seconds elapse. Since these neurons emit signals at different points in time, by analyzing these signals, mice can know whether the time has passed by 1 second, 2 seconds, or 15 seconds.
   When scientists extended 15 seconds to 30 seconds, the time point at which neurons emitted signals changed, and they created a new discharge pattern to fill new time intervals, such as the original emission in 1 second units. The signal is now in units of 2 seconds. It’s like reprogramming neurons to make them go on different time scales. This research shows that we may also rely on this model and realize how much time has passed, just as drivers always know how long it takes for the yellow light to turn green, and sometimes they can even be accurate to a few tenths Seconds-This is because neuron cells are programmed to emit a signal every 0.1 seconds.
   And another group of scientists found that out of 300 hippocampal neuron cells, about 100 neurons fit this pattern of emitting signals one after the other at different points in time. Moreover, when the situation is different, the neuron cell population that continuously emits signals is also different, which indicates that there are many groups of cells in the hippocampus that respond to time. Different cell populations allow us to remember what happened in different scenarios. time.
   These neuronal cells capable of responding to time are vividly called “time cells” and are abundant in the hippocampus. What is their specific role?
   Neural clock of the brain
   The clock is a device designed by humans to measure time. We will 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 biological clock, which allows us to adapt to the 24-hour diurnal changes caused by the rotation of the earth, and also allows us to measure 24 hours duration. What if it’s some shorter time? Like 10 seconds? 20 seconds? At this time, the time cell comes in handy.
   The time cell behaves much like a chronograph stopwatch. A stopwatch starts timing when a button is pressed, and a time cell counts by discharging. They are more flexible than stopwatches. Stopwatches can only go on a 1-second time scale, and time cells can be based on the time interval between two things (like 15 and 30 seconds between two rewards in a mouse experiment). Follow different time scales.
   Time cells can well record the blank time between events, and use continuous discharge to encode how much time has elapsed. The electrical signal is like a “tick” sound of the clock, recording every second of time passing. It can be said that the time cell is the neural clock of the brain.
   The brain is an important and extremely complex organ and the root of human intelligence, so it has always been the dream of scientists to crack the secrets of the brain. The emergence of time cells has made people understand how the brain’s timing works, and once again deepened their understanding of the mysterious brain. Humans have taken a big step away from cracking the brain. This new mode of operation may create a new type of artificial intelligence, so that artificial intelligence can also flexibly control time, so that artificial intelligence will better serve humanity.