How Brain Predicts? Using Place cells And Brain Waves

Whether we realize it or not, we are in the middle of making decisions every moment. From what clothes to wear, what to eat and how to spend the weekend, to which pen to hold with your hand, do you want to adjust your center of gravity to make yourself more comfortable ... Even for the most trivial decisions, our brains will Choose carefully in the series "if" and weigh every possible future. Even if you make seemingly unconscious choices, such as avoiding a speeding vehicle, the brain makes predictions based on past experience to guide behavior. In an article published in Cell in January 2020, researchers at the University of California, San Francisco (UCSF) peeped into the brains of rats at the moment they made decisions, observing neurons quickly comparing the options in front of them. The mechanisms they describe may not only apply to specific decision-making behaviors, but they may also be involved when animals are creative and conceive more abstract possibilities.

Under the leadership of neuroscientist Loren Frank of the University of California, San Francisco, his research team studied the hippocampus brain area, which is shaped like the hippocampus and is related to spatial positioning, storage, and memory retrieval. They paid special attention to neurons called Place Cells, because when animals move in space, these cells, called the "GPS of the brain", can depict the animal's position in the brain. Studies have shown that when animals move in the environment, the cells in the location will quickly discharge in sequence.

This electrical activity not only reflects the actual position of the animal but also corresponds to the movement of the animal's front and back positions: in the order of space, the cells discharge from the back of the animal to the front of the animal in sequence as if scanning a spatial trajectory. (Studies have shown that these are moved forward or reward also contains a target location-related information) and the nerve activity pattern is referred to the period [theta] (Theta Cycles, also known as [theta] oscillations, brain waves, etc). In the rat brain, it repeats about eight times per second, characterizing them with constantly updated path information. Frank and his team found that when an animal is about to take action, the neural activity related to the θ cycle will alternately show different potential paths-not only to make predictions about the future, but also a response  in a high-speed.

Alternative scenarios in brain waves

The researchers trained the rats to choose different routes in the W-shaped maze, and simultaneously recorded the electrical activity of the cells at their locations. The rats ran through the passage in the middle of the maze and then turned left or right. However, when they were about to decide which direction to turn, the researchers noticed the weirdness of the cell activity in the rat's position. These rats are in the channel in the center of the maze. Some cells discharge when they are about to turn left, while others discharge when they are about to turning right. Logically, because the common activity of these cells reflects the animal's current position, both cells should discharge at the same time as the rat approaches the turning point. But this is not the case. In fact, these two cells fire alternately. It's like before the animals decide to take a certain path, their hippocampus alternately handles the choice of "left" or "right" and keeps both path independent. "The brain tries to separate them," Frank said. "The question is why the brain does this."

When the rat decides which direction to turn, the cells in its two locations in the brain do not fire at the same time, but alternately. Source: Quanta Magazine

A neuroscientist at the University of Minnesota's David Reddish and the late Adam Johnson have had similar findings. The animal looking for direction in the maze, place cells with potential to scan back and forth. Probably, but these activity changes seem to be related to more thoughtful behavior. The two researchers did not study further, and the neuron's representation of "left and right choice" appeared randomly or in an orderly manner. The difference is that the "left-right choice" phenomenon discovered by Frank's group precisely coincides with each θ cycle. The hippocampus signals the left-turn signal in one θ cycle, and then converts to the right-turn signal in the next cycle. Although these two signals are not always perfectly converted to each other in the experiment, occasionally a certain signal will last for several cycles. But the overall structure of the signal is irrefutable. Each cycle lasting 125 milliseconds seems to divide the brain's different assumptions about the future into a continuous and stable overall structure.

"The most amazing thing is the regularity. It's really amazing." Neuroscientist György Buzsáki of New York University School of Medicine commented, "The decision of each cycle and representation is One-to-one: one period signifies a left turn, another period signifies a right turn, and the left and right alternate. " He believes that the advantage of this highly structured arrangement may be that each prediction is ordered with the same probability test. Frank and colleagues further studied the neural activity of the θ cycle and found that the beginning of each cycle is related to the current position of the rat, and then characterize the choice of left or right turn. The overall structure looks like this: the current position, the possibility of turning left, the current position, the possibility of turning right, and so on.

Researchers are exploring the mechanisms that cause the observed alternating patterns and how this activity affects other parts of the brain in the decision-making process. They are also conducting labyrinth experiments involving more than two possible choices. Although rodents have different brain rhythms than humans, the researchers hope their findings will be equally applicable to other species. Kay said: "It's interesting to think about it, we just took a small first step on the precise time scale of understanding cognition and imagination."

Reference: https://www.quantamagazine.org/in-brain-waves-scientists-see-neurons-juggle-possible-futures-20200224/