Wall collision warning | How does the brain rhythm bring us a sense of boundary?

Original author: Hugo J.
Spiers when we are close to the border (such as walls) or witnessed others close to the border, neuronal activity in the brain's medial temporal lobe will oscillate, encoded information we near the border.

Being close to a cliff can make people nervous, and watching others do it can also make us uneasy.

The brain’s ability to process such boundaries is very important.
It not only helps us avoid danger, but also helps us in daily navigation, because dividing the boundaries of space can help us locate resources.

It's like going through mountains and ridges, although it is dangerous, but it can take us to find food and partners.

So, how does our brain record this information? Stangl et al.
[1] published an article in "Nature" and pointed out that when people are close to the boundary, the rhythm of specific frequency of EEG will increase; when people see others close to the boundary, this rhythm will also appear in the brain.

Source: Pixabay Our navigation ability depends on some areas of the medial temporal lobe (MTL) of the brain, such as the entorhinal cortex and hippocampus [2].

Neurons in these areas will provide an internal signal, similar to the sign showing "your location" on the map [2], and other brain areas will associate this experience with space (for example, "Never return to this bad bar" ').

Some of these neurons can also specifically signal when we are close to the border [3,4].

Since it is difficult to record neuronal activity in humans when they are awake and active, our understanding of how the brain represents boundaries mainly comes from rodents.

For rats running around, their neuron activity will also produce theta oscillations when they send out boundary signals—theta oscillations are a kind of fluctuations in the overall electrical activity of the brain, caused by the joint activities of many neurons.

The frequency of theta oscillation is between 8 and 12 Hz [5].

For the human body, researchers have gained some insights by implanting electrodes into the medial temporal lobe of epilepsy patients who are waiting for neurosurgery.
The neuronal activity recorded by these electrodes can be processed to explain the epileptic discharge and reveal the deep structure of the brain.
The activity pattern of neurons.

For example, experiments that allow sitting people to navigate in a virtual environment show that when the human brain encodes position information close to the boundary, the theta oscillations generated by the medial temporal lobe will increase [6].

However, researchers have not been clear whether this activity also occurs when walking.

Stangl et al.
used a wireless recording system to overcome the difficulty of tracking a moving human body [7].

Subjects wearing this wireless device must alternately perform two activities: one is to walk to an unmarked target in the room, and the other is to walk to a visible target on the wall of the room (Figure 1a).

Participants are optimistic about the location of unmarked targets in the exploration phase, and then they have to remember where these marks are in the experiment.

Figure 1 | The same pattern of neuron activity between walkers and observers.

a, Stangl et al.
[1] designed an experiment in which one person was to explore in the room while the other was watching.

The walker remembers the target location at the beginning of the exploration phase, and then the target location will be hidden.
The walker needs to walk to the original location based on memory, and then walk to the location where the visible target is marked on the wall.

(For simplicity, each of these two goals is drawn in the figure, but there are actually more than one in the experiment).

The dashed line serves as a limit.
Crossing the dashed line is regarded as the pedestrian approaching the wall for analysis.
The arrows indicate different stages of walking (for example, the black arrow indicates that the pedestrian is approaching an invisible target and approaching the wall).

b.
The author analyzed the electrical activity of the medial temporal lobe (MTL) of the walker and the observer during this period, and found that when the walker navigates to an invisible target, there will be a strong oscillation pattern of brain electrical activity, also called theta Oscillate, but only if the pedestrian is also near the wall.

When the pedestrian navigates to a visible target, this oscillation is very weak.

Observers also showed the same pattern of activity, indicating that theta oscillation is part of our internal representation of space, and this internal representation can help us locate others.

When walkers approach an unmarked target, the theta oscillation of the medial temporal lobe increases as they approach the wall.

This change is consistent across all walkers and will persist when approaching or away from the wall.

It is worth noting that this oscillation is significantly weakened when the walker only walks towards the visible target on the wall, indicating that when people need to locate the target by memory, the theta oscillation related to the boundary is also the strongest (Figure 1b).

The experimental evidence that the medial temporal lobe of the human brain encodes boundary information when walking is exciting, because our daily navigation mainly occurs during walking.

Since allowing participants to walk will present additional challenges to the experiment, few studies have explored the neural dynamics behind this behavior.

Many other variables related to self-motion (such as speed) will also change according to the boundary distance, so we cannot be sure that the experimental results are indeed caused by the boundary.

To this end, Stangl and his colleagues included these indicators in the analysis, and then found that the changes in theta oscillations associated with the boundary seemed to have nothing to do with these variables, and also have nothing to do with the eye movement indicators.

However, some non-specific variables related to walking can also lead to the above results.

Stangl et al.
used the next experiment to answer this question.

The author asked other people to observe other people performing these tasks and recorded their neural activity.

This key experiment showed that the theta oscillation of the medial temporal lobe would also increase when watching others approach the wall.

So, whether you are approaching a cliff or watching your friend do it, the theta oscillation of your medial temporal lobe may increase.

Since the same reaction is observed in the observer and the walker, it seems to be said that the theta oscillation is indeed related to the internal representation of the space, rather than only related to visual input or automotion.

The discovery that the structure of the medial temporal lobe of the human brain can encode information about others is consistent with the evidence that rat and bat neurons can encode information about the location of other animals [8,9].

Broadly speaking, this discovery echoes the view that there is a "mirror" encoding of observations and actions [10].

There is another key question, why does theta oscillation increase near the boundary? Stangl et al.
believe that this may be due to the need for the entire brain neural network to integrate information when navigating.

However, we do not know why the need for such integration near the border will be greater.

Perhaps, when people are closer to the wall, they can more accurately infer where they are, and the increase in accuracy will lead to an increase in theta oscillation.

More experiments are still needed to verify this possibility, and why researchers have not reported this result in rodents so far.

One explanation for this is the design of animal experiments, or self-motion has a dominant effect on the theta oscillations of rodents [2].

The study by Stangl et al.
also raises a bigger question: How does our brain track the location of other people in space? Current models mainly focus on how self-positioning is constructed [2], but how visual input is used to position other things is also an exciting research area.

Stangl and others asked some participants to sit and watch others navigate.

But in terms of daily life, we usually watch while walking.

How do we integrate the location of ourselves and multiple other things? The brain seems to construct different maps when locating ourselves, our friends, and enemies, and connect these maps with more abstract social networks and knowledge system maps [11].

Some species have adapted to collective hunting, such as killer whales, wolves, and chimpanzees [12].

We don't know how their brains coordinate this behavior, but for now, the theta rhythm of the medial temporal lobe may be involved.

Thanks to Stangl and others who have crossed the technological cliffs, we can look forward to more exciting discoveries in the future.

168–170 (2020).
12.
Krause, J.
& Ruxton, G.
Living in Groups (Oxford Univ.
Press, 2002).
The original article was published under the heading Brain rhythms that help us to detect borders on December 23, 2020 On the News and Views section of "Nature" © naturedoi: 10.
1038/d41586-020-03576-8 Click to read the original text to view the English original text Click to read the popular article The mother’s intestinal flora supports the baby’s brain development Soul torture: created by the laboratory Will the brain be conscious? Nature Research Scientific Research Service Click on the picture to read the copyright statement: This article is translated by Springer Nature Shanghai Office. The content in Chinese is for reference only, and the original English version shall prevail for all content.