Why do we rarely fall out of bed when we sleep? The reason is the mysterious "sixth sense"

When we sleep at night, we usually sleep upright.

It is also possible to sleep sideways.

Or something even stranger, sleeping sideways.

But no matter how we sleep, we rarely fall out of bed. Why is that?

First of all, it may be that your bed is really big, big enough that you can roll over several times without reaching the edge of the bed.

Or maybe your bed has rails around it, or you just sleep on the floor...

But if none of the above situations exist, then the real reason why you can't fall out of bed is because our body has a kind of "proprioception" ability.

More than two thousand years ago, Aristotle proposed that humans have five senses, namely vision, taste, smell, hearing, and touch .

Although various other sensory organs were discovered later, this ancient "saying" has been preserved to this day, and although these five "common" senses basically cover most situations in reality.

But experiments that guided blind people to move and observed their sensory systems showed that the body's sense of movement and posture depend on multiple types of receptors densely packed in muscles and tendons.

In 1906, Charles Sherrington coined the term "proprioception" for the sensory modality of these receptors, calling it his "mysterious sixth sense."

The function of proprioception is actually very similar to traditional sense.

Proprioceptors can accurately measure physical properties such as muscle length, tendon tension, angles of joint rotation, and internal pressure in our bodies.

The receptors transmit the collected signals through the afferent nerves to the parietal cortex of the brain through the spinal cord, and then the continuous signals are converted into dynamic sensory-motor maps of the human body.

That is, proprioceptors provide our brain with information about the body's physical properties, the instantaneous distribution of mass, and the power generated by muscle activity.

With this information, the brain can not only "guide" human movement, but also perceive the size and shape of objects (with touch) and measure the geometry of external space.

Therefore, the subjective body consciousness collected by proprioceptors provides the basis for our body to objectively understand the basic properties of the external world (space, time, weight, etc.).

So when we are awake, proprioception prevents us from falling and slipping;

When we sleep, it will help us adjust to a more comfortable sleeping position. It will also allow our bodies to become familiar with our position in the bed and determine the surrounding space, preventing us from falling off the bed while sleeping.

But when we are young, our proprioception doesn't work very well, which is why children sometimes fall out of bed.

As proprioception improves with age, older children and adults are less likely to fall out of bed.

Another one is our brain.

When we sleep, it seems that our tired bodies have completely "stopped working", but in fact our brains are still working tirelessly.

As early as the 1940s, scientists used electroencephalogram (EEG) devices to test the activity of our brains while we sleep. By gluing electrodes with small metal circles to our heads and eyes, they discovered that our bodies do not stop functioning when we sleep, but our brains and eyes are doing a lot of things.

The eyes make multiple slow, smooth side-to-side movements, which is something we cannot do when we are awake and is called "slow eye movements."

In addition, during the "REM sleep" stage, our eyeballs will move rapidly, just like when we are awake, which means that your eyes are "dreaming."

That's right, this is when you wake up and are able to recall your dreams during the night.

However, there is one thing that is not so "safe" about this stage, which is that it is easy to confuse dreams with reality, so at this time the proprioceptors will send signals to the brain to restrict our actions to reduce the possibility of us getting up or rolling out of bed.

But there is also a more special case called "rapid eye movement behavior disorder". A very small number of people with this disorder cannot receive signals from the proprioceptors in their brains, and then they will get out of bed by themselves to meet their needs in their dreams, which is a bit similar to sleepwalking.