Your brain is made up of billions of neurons that are constantly firing electrical signals back and forth to tell you what to do, what to think, and how to feel.

But your body actually has a second brain that controls you much more than you might realise - and most people have no idea it exists.

As this episode of AsapSCIENCE explains, one of the main ways our brain communicates with the rest of our body is via the vagus nerve, which passes messages to the vocal chords, heart, lungs, and the digestive tract.

But researchers have also discovered that within the enteric nervous system - the extensive mesh-like network of neurons that controls your digestive tract - the messages are going the other way, too.

In fact, 80 to 90 percent of the nerve fibres in the enteric nervous system are going from the gut to the brain. And when the vagus nerve is cut, the enteric system doesn't need the brain at all.

In other words, your digestive system is your second brain, and it controls you far more than you realise.

I know what you're thinking here - just because the gut can pass messages back to the brain, doesn't mean it's in control. But it turns out our digestive system also influences our choices on a daily basis.

This is most likely because back when our ancestors were living as hunter gatherers, some of the most important life-or-death choices they'd have to make were based on food: would eating a berry provide enough energy to get through the day? Would it be poisonous?

Because of this, from an evolutionary perspective, it makes sense to have a direct line of communication between the gut and the brain.

But even today, it's incredibly influential.

Not only has research shown that our gut bacteria can manipulate our food cravings and behaviour in order to ensure their own survival (you can blame them on your junk food obsession), but the colonies in our digestive system also affect our mood.

Studies suggest that people with healthy and diverse gut microbiomes are less likely to be depressed or anxious.

And, in mice, researchers have shown that those that grow up in sterile environments - where no bacteria colonise their guts - display social traits similar to those in humans on the autism spectrum. When these mice were fed probiotics, their symptoms were alleviated.

This kind of effect has been seen in early studies in humans too, leading many scientists to believe that one of the primary functions of gut bacteria is actually to promote social behaviours and ensure the survival of the species through reproduction - but we'll let the AsapSCIENCE video above explain that.

In some ways, it seems like our second brain is even more influential than our logical thought. And, great, now we can't stop second-guessing which brain is making us do everything. Sometimes science is so creepy.