How do you know what is happening in front of you right now? How do you get a sense for what is going on?
I gave you a hint. You sense what is going on by using your senses to send input about the world to your brain. Once your brain receives sensory input, it translates and organizes this input. This process is called perception.
In my most recent set of videos, I have been discussing the science and theories that begin to explain perception. But this video is all about sensation. And I want to start by talking about the five main senses.
I say five main senses, because we have more than just five senses.
The Main Five (Aristotelian Senses)
It may surprise you to know that we have more than five senses. After all, how many senses did you learn about in school? Five!
For hundreds of years, scientists believed that humans have five senses that send input to the brain. The man behind this theory is not a neuroscientist, but a philosopher. That’s right. The five main senses are also known as the Aristotelian senses, because Aristotle is the big man behind this theory. He believed that each sense worked independently of each other.
These senses are:
As someone who uses all or most of these senses throughout the day, it makes sense (pun not intended) that these senses help us understand the world around us. And so these five senses became the core of studying how we use sensation and perception.
But there is a lot more to the senses than what Aristotle said. Before I move on, I want you to think about this question:
When you are looking directly at an object, how do you know that the object is three-dimensional?
Questions like this suggest that Aristotle was wrong when he said that all senses work independently. The blending of multiple senses is at play in this example. You may know that an object is three-dimensional because you have touched it or felt it. Other senses, including those outside of the five main senses, may be at play here as well.
Take wine tasting, or any kind of tasting. The smell of what you are about to taste is very important, at times just as important as the taste.
Keeping this work between the senses in mind, let’s talk about some additional senses that influence sensory and perception. Neuroscientists believe that we have up to at least 20 different senses that work to help us understand the world around us. I’ll explain just a few of the more important ones here.
Close your eyes. Picture your body as it is right now. What senses are you using?
Sure, you’re using touch. You may feel your hands on your desk or your butt on the seat. But you’re not using sight. You can practice this exercise without listening to anything. And you’re not using taste. Take a moment to picture your torso, the tip of your nose, or a part of the body that’s not making contact with anything. How do you know where that is?
The answer is one of the main senses discovered after Aristotle: proprioception.
Proprioception helps us sense where our body is in space and how it’s moving. (It’s also known as “spatial awareness” or the “kinesthetic sense.”) Have you ever moved up and down the stairs without looking at them? Thank your sense of proprioception. Have you ever done a “body scan” in a meditation class? That’s all proprioception.
People with poor proprioception are likely to bump into objects or be uncoordinated. You know when children go through growth spurts or puberty and can’t get a sense of how tall or large they are? They need to work on their proprioception.
What sense do you associate the ear with? Hearing! Within the ear are three different parts. One part is the cochlea, which contains a group of organs that help us hear. The other two parts contain organs including the utricle and saccule. These organs help us with our sense of balance.
Our sense of balance (also known as equilibrioception) keeps us upright. It also tells us which way is up, which way is down, left, right, etc.
The organs within the inner ear, along with the eyes and muscles throughout the body, all collect sensory input about the position and rotation of the body as it moves. If these organs are doing their job right, we stay upright and balanced.
I mentioned the utricle and saccule as two major organs within the inner ear that help us keep our sense of balance. These organs also help out with yet another sense - acceleration. When you are riding a roller coaster and you feel your body moving faster than usual, you can thank your inner ear and your sense of acceleration.
Close your eyes. How warm is it outside right now?
Yet another sense is the sense of temperature, or thermoception. Thermoception is a sense that is still relatively ambiguous to neuroscientists. Sure, we all know that if we walk outside and it’s 32 degrees, we are going to feel colder than if we walk outside and it’s 90 degrees. But why? And why are some people more likely to feel cold while others are more likely to feel hot in the same environment? Information about thermoceptic receptors and how they work with the brain is still relatively vague compared to our other senses.
Sometimes we experience pleasant touch. Other times, we experience pain. Pain, or nociception, is considered a sense all its own. Nociceptor cells are responsible for sensing threats to the body and sending that information to the brain. We have different types of nociceptor cells that cause different types of pain: the Alpha-Delta fibers produce a sharp, localized pain. The C fibers cause more burning or throbbing pain.
Both of these cells let the brain know that there is a possible danger to the area of the body where the threat was detected. In response, you might feel pain. This pain is a way of letting the body know that you should pay attention to the area of the body where you are feeling pain. That is why you might feel a mosquito bite on your leg even if you are not looking there. Or if you touch a hot pan, your hand feels hot and your body knows to remove your hand from that situation.
Pretty cool, right?
All of the senses that I just mentioned are external senses. They use input from the world outside our bodies. Other external senses include:
There are also internal senses that work like nociception. These internal senses send messages to and from the about what is happening inside the body.
Hunger and Other Internal Senses
One of these senses is hunger. Hunger is an internal sense, or interoception. The body senses an imbalance within the body and sends a message to the brain in order to correct that imbalance. In the case of hunger, the body is noticing an energy imbalance. You feel hungry because your body is telling you that you need more fuel.
These sensory receptors within the body may or may not be something that we notice with our conscious mind. Some sensory receptors, like the peripheral chemoreceptors, make us feel dizzy or suffocated if we are exposed to high levels of carbon dioxide. Others tell us when we are full, when we need to use the bathroom, or if we are about to vomit.
And then, there are senses that don’t have to do with any particular body part. Take our sense of time. “Chronoception” is the process in which the mind experiences and perceives the passing of time. Research shows that parts of the cerebral cortex and cerebellum play a role in this sense. Chronoception may also explain why people get that “2:30 feeling” and tend to get tired in the early afternoon, like clockwork.
A lot of these senses are basic concepts that you may not have understood to be senses before. Neuroscience is continuing to expand our ideas about senses and what constitutes as a sense. This research not only helps us understand how the brain and the body work, but also how we make sense of the world and our place in it.