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In this article:
- The somatosensory cortex is the part of the brain responsible for processing the signals sent from the sensors in the rest of your body.
- In addition to the five main senses that we commonly think of, researchers are now realizing that it’s processing other sensory input we never knew we had.
- All told, your somatosensory cortex is processing anywhere from 15 to 30 senses.
- In some cases, those extra senses are a matter of one sense (like touch or sight) actually being made up of a handful of distinct senses.
- In other cases, researchers are discovering entirely new senses like the ability to detect magnetic fields or sense the passage of time.
Your somatosensory cortex is a region of your brain that processes all the signals that sensors around your body send to your brain to tell it when, where, and how you are. While we often focus on the dominant five: sight, sound, smell, taste, and touch — scientists are discovering that humans actually have somewhere between 15 and 30 senses.
Some of those, as you’ll see below, are just the discovery that the dominant senses we think of as a single sense are actually the combined effort of multiple different senses.
When using sight, for example, you’re actually using at least two different senses: the sense of brightness levels and the sense of colors. That’s why people who are colorblind can still see and navigate the world using sight.
Others are entirely separate, previously taken for granted senses like our ability to sense the magnetic field that surrounds us — which is why we can still tell when we’re upright or upside down, even if we’re floating underwater.
The Lesser-Known Sense of Our Somatosensory Cortex
The Many Sides of Touch
The sense of touch is actually a bundle of dozens of different kinds of sensors that send signals to the somatosensory cortex.
Some sense heat. Some sense cold. Some sense pain. Some sense itchiness. Some sense pressure. The more research that is done in this field, the more scientists are realizing just how specialized these many sensors that we lump under “touch” are.
There are up to six sensors for detecting temperature, for example, each tuned into a different temperature range running from freezing cold to boiling hot.
Even the sense of pressure is actually detected by at least two different sensors. One detects light pressure and the other detects harder pressure. So that gentle breeze brushing against your skin is detected by one sense while that bear hug from your best friend you haven’t seen since before the pandemic is detected by another.
This is why people with touch-related sensory issues can have such seemingly bizarre specifications about what precisely bothers them.
Some might be hypersensitive to hard pressure, finding even a firm handshake to feel like bone-crushing agony, and only able to tolerate the gentlest of caresses. Others are the opposite: a gentle caress feels excruciating, but a firm squeeze feels fine.
It all comes down to which specific touch sensors are involved in their sensory issues.
Magnetoception
Dozens of species, ranging from honeybees to whales, rely on their sense of the magnetic field that surrounds the planet to navigate and orient themselves. Most famously, bats, which are blind, use a combination of echolocation and magnetoception to fly through the air without crashing into anything.
Until very recently, scientists assumed that humans were excluded from this super cool group of species that use their magnetoception to move through the world.
But recent research is starting to prove that our somatosensory cortex does, indeed, sense the magnetic field. While we’re nowhere near as attuned to it as bats, we do have sensors, most likely in our inner ears that detect the magnetic field.
These are sensitive enough to sense altitude, which helps us figure out if we’re upright or upside down, even underwater. It also helps us balance and develop a sense of direction. By detecting changes in our orientation to the magnetic field, we can sense whether we’re going straight ahead or veering off course.
This is why inner ear damage can disrupt your sense of balance, your sense of direction, and give you a feeling of vertigo (the feeling that you’re falling, being pulled strongly in one direction, or heavily weighed down even when you’re just standing still).
Proprioception
Sensors in our muscles and joints send signals to the somatosensory cortex to help it keep track of where our limbs are in space and how much tension is in them, an ability known as proprioception. It’s why you can still touch your fingertips together even with your eyes closed.
It’s also why those same hands you just pried open a frozen-shut car door with can immediately pick up a glass of water without crushing it. The somatosensory cortex uses proprioception to tell them how much pressure to apply in each scenario.
When certain brain injuries or muscular disorders like Multiple Sclerosis or Lou Gehrig’s Disease (ALS) disrupt this sense, people tend to struggle with coordinating movement and walking straight, especially on uneven surfaces or stairs.
This disrupted proprioception can also cause problems with moderating your strength — such as applying too much pressure to pick up a delicate flower or too little pressure to pick up a cinderblock.
Chronoception
This sense is still a matter of some debate because, while researchers aren’t yet sure what specific sensors are at work or what specific input they’re picking up on, there is clear evidence that humans have a remarkably accurate sense of the passage of time.
If you’ve ever tried to estimate the time and found that you were right on the dot (or pretty close), that was probably your chronoception at work. If you’ve ever woken up just minutes before your alarm was set to go off, that’s your chronoception at work.
It’s likely a combination of multiple sensors that your somatosensory cortex is using, including:
- UV radiation sensors in our skin that detect UV wavelengths not visible to the eye to help regulate our circadian rhythm (our roughly 24-hour sleep-wake cycle).
- The visceral nervous system which senses pain, reflexes, contractions, and stretching in our organs, glands, and blood vessels to help regulate our ultradian rhythm (shorter 90-120 minute cycles that dictate hormone secretions, blood circulation, and other shorter processes).
- Ganglion cells that sense changes in the duration of time that shorter wavelength light (blue light) is present in order to sense time of year and seasonal shifts — more blue light means longer summer days, less means darker winter days. This helps regulate our infradian rhythms (multi-day cycles that dictate longer processes like the menstrual cycle, hair growth, or seasonal depression).
Because of all these sensory inputs to our somatosensory cortex, we’re able to act as a kind of walking, fleshy clock that can reliably tell what time it is (both the time of year and time of day) as well as reasonably estimate how long we’ve spent on a particular task — all without checking our phone.
One reason researchers know that our body is capable of chronoception is because certain disorders and diseases can disrupt it.
People with attention-deficit/hyperactivity disorder (ADHD), for example, have been found to be remarkably bad at accurately sensing time. It’s a frustrating symptom that many with the disorder refer to as “time blindness” but the technical term is dyschronometria.
Typically, people with this condition vastly underestimate how much time has passed but it can also cause them to overestimate.
This time blindness is one of the factors behind many of the symptoms associated with the disorder including procrastination, chronic lateness, and forgetfulness. It’s not that they’re consciously delaying tasks.
It’s that lack of ability to sense the passage of time without the aid of an elaborate system of alarm clocks and timers that makes it so difficult to determine when to start a task or how to best schedule tasks into your 24-hour day.
In addition to poor time management, dyschronometria can also be disorienting. Imagine being convinced that only five minutes has passed since you started googling how to hone your magnetoception, only to look at the clock and see that it’s actually been five hours. Now imagine experiencing that kind of shock every day.
