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 one 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.
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 Many Sides of Touch
The sense of touch is actually a bundle of dozens of different kinds of sensors. Some sense heat. Some sense cold. Some sense pain. Some sense itchiness. Some sense pressure. The more research 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 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 sense.
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 be agonizing and only able to tolerate the gentlest of caresses. Others are the opposite, a gentle caress feels excruciating, but a firm squeeze feels fine.
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 we do, 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).
Sensors in our muscles and joints 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. They know how much pressure to apply because of proprioception.
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.
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, including:
- UV radiation sensors in our skin which 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 which specifically senses changes in the duration of time that shorter wavelength light (blue light) is present in order to sense time of year and seasonal shifts which helps regulate or infradian rhythms (multi-day cycles that dictate longer process like the menstrual cycle, hair growth, or seasonal depression).
Because of all these sensory perceptions, mostly of various wavelengths of light but also unconscious changes in our body like contractions of blood vessels or stretching in our digestive system, 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 disorder (ADD), 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 underestimate. This time blindness is what produces 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 also leads to disorientation. You put a pot of water on to boil and step away “for five minutes” only to find yourself scouring the grout lines in the bathroom three hours later, suddenly realizing that three hours have passed, there’s a pot on the stove, and you can’t figure out when or why you started scouring grout lines in the first place.