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First, let's take this totally scientific poll.
Many of you probably answered in the 30-40% range, and perhaps some of you were up in the 50% or the 70% range.
According to Harvard professor Jeff Lichtman, who starts his courses by asking his students the same question, the answer is actually around "three inches," or 0.0047348 %.
The amount of information scientists simply don't know about the brain is part of the reason why there are so many hurdles in the way of developing effective commercial BMI.
So what DO we know about this thing?
So what DO we know about this thing?
To get an initial grasp of the brain itself, we need to put it into some context.
Most people think you have your hair, then your skin, then your skull, but there are actually multiple layers between the skin and the skull.
Under the skull, there are three main layers that act as shock absorbers and stabilize the brain so it doesn't just float around aimlessly in your head.
Under the skull, there are three main layers:
On the outside, there's the dura mater (which means "hard mother" in Latin). This layer is flush with the skull and fairly sensitive; pressure or contusions on the dura mater often cause bad headaches.
Underneath, there's the arachnoid mater ("spider mother") which is a layer of skin and a gap with a bunch of stretchy fibers. These fibers stabilize the brain in place and act as shock absorbers when trauma occurs. This area is filled with spinal fluid, which keeps the brain buoyant since the density of the fluid is similar to that of water.
Closest to the brain you have the pia mater ("soft mother"). This is a delicate layer of skin that is fused with the outside of the brain.
The brain and its three sections
The brain and its three sections
After digging through the skull, we're left with what is essentially the most complex object in the known universe (or what neuroengineer Tim Hanson calls “one of the most information-dense, structured, and self-structuring matter known.”) At first glance, the human brain may seem to be fairly confusing because it's difficult to know where to start and what sections of the organ correspond to the behaviors people are familiar with.
Neurologist Paul McLean came up with a simplified version that depicts the reptile brain evolving first, then mammals, and then a third brain that allows humans to achieve a level of brain cognition that outstrips virtually every other animal.
The Reptilian Brain (Brain Stem + Cerebellum)
The Reptilian Brain (Brain Stem + Cerebellum)
The reptilian brain deals with the most basic functions and keeps your body up and running. It's also the most ancient part of the brain.
The medulla oblongata
The medulla oblongata just really wants you to not die. It controls a lot of involuntary things like heart rate, breathing, and blood pressure. It also makes you vomit when you think you've been poisoned.
The pons
The pons does a little bit of everything. It controls swallowing, bladder control, facial expressions, chewing, saliva, tears, and posture.
The midbrain
The midbrain deals with an even wider variety of functions than the pons. It controls vision, hearing, motor control, alertness, and temperature control.
The cerebellum
Latin for "little brain." It helps you stay balanced and coordinated.
The Paleo-Mammalian Brain (The Limbic System)
The Paleo-Mammalian Brain (The Limbic System)
This part of the brain deals with basic survival urges. Basically, if you're doing something your dog might do - eating, drinking, reproducing, fighting, or hiding from a threat, your limbic system is probably behind it.
The limbic system is also in charge of emotions, which, for a complex social species, is an integral part of surviving.
The amygdala
The amygdala is basically an emotional mess. It controls anxiety, sadness, and responses to fear. There are actually two amygdalae, and the left one has been shown to be more balanced, producing happy emotions on top of the bad ones. The right one is pretty much always in a bad mood.
The hippocampus
Greek for "seahorse," because it looks like one. It acts as a sort of scratchboard for short-term memory. Over time, older memories are "wiped off" to make room for newer memories. Amnesia is nearly always caused by damage to the hippocampus. Alzheimer's also starts in the hippocampus before working its way through different parts of the brain, which is why one of the early signs of this disease is problems with simple short-term memories.
The thalamus
Since it sits right in the middle of the brain, it uses its position to act a sort of sensory middleman, receiving information from your sensory organs and sending it to your cortex for processing. When you go to sleep, the thalamus goes to sleep with you. The exception is your sense of smell, which is the one sense that bypasses the thalamus. It's why smelling salts are sometimes used to wake up unconscious people. Fun fact: the olfactory bulb is thought to be the oldest of all the senses. Unlike the other senses, smell is located deep within the limbic system, where it works in close proximity to the hippocampus and amygdala, which is why smell is so closely linked with memory and emotion.
The Neo-Mammalian Brain (The Cerebrum)
The Neo-Mammalian Brain (The Cerebrum)
The cerebrum (Or neocortex. Or cerebral cortex. Or pallium. Whatever.) is what makes you you. It covers the outside of the brain and handles basically everything - sensory processing, thinking, planning, language, movement, and personality.
It'd be unfair to say that each lobe does only one set of specific things because they each do so much and there's a lot of overlap, but here's a simplification:
The frontal lobe
Here it is. It handles personality, along with what most people think of as "thinking" - reasoning, planning, and executive function. The frontal lobe is also in charge of your body's movement.
The parietal lobe
Among other things, the parietal lobe controls your sense of touch.
The temporal lobe
Where a lot of your memory lives. And because it's right next your ears, it also houses the auditory cortex.
The occipital lobe
The occipital lobe is pretty straightforward. It's in the back of the brain and mostly just controls vision, which is why it contains the visual cortex.
It's a common misconception that these lobes are major chunks of the brain, but actually, the cortex is only the outer 2 mm of the brain. The space underneath is just wiring.
If you took the cortex off of the brain and spread it out, you'd get a 2mm-thick sheet about the size of a dinner napkin. All of the thinking, feeling, memory-making, creating, panicking, etc. that occurs over the course of your life takes place in that napkin.
“Anatomy of the Brain.” AANS, American Association of Neurological Surgeons, www.aans.org/Patients/Neurosurgical-Conditions-and-Treatments/Anatomy-of-the-Brain.
Sanders, Shannon. Beautiful 3-D Brain Scans Show Every Synapse | National Geographic. YouTube, National Geographic, 30 Jan. 2014, www.youtube.com/watch?v=nvXuq9jRWKE.
Urban, Tim. “Neuralink and the Brain's Magical Future.” Wait But Why, 20 Apr. 2017, waitbutwhy.com/2017/04/neuralink.html.
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