The human brain is the most complex biological system in the world. It contains about 86 billion neurons (brain cells) and has a variety of brain regions, each of which controls a different, specialized function.
Your brain’s different regions work together to keep your body running and give you the experience of consciousness. It’s one of the most critical organs in your body.
Your brain can be divided into four major brain regions: your cerebral cortex, limbic system, brainstem, and cerebellum. Here’s a look at each area and what it does for you.
Cerebral Cortex: Consciousness, Planning, Sensory Perception
When you look at a picture of a brain, you see the cerebral cortex. It’s the outermost layer of your brain—it’s just below your skull and wraps around the deeper, inner brain regions like a helmet.
The cerebral cortex is by far the largest brain region. It’s also what makes humans unique. The cortex controls your:https://www.jneurosci.org/content/37/40/9603https://www.ncbi.nlm.nih.gov/books/NBK537247/
- Sense of self
- Rational thought
- Sensory perception (sight, smell, hearing, touch, taste)
- Physical movement
You can divide the cerebral cortex into four regions, known as lobes: your frontal, parietal, temporal, and occipital lobes.
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Your frontal lobe is just below your forehead. It’s the most evolved part of your brain and is responsible for the higher-level cognition unique to humans.
The frontal lobe controls your reasoning, language, planning, imagination, social intelligence, and impulse control, as well as voluntary physical movement.
Damage to your frontal lobe can cause a variety of disordered behavior, including increased impulsivity, addiction, increased risk-taking, poor adherence to social norms, and changes in sexual behavior.
A classic example is Phineas Gage, a railroad foreman who lived in the mid-1800s. In 1849, Gage was at work on the railroad, tamping down explosives with an iron bar.
He accidentally detonated them, propelling the iron bar through the left side of his jaw and out through the top of his head. Gage survived the incident, but the bar destroyed most of his left frontal lobe.https://books.google.com/books?id=pgMHAAAAcAAJ&pg=PA12-IA2#v=onepage&q&f=false
After the accident, friends and family reported that Gage was a different man.https://en.wikisource.org/wiki/Recovery_from_the_passage_of_an_iron_bar_through_the_head He lost a great deal of impulse control and began gambling, flirting with other women in front of his wife, swearing constantly, and saying outrageous things at social gatherings. He also developed a temper and was quick to anger.
Gage’s case shows the importance of your frontal lobe: it allows you to think, plan, and keep your impulses and emotions under control.
All that said, a few years after the accident, Gage had largely returned to his former personality—a testament to how well your brain can adapt, even in the face of massive damage.
Your temporal lobes are located beneath your ears on each side of your head. You have a left and right temporal lobe; together, they control your hearing, language processing, speech skills, and memory.
Damage to the temporal lobes can cause hearing loss, speech problems, inability to understand language, and impaired memory.
A classic example of temporal lobe damage is Wernicke’s aphasia. A small area of the brain called Wernicke’s area, located in the rear upper third of your temporal lobes, controls your ability to understand language.
People with Wernicke’s aphasia speak in fluent gibberish. They talk effortlessly and with normal speech patterns—the right pauses, inflections, syntax, and so on—but the words they choose make no logical sense. They can produce language, but thanks to temporal lobe damage, they don’t understand it.
Your parietal lobe is right under the top of your head, in the middle of your brain. It controls pain and the sensation of touch, as well as fine sensation (your ability to judge texture, weight, size, and shape), taste, and temperature.
Damage to the parietal lobe can cause you to lose your ability to judge the size and temperature of objects.
It can also lead to other, oddly specific deficits. Gerstmann’s Syndrome, for example, comes from parietal lobe damage. People who have it are unable to recognize or identify fingers—both their own fingers and those of other people. They also have trouble writing, struggle to do basic math, and can’t distinguish left from right.https://www.ninds.nih.gov/Disorders/All-Disorders/Gerstmanns-Syndrome-Information-Page
Your occipital lobe is in the back of your head. Its main job is to control your vision and visual processing.
Your occipital lobe receives input from your optic nerve, a two-pronged nerve pathway that sends visual information from your eyeballs to your brain. Interestingly, your optic nerve crosses over in the middle of your brain—meaning, for example, turning off your left occipital lobe would cause vision loss in your right eye.
Damage to the occipital lobe causes all kinds of unusual disorders. An example is prosopagnosia, also called face blindness. There’s a specific region in your occipital lobe dedicated to recognizing faces and reading facial expressions—two very important tasks for social creatures like humans.
People with damage to that region can’t distinguish one face from another. They may not even recognize long-time friends and family members. However, most people with face blindness develop other skills to compensate, like remembering people’s voices, mannerisms, or defining physical characteristics.
Together, these four lobes—frontal, temporal, parietal, and occipital—make up your cerebral cortex. They’re responsible for many of the abilities and behaviors unique to human beings.
Limbic System: Emotion, Memory, Hunger, Fear
Your limbic system is in the very center of your brain, buried a level below your cerebral cortex.
While your limbic system is much smaller than your cortex, it’s a functionally diverse and very important part of your brain. It includes your:
- Hypothalamus. A brain region that controls your hunger, thirst, body temperature, and sleep rhythm.https://www.ncbi.nlm.nih.gov/books/NBK535380/
- Thalamus. A relay station that sends sensory information to the rest of your body. For example, if you’re walking and you see a pole in front of you, your thalamus sends that information to other parts of your brain, telling you to move and avoid the pole.
- Amygdala. The emotional center of your brain. Your amygdala generates emotions in response to stimuli in your environment. If you see a puppy and feel happy, that’s your amygdala at work. It also processes fear and controls your fight-or-flight response—identifying threats in the external world and prompting you to deal with or avoid them.
- Hippocampus. The memory center of your brain. Your hippocampus controls learning, as well as both short-term and long-term memory. It also works with your amygdala to control your fight-or-flight response.
These four regions make up your limbic system and control your learning, memory, emotion, hunger, and fear.
Damage to your limbic system causes memory loss and trouble regulating your emotions. Alzheimer’s Disease is a good example—it gradually destroys the hippocampus, leading to memory loss that gets worse as the damage progresses.
Brainstem: Breathing, Heartbeat, Reward
Your brainstem is located at the very base of your brain, just above your spine.
The brainstem is the oldest part of your brain; it was the first to evolve, and it controls your basic bodily functions, like heart rate, blood pressure, breathing, and sleep-wake cycles.https://www.ncbi.nlm.nih.gov/books/NBK544297/ It also indirectly influences your hearing and vision.https://pubmed.ncbi.nlm.nih.gov/31283463/
The brainstem is also home to your brain’s reward pathway (technically called the mesolimbic dopamine pathway). Pleasurable things, like food, sex, and rewarding drugs, flood your reward pathway with dopamine, giving you the sensation of pleasure and driving you to repeat those activities.
Damage to the brainstem is often fatal because it compromises the basic functions that keep your body alive.
Cerebellum: Balance, Motor Skills, Reflexes
Your cerebellum sits behind your brainstem at the very back of the base of your brain, right above your neck.
Cerebellum is Latin for “little brain,” which is appropriate. It looks like a miniature version of the rest of the brain and visually appears to be somewhat separate from it (although it isn’t; the cerebellum works in unison with your whole brain).
The cerebellum’s biggest roles are balance, coordination, and motor control. It’s important for maintaining your posture and allowing you to move in a precise, controlled way. It also controls your reflexes.
Alcohol affects your cerebellum, which is why you lose balance and fine motor skills when you’re drunk, and why your reflexes slow down.
Cerebellar damage makes it difficult to stay balanced and move in a coordinated way. It can also make it difficult to judge distance; people with impaired cerebellums often run into things because they don’t have an accurate understanding of their body’s position in space.
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Your brain is the control center of your entire body. It’s responsible for just about everything, from your sensory experiences to your heartbeat. It gives rise to your personality, your conscious thoughts, and everything else that makes you who you are.
The brain’s four major regions—the cerebral cortex, limbic system, brainstem, and cerebellum—all work together to create the consciousness you live every day.