Your brain controls everything you do, feel, and think, from the obvious tasks like solving a math problem to the ones you never notice, like keeping your heart beating while you sleep. It weighs roughly three pounds, yet it consumes about 20 percent of your body’s total energy, even at rest. Every region handles different jobs, and they all work together around the clock to keep you alive, aware, and able to interact with the world.
How Brain Cells Talk to Each Other
Everything your brain does depends on one basic process: neurons sending messages to other neurons. You have roughly 86 billion of these nerve cells, and they communicate through a combination of electricity and chemistry. Inside a single neuron, messages travel as tiny electrical impulses. But when a message needs to jump from one neuron to the next, the process switches to chemical.
At the gap between two neurons, called a synapse, the sending cell releases chemical messengers called neurotransmitters. These float across the gap and lock onto matching receptors on the receiving cell, like a key fitting into a lock. Once the message is delivered, the neurotransmitter is either broken down or pulled back into the original cell to be reused later. This entire process happens in milliseconds, billions of times per second, across your entire brain.
Running Your Body Without Your Input
Most of what your brain does happens without you knowing. Your autonomic nervous system, managed largely by a small structure called the hypothalamus, handles processes you never consciously direct. It regulates how fast and hard your heart pumps, adjusts the width of your blood vessels to manage blood pressure, controls the airways in your lungs, and triggers sweating to cool your skin. The hypothalamus also produces hormones and manages hunger, thirst, body temperature, sexual arousal, and your sleep-wake cycle.
You don’t decide to digest your lunch or tell your pupils to shrink in bright light. Your brain handles all of it automatically, leaving your conscious mind free for other things.
Processing What You See, Hear, and Feel
Every second, your senses flood your brain with an enormous amount of raw data: light, sound, pressure, temperature, pain. Before any of that information reaches the parts of your brain that interpret it, nearly all of it passes through a relay station called the thalamus. Think of it as a post office that sorts incoming mail. The thalamus receives nerve signals from your eyes, ears, skin, and muscles, then routes each type of information to the correct processing area in the outer layer of your brain. The one exception is smell, which takes a more direct route to the frontal lobe.
The thalamus doesn’t just pass information along passively. It also helps prioritize what deserves your attention, filtering the vast stream of input so your brain focuses on what matters most at any given moment. That’s why you can tune out background noise in a coffee shop but snap to attention when someone says your name.
Thinking, Planning, and Self-Control
The front part of your brain, called the prefrontal cortex, is essentially your command center for higher-level thinking. It handles what scientists call executive functions: planning ahead, making decisions, solving problems, staying focused, and adjusting when circumstances change. It’s also where impulse control lives. When you resist the urge to check your phone during a conversation or stop yourself from saying something you’d regret, that’s your prefrontal cortex overriding a more automatic response.
Different sections within this region specialize in different tasks. Some areas handle working memory, holding information in your mind just long enough to use it (like remembering a phone number while you dial it). Others help you evaluate whether an experience is good or bad, regulate your emotions, or switch between tasks. The frontal lobe more broadly also plays a role in personality, movement, and speech production.
Emotions, Fear, and Memory
Deeper inside the brain, a group of structures called the limbic system handles your emotional life. The amygdala is central to how you experience emotions like fear, anger, and anxiety. It also helps you read social situations and form emotional memories, which is why a song can instantly bring back the feeling of a specific moment years later.
Nearby, the hippocampus is responsible for forming new memories. Without it, you could still recall old memories but couldn’t create new ones. The hypothalamus, which also runs your autonomic functions, ties into this emotional circuit by managing mood and producing hormones that affect how you feel throughout the day. These structures work together, which is why strong emotions tend to produce strong memories and why stress can disrupt both mood and the ability to think clearly.
Movement and Coordination
The cerebellum, a densely folded structure at the back and bottom of your brain, coordinates voluntary muscle movements and maintains your posture, balance, and equilibrium. It doesn’t initiate movement on its own. Instead, it fine-tunes the signals coming from other brain regions so your actions are smooth and accurate rather than jerky and imprecise. Every time you reach for a glass of water, walk across a room, or type on a keyboard, your cerebellum is calibrating the timing and force of dozens of muscles simultaneously.
The parietal lobe, located in the middle of the brain, contributes by helping you understand spatial relationships: where your body is in relation to the objects around you. It also processes touch and pain signals, giving you a physical sense of the world.
How Your Brain Learns and Adapts
Your brain is not a fixed machine. It physically rewires itself based on what you do, a property called neuroplasticity. Early in life, your brain creates far more connections between neurons than it will ever need. Over time, it follows a “use it or lose it” rule. Connections you use frequently get stronger. Connections you rarely use are marked for removal by specialized immune-like cells called microglia, which clear them away. This process, called synaptic pruning, makes the brain more efficient, organized, and faster at processing information.
This is why practice works. When you repeat a skill, whether it’s playing piano or speaking a second language, the neural pathways involved fire up again and again. Your brain strengthens those pathways, making the skill easier and more automatic over time. Pruning continues throughout life, though it’s most dramatic during childhood and adolescence.
What Happens While You Sleep
Sleep is not downtime for your brain. Even while you’re unconscious, your entire brain remains intensely active. One of its most important overnight tasks is waste removal. During the day, normal brain activity generates metabolic byproducts, including proteins that can cause problems if they accumulate. A cleaning system called the glymphatic system uses fluid to wash this waste out of your brain tissue.
This system works best during deep sleep (stage 3, also called slow-wave sleep). During this phase, the spaces between brain cells expand, allowing fluid to flow more freely and flush out waste more efficiently. Among the substances cleared are amyloid-beta and tau proteins, both associated with neurodegenerative diseases when they build up over time. A drop in the alertness chemical norepinephrine during deep sleep relaxes the system’s vessels, further improving the flow. This is one reason chronic poor sleep is linked to cognitive decline: your brain literally hasn’t had enough time to clean itself.
You Use All of It
The popular claim that humans only use 10 percent of their brain is completely false. Brain imaging and decades of research confirm that you use your entire brain every day. Different regions activate more or less depending on the task, but no part of the brain sits idle. As neuroscientist Eric Halgren at MIT’s McGovern Institute has noted, all of your brain is constantly in use and consumes a tremendous amount of energy, even during sleep. The brain will use 100 percent of what it has, though it can sometimes compensate when specific structures are damaged by rerouting functions to other areas.