Brain

The brain is an organ that is the center of the nervous system in all vertebrate and most invertebrate animals. It is made of nervous tissue and is usually found in the head, near organs that help with vision, hearing, and olfaction. The brain is very important because it receives information from the body's senses, thinks about that information through thought, cognition, and intelligence, and helps control movement of muscle and the endocrine system.

In humans, the brain has billions of tiny cells called neurons. These neurons connect to each other through structures called synapses. These connections let the brain send quick signals through axons, helping the body react fast to changes in the environment. The brain also tells muscle cells to move and manages the release of hormones, which are chemicals that affect many body functions.

Brains give centralized control, helping animals respond quickly and work together. While simple actions can happen without the brain, more complicated actions need the brain to bring together many pieces of information. Scientists study the brain to learn how these cells work together, comparing brains across different animal species and focusing especially on vertebrates.

Structure

Cross section of the olfactory bulb of a rat, stained in two different ways at the same time: one stain shows neuronal cell bodies, the other shows receptors for the neurotransmitter GABA.

The brain comes in many shapes and sizes across different animals, but it always has some basic features in common. Scientists study the brain using many tools. They can look at it with their eyes, but they also use special methods to see tiny details.

All brains are made up of special cells called neurons and glial cells. Neurons are important — they send electrical signals through long arms to talk to other cells. These signals help the brain think, learn, and control the body. The brain also has many connections, which help it remember and change over time.

Evolution

The brain has evolved in animals to help them process information and control their movements. In very simple animals like sponges, there is no brain at all, but in animals with bodies that have left and right sides a small structure called a brain begins to form. This brain gets larger and more complex in animals with backbones (vertebrates) like fish, amphibians, reptiles, birds, and mammals.

Some animals without backbones, like insects and octopuses, also have complex brains. Scientists study these animals to learn more about how brains work. In vertebrates, the brain develops from three main parts early in an animal's growth. Over time, especially in mammals, the front part of the brain (forebrain) becomes much larger and more complex, helping with thinking and problem-solving.

Encephalization Quotient
Species	EQ
Human	7.4–7.8
Common chimpanzee	2.2–2.5
Rhesus monkey	2.1
Bottlenose dolphin	4.14
Elephant	1.13–2.36
Dog	1.2
Horse	0.9
Rat	0.4

Development

Main article: Neural development

Brain of a human embryo in the sixth week of development

The brain grows in a careful and planned way. It starts as a small bump at the front of a tiny cord and becomes more complex as it grows. Special cells called neurons are made in certain areas and then move to their right places. Once there, they connect to each other, forming pathways that help the brain work.

In animals with a backbone, the early steps of brain development are similar. The brain begins as a small plate that folds into a tube, then splits into different sections that will become the forebrain, midbrain, and hindbrain. These sections divide to form the parts of the brain we know today. The connections between neurons are not fully set from the start; they are refined over time, with some extra connections being removed to make the brain more efficient. In humans and many other animals, most brain cells are formed before birth, but a few areas continue to make new cells throughout life. Both genes and experiences shape the brain, with early experiences playing an important role in how the brain develops.

Physiology

Brain electrical activity recorded from a human patient during an epileptic seizure

The brain works with special cells called neurons. These neurons send and receive signals. The signals are made by chemicals called neurotransmitters. These chemicals connect at points called synapses. Each neuron usually uses the same neurotransmitter to talk to other neurons.

The brain also makes tiny electric fields when it is active. We can sometimes see these fields from outside the head using tools like EEG. The brain needs a lot of energy to work, and it gets this energy mostly from sugar in our blood. Special cells around neurons help keep everything running smoothly.

Function

Model of a neural circuit in the cerebellum, as proposed by James S. Albus

The brain collects information from our senses. It helps us understand what is around us and decide what to do. The brain uses what it senses along with our needs and past experiences to guide our movements.

The brain controls all our actions. It helps muscles work together in complex ways. It makes different parts of the body work together. The brain also manages our sleep patterns, keeps our body balanced, and helps us remember and learn new things.

Major areas involved in controlling movement
Area	Location	Function
Ventral horn	Spinal cord	Contains motor neurons that directly activate muscles
Oculomotor nuclei	Midbrain	Contains motor neurons that directly activate the eye muscles
Cerebellum	Hindbrain	Calibrates precision and timing of movements
Basal ganglia	Forebrain	Action selection on the basis of motivation
Motor cortex	Frontal lobe	Direct cortical activation of spinal motor circuits
Premotor cortex	Frontal lobe	Groups elementary movements into coordinated patterns
Supplementary motor area	Frontal lobe	Sequences movements into temporal patterns
Prefrontal cortex	Frontal lobe	Planning and other executive functions

Research

Main article: Neuroscience

"Brain research" redirects here. For the scientific journal, see Brain Research.

Neuroscience is the study of the brain and the nervous system. Psychology looks at how the mind and behavior work. Neurology is a medical field that treats diseases of the nervous system. The brain is also important in psychiatry, which helps people with mental disorders. Cognitive science mixes neuroscience with other areas like computer science and philosophy to better understand the brain.

Scientists study the brain in many ways. They look at its structure using special stains and microscopes. They also use tools like EEG to measure brain activity and fMRI to see which parts of the brain are working during different tasks. Computers help scientists understand how groups of brain cells might work together. Recent advances include studying genes and using advanced imaging to see how brain cells communicate and change over time.

Society and culture

As food

Animal brains are eaten in many different foods around the world.

In rituals

Some old clues from archaeological studies show that European Neanderthals may have eaten brains as part of their traditions.

The Fore people of Papua New Guinea have a tradition where they eat human brains during special ceremonies for people who have passed away. This was done to feel connected to the person who died. This practice led to a disease, but doctors later learned why.