For other articles about other subjects named brain see brain (disambiguation).

For information about the human brain in specific, please see its article.

In the anatomy of animals, the brain, or encephalon, is the supervisory center of the nervous system. Although the brain is usually cited as the supervisory center of vertebrate nervous systems, the same term can also be used for the invertebrate central nervous system. In most animals, the brain is located in the head.

Mouse's Brain	Cat's Brain

The brain controls and coordinates most movement, behavior and homeostatic body functions such as heartbeat, blood pressure, fluid balance and body temperature. Functions of the brain are responsible for cognition, emotion, memory, motor learning and other sorts of learning.

The brain is primarily made up of two types of cells: glia and neurons. Glia function primarily to support and protect the neurons. The neurons carry information in the form of electrical pulses known as action potentials. They communicate with other neurons in the brain and throughout the body by sending various chemicals called neurotransmitters across gaps known as synapses. Small invertebrates such as insects may have a million neurons in the brain, larger vertebrate brains have over one hundred billion neurons. The human brain is particularly complex and enlarged.

A smart device

Brains in nature

Although many classes of animals have nervous systems, three groups of animals, with some exceptions, have notably complex brains: the arthropods (for example, insects and crustaceans), the cephalopods (octopuses, squid, and similar mollusks), and craniates (vertebrates and their cousins). The brains of arthropods and cephalopods arise from twin parallel nerve cords that extend through the body of the animal. The arthropod brain consists of a large opitical lobes behind each eye for visual processing and a central brain with three divisions. The cephalopod brain has a central group of lobes known as circumesophageal lobes that are flanked by two large optical lobes on the left and right (Butler, 2000).

The brains of craniates develop from the anterior section of a single dorsal nerve cord, which later becomes the spinal cord. In craniates, the brain is protected by the bones of the skull. Vertebrates are characterized by increasing complexity in the cerebral cortex as one moves up the phylogenetic and evolutionary tree. Primitive vertebrates, like fish, reptiles, and amphibians have cortices with less than six layers of neurons, a structure known as allocortex (Martin, 1996). More complex vertebrates like mammals have developed six-layered neocortex in addition to having some parts of the brain that are allocortex (Martin, 1996). In mammals, increasing convolutions of the brain, called gyri, are characteristic of animals with more advanced brains. These convolutions evolved to provide more surface area for a greater number of neurons while keeping the volume of the brain compact enough to fit inside the skull.

Brains in medicine

The brain, along with the heart, is one of the two most important organs in the human body. Loss of function in this organ fufills some definitions of death. Injuries to the brain tend to affect large areas of the brain, sometimes causing major deficits in intelligence, memory and control of the body. Head trauma, caused by automobile accidents or other blows to the skull, is a leading cause of death. Often in these cases, more damage is caused by swelling, or edema, than by the impact itself. Stroke, caused by blockage of blood vessels in the brain, is another major cause of death and brain damage.

Other problems in the brain can be more accurately classified as diseases than injuries. Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and Huntington's disease, are caused by the gradual death of individual neurons leading to decrements in movement control, memory, and thinking abilities. Currently, only the symptoms of these diseases can be treated, but stem cell research may offer a cure. Mental illnesses, such as clinical depression, schizophrenia, bipolar disorder, and post-traumatic stress disorder, are now recognized as having a biological basis in the brain. These disease can be treated by psychiatric therapy, by drugs, or by a combination of treatments.

Some diseases that affect the brain are caused by germs. Viral or bacterial infection of the meninges, the membrane that covers the brain, can lead to meningitis. Bovine spongiform encephalopathy is a deadly disease among cattle and is linked to prions.

Some brain disorders are congenital. Tay-Sachs disease, Fragile X syndrome, Down syndrome, and Tourette syndrome are all linked to genetic or chromosomal errors. Malfunctions in the embryonic development of the brain can be caused by genetic factors or by drug use or disease in the mother.

Brains in philosophy

Some philosophers consider that "brain" is synonymous with "mind", while others believe that the mind is the software of the hardware-brain. This issue, called the mind-body problem, and many others are the subject of the philosophy of mind: what is consciousness? Do non-human animals have consciousness?

Another branch of philosophy, epistemology, discusses the notion that we could be brains in vats, and that the reality around us could be simulated. While not taken as a fact by philosophers, it is used as an argument towards philosophical skepticism.

Artificial brains

Computer scientists have produced computer systems called neural networks that are loosely based on the structure of neuron connections in the brain. Artificial intelligence seeks to replicate brain function (although not necessarily brain mechanisms) more exactly, but this has not yet proven successful. Creating an algorithm to mimic a biological brain is extremely difficult because the brain is not a static arrangement of circuits, but a network of vastly interconnected neurons that are constantly changing their connectivity and sensitivity. More recent work in both neuroscience and artificial intelligence models the brain using the mathematical tools of chaos theory and dynamical systems.

Interfacing brains with machines

The activity of a brain can be detected by electrodes, raising the possibility of "brain-computer interface".

The reverse path has also been demonstrated; brain implants have been used to generate artificial hearing and (crude and experimental) artificial vision for deaf and blind people, and brain pacemakers are now common to regulate brain activity in conditions such as Parkinson's disease.

Both of these avenues of research have potentially serious ethical implications.

For example, using electrodes in a brain and a remote control, researchers have been able to remotely control the movements of a rat. This offers the possibility to create an electronically-controlled biological "ratbot" that could go in dangerous places.

The study of brains

Fields of study

The brain is studied by several areas of science. Neuroscience seeks to understand the nervous system, including the brain, from a biological perspective. Psychology seeks to understand behavior and the brain. The terms neurology and psychiatry usually refer to medical applications of neuroscience and psychology, respectively. Cognitive science seeks to unify neuroscience and psychology with other fields studying the brain, such as computer science (as in Artificial intelligence, etc) and philosophy.

Methods of observation

Each method for observing activity in the brain has its advantages and drawbacks. Electrophysiology, in which wire electrodes are implanted in the brain, allows scientists to record the electrical activity of individual neurons or fields of neurons, but since it requires invasive surgery, this is a technique usually reserved for lab animals. By placing electrodes on the scalp, electroencephalography (EEG) measures brainwaves, which are the mass changes in electrical current from the cerebral cortex, but can only detect changes over large areas of the brain and very little sub-cortical activity. Functional magnetic resonance imaging (fMRI) measures changes in blood flow in the brain, but the activity of neurons is not directly measured, nor can it be distinguished whether this activity is inhibitory or excitatory. Behavioral tests can measure symptoms of disease and mental performance, but only provide indirect measurements of brain function and may not be practical in all animals. Post-mortem analyses of brains allow for the study of anatomy and protein expression patterns but can only be done after the human or animal is dead.

Myths

The following are some common myths or misconceptions about the mind and brain, perpetuated through common or urban myths, the media, and the promotion of dubious products to consumers (Sala, 1999). A number of practitioners of pseudoscience, new age philosophies, and mystical or occult practices are known to use some of these myths as a part of their belief systems. Also see popular psychology.

• Myth: The human brain is firm and grey. The fresh/living brain is actually very soft, jelly-like and deep red. They do not become firm and grey until they have been preserved with various chemicals/resins.
• Myth: Humans use only 10% or 1% of their brain. Though the brain still holds mysteries that are being studied, every part of the brain is known to have a function.
• Myth: Mental abilities are separated into the left and right cerebral hemispheres.
• Myth: Creativity can be easily developed using the simple brainstorming/lateral thinking techniques.
• Myth: Increased age leads to reduced mental ability. Mental ability is affected by how much we use our brains, both for tasks involving coordination of body movement and in pure thought processes, such as problem solving.
• Myth: Learning can be achieved more powerfully through subliminal techniques.
• Myth: Hypnosis can lead to perfect recall of details. Not only is this not entirely true, an incompetent or deceptive hypnotist can actually implant memories of events that never occurred.

Inside brains

Anatomy

Rabbit brain
1:olfactory bulb 2:cerebral cortex 3:cerebellum 4:medulla oblongata