The brain, along with the heart, is one of the two most important organs in the human body. Loss of function in this organ fulfills 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 rather 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, also known as mad cow disease 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 (strong AI theorists) believe
that the mind is the software of the hardware-brain. This issue,
related to the mind-body problem, and many others are the subject
of the philosophy of mind: what is consciousness? Do non-human animals
have consciousness?
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.
