The brain is a major part of the central nervous system. In vertebrates, the brain is connected to the spinal cord. In invertebrates' nervous systems, the brain can be a decentralized collection of neurons or a single ganglion. In the vertebrates, the brain is much more complex and is divided into three separate areas, the forebrain, the midbrain, and the hindbrain. The brain is involved in higher functioning such as decision-making, speech, and processing of the senses.
In adult humans, the brain weighs about 3 lbs., with 100 billion neurons, and up to 100 trillion connections.
Investigations using new techniques such as fMRI are expanding knowledge on the relationship between the brain and behavior.
Many atheist scientists believe that modern neuroscience is a subversion of free will, and that the brain is all there is to personality. This is to the direct exclusion of the soul (atman or that which takes rebirth) and the will of a higher being such as Buddhas, Bodhisattvas, gods, goddesses, God). For instance, if someone was to commit a crime, that person could be exonerated on the basis of his neurological abnormalities, which are not his fault. Descartes attempted to avoid this issue by placing the soul at the helm of the individual, stating that it was our spirits that truly drive us. The soul attached to the brain via the pineal gland, communicating with the corporeal matter by squeezing the central gland, and pumping cerebrospinal fluid through the body. However, his atheism left no place for communion of the soul with a higher being, and Descartes was also mistaken in the belief that only humans have pineal glands. Many religious scientists are now taking into account the soul, when they factor in free will, which allows for much more variation among individuals.