Human brain

The human brain controls the central nervous system (CNS), by way of the cranial nerves and spinal cord, the peripheral nervous system (PNS) and regulates virtually all human activity. Involuntary, or "lower," actions, such as heart rate, respiration, and digestion, are unconsciously governed by the brain, specifically through the autonomic nervous system. Complex, or "higher," mental activity, such as thought, reason, and abstraction, is consciously controlled.
Anatomically, the brain can be divided into three parts: the forebrain, midbrain, and hindbrain; the forebrain includes the several lobes of the cerebral cortex that control higher functions, while the mid- and hindbrain are more involved with unconscious, autonomic functions. During encephalization, human brain mass increased beyond that of other species relative to body mass. This process was especially pronounced in the neocortex, a section of the brain involved with language and consciousness. The neocortex accounts for about 76% of the mass of the human brain; with a neocortex much larger than other animals, humans enjoy unique mental capacities despite having a neuroarchitecture similar to that of more primitive species. Basic systems that alert humans to stimuli, sense events in the environment, and maintain homeostasis are similar to those of basic vertebrates. Human consciousness is founded upon the extended capacity of the modern neocortex, as well as the greatly developed structures of the brain stem.

Common misconceptions
Visualization of a diffusion tensor imaging (DTI) measurement of a human brain. Depicted are reconstructed axon tracts that run through the mid-sagittal plane. Especially prominent are the U-shaped fibers that connect the two hemispheres through the corpus callosum (the fibers come out of the image plane and consequently bend towards the top) and the fiber tracts that descend toward the spine (blue, within the image plane).
The following are some commonly held misconceptions of the mind and brain perpetuated through urban legends, mass media, and the promotion of dubious products to consumers (Sala, 1999):
Holes in the brain: Often lesions in the brain, from injury, disease, or drug use, are described as 'holes', however, these 'holes' are in fact not cavities, most often are simply inactive areas of the brain where neurons no longer fire.
The human brain is firm and grey: The fresh/living brain is actually very soft, jelly-like, and deep red. It does not become firm and grey until it has been preserved with various chemicals/resins.
Humans use only 10% or less of their brain: Even though many mysteries of brain function persist, every part of the brain has a known function
This misconception most likely arose from a misunderstanding (or misrepresentation in an advertisement) of neurological research in the late 1800s or early 1900s when researchers either discovered that only about 10% of the neurons in the brain are firing at any given time or announced that they had only mapped the functions of 10% of the brain up to that time (accounts differ on this point).
Another possible origin of the misconception is that only 10% of the cells in the brain are neurons; the rest are glial cells that, despite being involved in learning, do not function in the same way that neurons do.
Einstein is reported as quipping that people typically only use 10% of their brains. The popular press took this as fact, although the comment was meant only facetiously.
Lower level of brain activation does not mean a lower performance of cognitive functions; this variable has confounded scientists, because some 'gifted' individuals showed less activity than the average person. Haier proposed that indeed more gifted individuals might possess more efficient brain circuits.
Some New Age proponents propagate this belief by asserting that the "unused" ninety percent of the human brain is capable of exhibiting psychic powers and can be trained to perform psychokinesis and extra-sensory perception.
Mental abilities are absolutely separated into the left and right cerebral hemispheres: Some mental functions such as speech and language (cf. Broca's area, Wernicke's area) tend to be localized to specific areas in one hemisphere. If one hemisphere is damaged at a very early age however, these functions can often be recovered in part or even in full by the other hemisphere. Other abilities such as motor control, memory, and general reasoning are spread equally across the two hemispheres. See lateralization of brain function.
Learning can be achieved more powerfully through subliminal techniques: The extent to which subliminal techniques can influence learning depends largely on what level of perception the techniques affect.
New neurons cannot be created, they only die as one ages. In fact, new neurons can grow within the mature adult brain; this process is known as neurogenesis. Regardless of neuron growth or death, brain function and capabilities can be learned and developed throughout life.
The brain cells do not duplicate at all after it has developed (around late childhood). Although most of the brain does not grow, the cells in the hypothalamus are still growing.

Neurolinguistics
In human beings, it is the left hemisphere that usually contains the specialized language areas. While this holds true for 97% of right-handed people, about 19% of left-handed people have their language areas in the right hemisphere and as many as 68% of them have some language abilities in both the left and the right hemisphere. The two hemispheres are thought to contribute to the processing and understanding of language: the left hemisphere processes the linguistic meaning of prosody, while the right hemisphere processes the emotions conveyed by prosody. Studies of children have provided some fascinating information: If a child has damage to the left hemisphere, the child may develop language in the right hemisphere instead. The younger the child, the better the recovery. So, although the "natural" tendency is for language to develop on the left, our brains are capable of adapting to difficult circumstances, if the damage occurs early enough.