THE HUMAN BRAIN AND LOCALIZATION OF THE LANGUAGE IN IT.

The brain is the most complex organ of the body. The surface of the brain is the cortex, often called "gray matter", consisting of billions of neurons (nerve cells) and glial cells (which support and protect the neurons. The cortex is the decision-making organ of the body. It is the organ that most distinguishes human from other animals. Somewhere in this gray matter resides the grammar that represents our knowledge of language.
The brain is composed of a right and a left cerebral hemisphere, joined by the corpus callosum. In general, the left hemisphere controls the right side of the body and the right hemisphere controls the left side. If you point with your right hand, the left hemisphere is responsible for your action.


The Localization of Language In The Brain
In the early nineteenth century, Frans Joseph Gall proposed the theory of Localization, which is the idea that different human cognitive abilities and behaviors are localized in specific parts of the brain, he proposed that language is located in the frontal lobes of the brain because as a young man he had noticed that the most articulate and intelligent of his fellows students had protruding eyes, which he believed reflected overdeveloped brain material.

Aphasia: The study of aphasia has been an important area of research in understanding the relationship between the brain and language. Aphasia is the neurological term for any language disorder that results from acquired brain damage caused by disease or trauma. In the second half  of the nineteenth century, significant scientific advances were made in localizing language in the brain based on the study of people with aphasia. In the 1860s the French surgeon  Paul Broca proposed that language is localized in the left hemisphere of the brain, and more specifically in the front part of the left hemisphere (Broca's area).
Patients with injuries to Broca's area may have Broca's aphasia as it is often called today also called (agrammatic aphasics). Broca's aphasia is characterized by labored speech and certain kind of word-finding difficulties, but it is primarily a disorder that affects a person's ability to form sentences with the rules of syntax.

Split brains: An extreme measure used to help people suffering from intractable epilepsy is a procedure of "splitting the brain"  in which a surgeon severs the corpus collosum, the fibrous network that connects the two halves. When this pathway is severed there is no communication between the two brains, making it possible to test the function of each hemisphere without interference from the other. In people who has gone split-brain surgery, the two hemisphere appear to be independent, and messages sent to the brain result in different responses, depending on which side receives the message. For example, if a pencil is placed in the left hand of a split-brain person whose eyes are closed, the person can use the pencil appropriately but cannot name it because only the left hemisphere can speak.

Neural evidence of phenomena 
There are a lot of new advanced techniques that reveal how the healthy brain reacts to particular linguistic simuli. For example, researches observe how the normal brain responds in deciding whether two or more sounds are the same or different, whether a sequence of sounds constitutes a real or possible word, or whether a sequence of words forms a grammatical or ungrammatical tense.