The expressive and comprehensive language areas of the brain are connected through a bundle of nerves. The language areas are believed to lie in the dominant hemisphere of an individual.
Language is the communication of thoughts, ideas and feelings, using arbitrary symbols or signals like vocal sounds, body language or written symbols. These symbols are bound by rules for combining its components, like rules of joining words into a sentence. Such a system is used by a set of people in a community or nation in common. Language processing is the manner in which human beings use words and string them together to communicate and also how this system is processed and understood by the listener. Most recent theories suggest that such processing is done by specific areas in the human brain.
Brain injuries, stroke, tumor and other damages to the brain that are focused in the speech and language areas can give rise to deficits in expressive or comprehensive language and thus hinder communication. About 25% to 40% of stroke survivors get aphasia or inability to speak, as reported by National Aphasia Association. Besides a direct effect on the language are of the brain, the aphasia could also be due to paralysis of the fascial muscles in aphasia patients. Other causes of damage to the speech and language areas of the brain are brain tumor, seizures, brain infection and dementia.