By Dr Ananya Mandal, MD
The human brain is divided into two hemispheres. The left hemisphere is the "logical brain" and is involved in language and analysis and the right hemisphere is the "creative brain," involved in daydreaming and imagination. The left hemisphere controls the right side of the body while the right hemisphere controls the left side.
The earliest research on speech and language centers of the brain dates back to the early nineteenth century. Physicians noted that brain-injured patients with damage to the left hemisphere would lose power of speech and language abilities, while those with injuries to the right hemisphere did not lose this ability.
Recent studies have shown that in around 97% of people, language is represented in the left hemisphere. However, in about 19% of left-handed people, the areas responsible for language are in the right hemisphere and as many as 68% of them have some language abilities in both the left and the right hemispheres.
Determination of language areas
A procedure called cortical stimulation mapping is a technique that is used to analyze regions of the brain that are related to speech. On performing brain surgery to treat epilepsy or remove tumors for example, electrical stimulation of speech-related areas in the cortex prevents the patient from being able to name things that are shown to them and may also prevent their ability to produce grammatically coherent sentences. When such a site is indentified, it is spared, since damaging these areas could cause a temporary or permanent loss of speech.
Neural networks in the brain
Neural networks are established over time as an individual learns and experiences things. Language and speech skills are therefore acquired after birth. The human genome codes for the speech ability that will evolve as the brain is trained.
Speech and language brain regions
The visual cortex is the part of the cerebral cortex that is responsible for processing visual information.
The auditory cortex in the cerebral cortex processes auditory information and as part of the sensory system for hearing, performs both basic and higher hearing functions.
Wernicke's area is an area in the cerebral cortex related to speech and is involved in both spoken and written language. This area was named after Carl Wernicke, a German neurologist who discovered that the area is related to how words and syllables are pronounced.
Broca's area is an area in the frontal lobe of the brain that is related to the production of speech. The area is named after Pierre Paul Broca who noticed an impaired ability to produce speech in two patients who had sustained injury to the region.
Reviewed by Sally Robertson, BSc