There are two primary sections of the brain that relate to language and communication, and if either section becomes damaged, the person will be unable to speak properly. The left frontal cortex of the brain is known as "Broca's Area," after a 19th century physician named Paul Broca. The second section is called "Wernicke's Area," after Broca's contemporary, Karl Wernicke. It is located further back and lower in the brain than Broca's Area, at the tail end of the temporal lobe. These two sections are connected by bundles of nerve fibers. When these connections are damaged, the person can understand language but their speech does not make sense and they cannot repeat words. In most people, both Broca's area and Wernicke's area are found only in the left side of the brain.
Scientists have studied how electrical stimulation of these areas of the brain can block language. They have also injected fast-acting anesthetics into the right or left carotid artery. The right artery supplies the right side of the brain, while the left artery supplies the left side. Injecting an anesthetic into either will put that side of the brain to sleep. They found that when the left hemisphere of the brain was asleep, patients were unable to speak when asked questions. But they would be able to answer questions if the right side of the brain was asleep.
But even though the left side of the brain is dominant when it comes to language, imaging studies of blood flow in the brain have shown that people with damage on the right side have trouble communicating the emotions involved with language. This disorder is called "aprosodia."
Test your child's abilities
Head turn test: Try this with your about six months old baby: move to your baby's side, so that you're just out of his or her view. Say baby's name and watch the reaction. See if he turns his head toward you. Then, when he turns his head back, say his name again.
Pointing test: For infants about nine months old. At this age, babies are learning non-verbal cues too. Point at an object nearby (but not one that is making noise.) Does the baby look at your finger or at the object to which you are pointing?