The cerebrum is the largest part of the brain, and it is divided from front to back into two sections. The left cerebrum is the left side of the brain and is also called the left hemisphere. The left and right cerebral hemispheres have slight differences in their functions. This is called functional asymmetry. The left cerebrum is primarily responsible for speech, math and logic, and it is related to the functions of the right side of the body.
The left cerebrum is anatomically different from the right cerebrum. The structural differences between both hemispheres are called anatomical asymmetries. Part of the temporal lobe is larger on the left side than the same area on the right side. This physical difference exists at birth. The Sylvian fissure, which is a cleft or groove in the cerebrum, also has a more gradual arch shape on the left side than on the right.
In 1861, French neurosurgeon Paul Broca studied the brains of deceased patients who had difficulty speaking during their lives and found large lesions in their brains' left frontal hemispheres. His research resulted in the belief that the left hemisphere is important for speech and language. He identified an area in the left cerebrum that operates as a speech center; it is now called Broca’s area. German neurologist Carl Wernicke discovered a part of the left cerebrum in the left temporal lobe that is important for language. If this area is damaged, a person could still speak, but the words would not make sense.
In the 1960s, neurosurgeons Roger Sperry and Michael Gazzaniga studied the brains of people with epilepsy, a brain disorder that causes a person to have seizures. These studies, called “split brain experiments,” demonstrated that the left cerebrum is important for speech, math and analytical tasks, and the right cerebrum is important for space perception, music and art. Roger Perry received the Nobel Prize in Physiology or Medicine in 1981 for his “split brain” studies.
The left and right cerebrums are connected by the corpus callosum, which is made up of nerve fibers that run crosswise between the two hemispheres, and the corpus callosum helps the two hemispheres communicate with each other. The left cerebrum controls muscles on the right side of the body. It is the dominant hemisphere for motor control of right-handed people. The right cerebrum is important for the motor control of left-handed people. If one side of the brain is damaged, it will affect the opposite side of the body.
