The cerebrum

The cerebrum, also known as the neocortex (executive brain), came out of the limbic system--it is the part of the brain that developed most recently in evolutionary terms. The cortex enables us to comprehend sensory information and plan accordingly. The neocortex is responsible for higher order thinking and symbolic communication, art and ideas, and long-term planning. The billions of connections between the limbic system and the cerebrum allow for the free-flow of information between these layers. The cerebrum is proportionately larger in animals that are able to take in sensory information and analyze it in some way. But only in humans is it so massive and complex. It is made up of right and left cerebral hemispheres, with a large groove called the cerebral fissure separating the two sides. Deep inside the brain, in the middle, is the corpus callosum, a bundle of nerve fibers connecting the halves of the brain, allowing information to move back and forth between the two sides. It is estimated that if the cortex were unfolded, its area would be three times larger than the surface of the brain. This folding accomplishes an important conservation of space, which means many more nerve cells are concentrated in each unit of volume. The following figure shows the cerebrum:

The cerebrum consists of the following parts:

• Frontal lobes: Planning, strategic thinking, inhibition, motor control--the frontal lobes are involved with intellect and the ability to fit into a social group, helping us plan and prioritize, concentrate and recall, and exert control over our behavior. Damage to the most forward section of the frontal lobes can cause offensive social behaviors. Toward the back of the frontal lobe is the motor area, a strip of brain with distinct sections controlling motor activity such as swallowing, chewing, talking, and movement of the hands, legs, toes, and so on. Doctors often need to map this area of the brain by using cortical stimulation before surgery to make sure they know exactly where the functions are otherwise, they might disturb or remove tissue that would affect those functions.

• Parietal lobes: Logic, math, taste, pain, sensations of pressure, pain, and temperature. The parietal lobes have a sensory area concerned with sensations coming in from the eyes, ears, nose, tongue, and other organs, and a motor area that controls movement.

• Occipital lobes: Visual processing--the occipital lobes are the visual center of the brain. Making sense of information coming into the brain from the eyes. The left occipital lobe receives input from the right field of vision, and the right occipital lobe receives input from the left field of vision.

• Temporal lobes: Memory, auditory processing, sensory integration--the temporal lobes are involved with speech and language, hearing, and memory. The temporal lobes have additional complex features.

The rational brain (neocortex) assists us with functions related to thinking and language: planning, questioning, making decisions, solving problems, and generating new ideas. This layer is connected to the emotional brain with millions of connections, allowing the emotional and the thinking brains to influence one another in a myriad of ways and providing rich data on which to draw conclusions and initiate action. But, significantly, the prefrontal cortex can be hijacked by the limbic system in the event of a perceived threat (whether imagined or real). Our prefrontal brain can go offline as blood flow is directed to the deeper limbic system--the first responder on a priority mission--to keep us safe.