What is the Cerebrum?

The cerebrum sits just on top of the brainstem. It has outer layers of grey matter with underlying sections of white matter. Grey matter is the darker tissue of the brain and consists mostly of nerve cell bodies. White matter consists of specialized tissue that increases the speed of electrical impulses that trigger many of the body’s functions. The outer layer of gray matter in the cerebrum is the cerebral cortex. Its surface has many ridges and furrows that experts call gyri and sulci.

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Researchers split the cerebral cortex into four sections: the frontal, parietal, occipital, and temporal lobes. The largest of these is the frontal lobe. It contains the primary motor cortex, which controls voluntary movement. It also contains the majority of the dopamine neurons in the brain, which are part of the reward, attention, planning, motivation, and short-term memory functions. The parietal lobe is responsible for touch sensory inputs, manipulating objects, and understanding numbers. At the back of the brain is the occipital lobe, the visual processing center. The temporal lobe is complex and plays a role in visual and auditory sensory inputs, language recognition, and memory creation.

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A deep groove the medical community calls the longitudinal fissure separates the left and right hemispheres of the brain. Each side of the brain tends to specialize in certain functions and activities, hence the term “left or right brained.” Typically, language and its related skills such as grammar and vocabulary lateralize to the left hemisphere in right-hand-dominant individuals, though this is bilateral or right-lateralized in around half of the left-hand-dominant people. Sensory processing, facial perception, and artistic ability usually present bilaterally. Number estimation and comparison are bilateral, though the actual calculations tend to use the left parietal regions.

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Humans have two hippocampi, one in each hemisphere of the brain. The hippocampus plays an important role in the transformation from short-term to long-term memory and in the spatial memory that allows humans to navigate. As with most sections of the brain, experts argue as to the exact functions the hippocampus provides. Typically, they agree that the hippocampus assists in the formation of new memories. Some experts also believe that it plays a role in remembering facts as opposed to just created memories. This section also seems to encode emotional context for the memories it helps create, allowing for a repeated emotional response to an event that has long since passed.

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A large neural structure in the cerebrum controls the sense of smell. This is the olfactory bulb and experts still debate its exact function. The four general functions experts believe it performs are odor discrimination, odor detection sensitivity, odor filtering, and allowing other parts of the brain to control the olfactory senses. The bulb receives information about an odor or smell from olfactory receptors in the nasal cavity. Then, it sends these signals to the amygdala, orbitofrontal cortex, and the hippocampus. This ties scents to memories and emotions.

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Within the brain are a group of neuron clusters. These basal ganglia connect to the cerebral cortex, thalamus, and brainstem and assist in controlling voluntary movements, habit learning, emotion, and cognition. For movement, the basal ganglia act as a filter system, inhibiting signals for movements that the brain doesn’t desire. Dopamine heavily influences the basal ganglia, which indicates the neuron clusters play a role in motivation. Finally, the basal ganglia may also affect decision making. The cerebral cortex queues several actions and the basal ganglia use context messages from other areas in the brain to decide on the best course of action.

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The primary motor cortex works alongside the premotor cortex, the supplementary motor area, and the posterior parietal cortex to plan movements. Within the primary motor cortex are Betz calls -- large neurons that, along with other cortical neurons, send signals from the brain to the muscles to trigger movements. However, the brain can’t send signals directly to the muscles without spasms or excess movement. Instead, the signals travel to the basal ganglia first; they inhibit certain signals while allowing others to travel along various pathways to the muscles, facilitating controlled voluntary movement.

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The brain encodes, stores, and recalls all types of information and experiences. These are memories, and they allow humans to develop language, relationships, and personal identities. Unlike a computer’s hard drive, the brain does not store memories in a single storage structure. Instead, it stores them in different regions of the brain. For example, the hippocampus plays a role in encoding long-term memories, but the brain does not store them there. Instead, experts believe the brain stores these memories in the temporal lobe.

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We recognize five distinct senses: taste, smell, sight, hearing, and touch. However, this is a general overview and neurologists have argued over the exact number of senses for years. Beyond the standard five senses, experts also recognize nociception, equilibrioception, proprioception, and thermoception. In order, these are the body’s ability to sense pain, balance, self, and temperature. Billions of receptors throughout the body send signals to the brain with information about what they experience. The sensory areas of the cerebrum receive and process these signals before passing them on to wherever they are needed.

Broca's area resides within the frontal lobe of the cerebrum. This region of the brain plays a role in language comprehension and production. It works alongside the section where the temporal and parietal lobes meet: Wernicke’s area. Together, these two regions of the cerebral cortex allow the brain to perform not only word creation and comprehension, but word association as well. A long tract of white matter connects these areas, and damage to either area or the tract can seriously impact speech capabilities.

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