Cerebral Cortex: Structure, Function & Diseases

The cerebral cortex refers to the outermost layer of the human cerebrum. The term derives from the Latin cortex (bark) cerebri (brain) and is often abbreviated as cortex.

What is the cerebral cortex?

The human cerebrum comprises about 85 percent of the total brain mass and is the youngest part of the brain in evolutionary terms. The overlying cerebral cortex performs a variety of human sensory perception tasks and, because of its large area, occupies about half of the total brain volume. The cortex is also called gray matter because of its high number of nerve cells, which bathe it in a reddish-brown to gray color. The number of neurons in the cerebral cortex ranges from 19 to 23 billion, depending on the size and sex of the individual. The neurons of the cerebral cortex process coded signals from the body’s individual sensory organs and convert them into specific impressions. The cerebral cortex is thus an essential component for our sensory perception. Some scientists also believe that they can locate the seat of consciousness in the anterior cerebral cortex. However, this research hypothesis, like the mystery of consciousness itself, is highly controversial.

Anatomy and structure

The cerebrum, divided into two mirror-image halves called hemispheres, extends from the frontal area through the sides to the back of the head and is located above the thalamus, hypothalamus, brainstem, and cerebellum. The cerebral cortex encasing the cerebrum is a layer two to five millimeters thick lying in numerous folds and convolutions. This folding allows for maximum surface area expansion in the limited space of the skull. In humans, the area of the cortex averages 1800 square centimeters. The characteristic structure of the cerebral cortex has evolved slowly over time in the evolution of mammals. The oldest parts include the paleocortex, which is responsible for the perception of smells and which translates as old cortex. The so-called archicortex, which is often counted as part of the limbic system and influences emotional reactions, and the hippocampus, which is crucial for memory, also developed early in history. These ancient portions of the cerebral cortex, however, make up only one-tenth of the total cortex. The remaining 90 percent is called the neocortex, or new cortex. The neocortex became more and more complex in structure and composition analogous to the higher development of the sensory organs, as happened for example with skin and mucous membranes, musculature, taste organs and inner ear. The entire cerebral cortex can also be roughly divided into four to six lobes, called lobi, whose boundaries form the most prominent furrows.

Functions and tasks

Different lobes of the cerebral cortex are assigned different tasks. For example, the temporal or temporal lobe (lobus temporalis) is responsible for hearing, smell, and speech. The parietal lobe (Lobus parietalis) converts signals for taste perception and touch. The posterior lobe or occipital lobe (lobus occipitalis) is active in vision and the frontal lobe or frontal lobe (lobus frontalis) is responsible for movement, thought processes and speech. In many cases, the cerebral cortex is also divided into two further lobes: the so-called insular lobe (lobus insularis) and the limbic lobe (lobus limbicus). The former handles the processing of chemical stimuli through smell and taste, as well as crucial tasks in the sense of balance. The latter is crucial in the development of emotions and drive behavior and controls the release of endorphins, which can have pain-relieving and euphoria-producing effects. In the cortex, signals from the sensory organs are processed into coherent impressions and perceptions of the environment with the help of upstream brain regions. The majority of the signals received from the sensory organs are switched by the neurons located in the thalamus and transmitted to the respective “higher” region of the cortex for “translation” into a coherent perception. The cerebral cortex is also responsible for storing information, thus forming the biological basis of our memory. Reason and thinking, goal-oriented action and the emergence of feelings, are all products of the processes in our cerebral cortex.

Diseases and disorders

Our sensory perception is subject to a complex interplay between the cerebral cortex and sensory organs.If the area in the cortex responsible for a particular sensory organ is damaged, sensory perception may be disturbed or completely absent despite a functioning sensory organ. For example, if the visual center in the cerebral cortex is damaged, blindness may occur despite fully functioning eyes. If certain higher level areas of the cortex are affected, the person can see but cannot convert what he sees into useful information. Thus, due to local disturbances, he is, for example, unable to recognize or distinguish faces. Damage in the lowest turn of the frontal lobe may result in limitations of speech, but often not of speech comprehension. Injuries in the anterior part of the frontal lobe can cause personality changes or reduce intelligence. A widespread and unfortunately as yet incurable disease affecting the cerebral cortex is Alzheimer’s disease. In Alzheimer’s patients, protein proteins known as neurofibrils are deposited in the nerve cells of the cortex. These proteins disrupt transport processes in the affected cells, leading to the death of the nerve cells as the disease progresses. Initially, the areas responsible for memory and cognitive abilities are mostly affected, whereby Alzheimer’s often makes itself felt through frequent forgetfulness. Damage to the cerebral cortex can vary greatly in severity and symptoms due to the high complexity and sensitivity of the brain, and is the subject of ongoing medical research.