The cerebral cortex makes up about 75% of the human brain. It is made up of several layers of cells and is about 1/8th of an inch thick. This thin collection of cell layers, however, is very tightly folded, somewhat like a crumpled sheet of paper, so that a large amount of it takes up only a small amount of space. Activity in the cerebral cortex is essential for many of the qualities, skills, and abilities that make humans different from all other animals. In fact, if you lost your cerebral cortex, you would lose your self-awareness, your ability to respond with foresight and deliberation to the environment, your ability to relate your past and future to the present, your ability to speak and understand language, and many other higher functions. Humans born without much of a cerebral cortex are capable of only the most basic reflexes and emotions, and they tend not to live very long. Humans who have damage to more limited parts of the cerebral cortex show problems with the skills and abilities associated with those parts. Greg, for example, had significant amounts of damage to parts of his cerebral cortex — damage that made him seem to be a “hollowed-out” version of a human being: he lost much of his former personality, seemed to have little awareness of himself, and tended to treat others interchangeably (Sacks, 1995). These deficits resulted in Greg’s inability to engage in normal human social interactions.
The cerebral cortex (and, in fact, most of the rest of the brain) is divided into two hemispheres (“half-spheres”), one on each side of the head. In the cerebral cortex, activity within each hemisphere is associated with different functions. This localization of different mental and behavioral functions within each hemisphere is referred to as laterality of functioning. In most people, for example, the ability to produce language is associated with activity in the left hemisphere of the cerebral cortex (see Sections 3-9 and 3-10).
Sensation and Perception
All animals rely very heavily on their senses — sight, hearing, touch, taste, and smell — when adapting themselves to their environments. Sensory information enters the body through sensory receptors in the eyes, ears, skin, bodily joints, tongue, and nose. This information then travels through the PNS, which sends most of it first into the spinal cord, where some processing of the sensory information begins, and then up into the brain, where more complex processing occurs. The most complex processing of sensory information occurs in the cerebral cortex, which is the part of the brain most responsible for our ability to consciously perceive the world around us. The term sensation refers to the activation of the nervous system by stimuli (light, sound waves, odor chemicals, etc.). These stimuli activate sensory receptors in the sense organs (eyes, ears, etc.), which activate nerves in the PNS leading away from these receptors, which activate parts of the CNS involved in processing sensory information. The term perception, on the other hand, refers to the conscious, preconscious, or unconscious recognition (interpretation) of these stimuli — a recognition that is the end-product of the processing of sensory information during sensation. In other words, we will use sensation to refer to biological processes (the activation of cells in the PNS and CNS) and perception to refer to cognitive (mental) processes.
The senses of sight, hearing, and touch are each associated primarily with activity in areas of the cerebral cortex referred to as lobes. Each hemisphere of the cerebral cortex can be separated into four lobes: the frontal, parietal, occipital, and temporal lobes (see Figure 1). The frontal lobes are behind the eyes and forehead and extend across the front half of the top of the head; the parietal lobes are on the back half of the top of the head; the occipital lobes are in the back of the head; and the temporal lobes are on the sides of the head around the ears. Studies of the major functions of each of these lobes began in the second half of the nineteenth century. A wide variety of techniques have been used to gain knowledge about these functions: case studies of people with brain damage, experimental lesioning of brains in animals, electrical stimulation of brains in animals and humans, and so on. In much of the rest of Chapter 3, you will learn about the results of this research.
Study Questions for Section 3-6
- The cerebral cortex makes up about what proportion of the human brain?
Damage to the cerebral cortex causes what kinds of problems in humans?
What is meant by the term “laterality of functioning”?
How are sensations similar to and different from perceptions?
What are the four major lobes of the brain and where are they located?
Sacks, O. (1995). An anthropologist on Mars: Seven paradoxical tales. New York: Knopf.