FUNCTIONAL ORGANIZATION OF THE CEREBRAL CORTEX

Specific types of sensory, motor, and integrative signals areprocessed in certain cerebral regions Generally,sensory areas receive and interpret sensory impulses, motorareas initiate movements, and association areas deal with morecomplex integrative functions such as memory, emotions, reasoning,will, judgment, personality traits, and intelligence.

Sensory Areas (posterior half of both cerebral hemispheres)

The following are some important sensory areas (the areanumbers referenced below are the Brodmann numbers discussedin Figure Sensory impulses arrive mainly in the posterior half of both cerebral hemispheres, in regions behind the central sulci.

primary sensory areas receive sensory information that has been relayed through lower regions of the brain from peripheral sensory receptors.

Secondary sensory areas and sensoryassociation areas often are adjacent to the primary areas. They usually receive input both from the primary areas and from other brain regions.

A person with damage in the primary visual area wouldbe blind in at least part of his visual field, but a person with damageto a visual association area might see normally yet be unable torecognize a friend.

• The primary somatosensory area (areas 1, 2, and 3) is locateddirectly posterior to the central sulcus of each cerebral hemispherein the postcentral gyrus of each parietal lobe. The primary somatosensory area receives nerve impulses fortouch, proprioception (joint and muscle position), pain, itch,tickle, and thermal sensations. The size of the cortical area receiving impulsesfrom a particular part of the body depends on the number of receptorspresent there rather than on the size of the body partThe major function of the primary somatosensory area isto pinpoint the areas where sensations originate, so that youknow exactly where on your body to swat at that mosquito.

• The primary visual area (area 17), located at the posterior tipof the occipital lobe mainly on the medial surface (next to thelongitudinal fissure), receives visual information and is involvedin visual perception.

• The primary auditory area (areas 41 and 42), located in thesuperior part of the temporal lobe near the lateral cerebral sulcus,receives information from auditory receptors and is involvedin auditory perception.

• The primary gustatory area (area 43), located at the baseof the postcentral gyrus superior to the lateral cerebral sulcus inthe parietal cortex, receives impulses for taste and is involved ingustatory perception.

• The primary olfactory area (area 28), located on the medialaspect of the temporal lobe (and thus not visible in receives impulses for smell and is involved in olfactoryperception.

Motor Areas(anterior part)

Motor output from the cerebral cortex flows mainly from theanterior part of each hemisphere. Among the most importantmotor areas are the following figure

• The primary motor area (area 4) is located in the precentralgyrus of the frontal lobe. Each region in the primary motorarea controls voluntary contractions of specific muscles or groups of muscles Electrical stimulation ofany point in the primary motor area causes contraction of specificskeletal muscle fibers on the opposite side of the body. More cortical area is devoted to those muscles involved inskilled, complex, or delicate movements. For instance, the corticalregion devoted to muscles that move the fingers is muchlarger than the region for muscles that move the toes.

• Broca’s speech area (areas 44 and 45) is located inthe frontal lobe close to the lateral cerebral sulcus. Speakingand understanding language are complex activities that involveseveral sensory, association, and motor areas of the cortex. Inabout 97 percent of the population, these language areas arelocalized in the left hemisphere. The planning and productionof speech occur in the left frontal lobe in most people. FromBroca’s speech area, nerve impulses pass to the premotorregions that control the muscles of the larynx, pharynx, andmouth. The impulses from the premotor area result in specific,coordinated muscle contractions. Simultaneously, impulsespropagate from Broca’s speech area to the primarymotor area. From here, impulses also control the breathingmuscles to regulate the proper flow of air past the vocal cords.The coordinated contractions of your speech and breathingmuscles enable you to speak your thoughts.

People who suffera cerebrovascular accident (CVA) or stroke in this area can stillhave clear thoughts, but are unable to form words, a phenomenonreferred to as nonfluent aphasia

Cerebral palsy (CP) is a motor disorder that results in theloss of muscle control and coordination; it is caused by damage ofthe motor areas of the brain during fetal life, birth, or infancy. Radiationduring fetal life, temporary lack of oxygen during birth,and hydrocephalus during infancy may also cause cerebral palsy.

Association Areas (motor and sensory areas)

Association areas are connected with one anotherby association tracts

• The somatosensory association area (areas 5 and 7) is justposterior to and receives input from the primary somatosensoryarea, as well as from the thalamus and other parts of the brain.

This area permits you to determine the exact shape and textureof an object without looking at it, to determine the orientationof one object with respect to another as they are felt, and tosense the relationship of one body part to another. Another roleof the somatosensory association area is the storage of memoriesof past sensory experiences, enabling you to compare currentsensations with previous experiences. For example, the somatosensoryassociation area allows you to recognize objectssuch as a pencil and a paperclip simply by touching them.

• The prefrontal cortex (frontal association area) is an extensivearea in the anterior portion of the frontal lobe that is welldevelopedin primates, especially humans (areas 9, 10, 11, and12; area 12 is not illustrated since it can be seen only in a medialview). This area has numerous connections with otherareas of the cerebral cortex, thalamus, hypothalamus, limbicsystem, and cerebellum. The prefrontal cortex is concernedwith the makeup of a person’s personality, intellect, complexlearning abilities, recall of information, initiative, judgment,foresight, reasoning, conscience, intuition, mood, planning forthe future, and development of abstract ideas. A person withbilateral damage to the prefrontal cortices typically becomesrude, inconsiderate, incapable of accepting advice, moody,inattentive, less creative, unable to plan for

the future, and incapableof anticipating the consequences of rash or recklesswords or behavior.

• The visual association area (areas 18 and 19), located in theoccipital lobe, receives sensory impulses from the primary visualarea and the thalamus. It relates present and past visualexperiencesand is essential for recognizing and evaluating whatis seen. For example, the visual association area allows you torecognize an object such as a spoon simply by looking at it.

• The auditory association area (area 22), located inferior andposterior to the primary auditory area in the temporal cortex,allows you to recognize a particular sound as speech, music, ornoise.

• Wernicke’s (posterior language) area (VER-ni-ke-z) (area22, and possibly areas 39 and 40), a broad region in the lefttemporal and parietal lobes, interprets the meaning of speechby recognizing spoken words. It is active as you translatewords into thoughts. The regions in the right hemisphere thatcorrespond to Broca’s and Wernicke’s areas also contribute toverbal communication by adding emotional content, such asanger or joy, to spoken words. Unlike those who have CVAs inBroca’s area, people who suffer strokes in Wernicke’s area canstill speak, but cannot arrange words in a coherent fashion.

• The common integrative area (areas 5, 7, 39, and 40) is borderedby somatosensory, visual, and auditory association areas.It receives nerve impulses from these areas and from the primarygustatory area, primary olfactory area, the thalamus, andparts of the brain stem. This area integrates sensory informationfrom the association areas and impulses from other areas,allowing the formation of thoughts based on a variety ofsensory inputs. It then transmits signals to other parts of thebrain for the appropriate response to the sensory signals it hasinterpreted.

• The premotor area (area 6) is a motor association area that isimmediately anterior to the primary motor area. Neurons inthis area communicate with the primary motor cortex, the sensoryassociation areas in the parietal lobe, the basal nuclei, andthe thalamus. The premotor area deals with learned motoractivities of a complex and sequential nature. It generates nerve

impulses that cause specific groups of muscles to contract in aspecific sequence, as when you write your name. The premotorarea also serves as a memory bank for such movements.

• The frontal eye field area (area 8) in the frontal cortex issometimes included in the premotor area. It controls voluntaryscanning movements of the eyes—like those you just usedin reading this sentence.

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