Figure 1 also shows several large areas of the cerebral cortex that do not fit into the rigid categories of primary and secondary motor and sensory areas. These areas are called association areas because they receive and analyze signals simultaneously from multiple regions of both the motor and sensory cortices, as well as from subcortical structures. Yet, even the association areas have their specializations. Important association areas include (1) the parieto-occipitotemporal association area, (2) the prefrontal association area, and (3) the limbic association area.
Fig1. Locations of major association areas of the cerebral cortex, as well as primary and secondary motor and sensory areas.
Parieto-occipitotemporal Association Area
The parieto-occipitotemporal association area lies in the large parietal and occipital cortical space bounded by the somatosensory cortex anteriorly, the visual cortex posteriorly, and the auditory cortex laterally. As would be expected, it provides a high level of interpretative meaning for signals from all the surrounding sensory areas. However, even the parieto-occipitotemporal association area has its own functional subareas, which are shown in Figure 2.
Fig2. Map of specific functional areas in the cerebral cortex, showing especially Wernicke’s and Broca’s areas for language comprehension and speech production, which in 95 percent of all people are located in the left hemisphere.
Analysis of the Spatial Coordinates of the Body. An area beginning in the posterior parietal cortex and extending into the superior occipital cortex provides continuous analysis of the spatial coordinates of all parts of the body, as well as of the surroundings of the body. This area receives visual sensory information from the posterior occipital cortex and simultaneous somatosensory information from the anterior parietal cortex. From all this information, it computes the coordinates of the visual, auditory, and body surroundings.
Wernicke’s Area Is Important for Language Comprehension. The major area for language comprehension, called Wernicke’s area, lies behind the primary auditory cortex in the posterior part of the superior gyrus of the temporal lobe. We discuss this area more fully later; it is the most important region of the entire brain for higher intellectual function because almost all such intellectual functions are language based.
The Angular Gyrus Area Is Needed for Initial Processing of Visual Language (Reading). Posterior to the language comprehension area, lying mainly in the anterolateral region of the occipital lobe, is a visual association area that feeds visual information conveyed by words read from a book into Wernicke’s area, the language comprehension area. This so-called angular gyrus area is needed to make meaning out of the visually perceived words. In its absence, a person can still have excel lent language comprehension through hearing but not through reading.
Area for Naming Objects. In the most lateral portions of the anterior occipital lobe and posterior temporal lobe is an area for naming objects. The names are learned mainly through auditory input, whereas the physical natures of the objects are learned mainly through visual input. In turn, the names are essential for both auditory and visual language comprehension ( functions performed in Wernicke’s area located immediately superior to the auditory “names” region and anterior to the visual word processing area).
Prefrontal Association Area
As discussed in Chapter 57, the prefrontal association area functions in close association with the motor cortex to plan complex patterns and sequences of motor movements. To aid in this function, it receives strong input through a massive subcortical bundle of nerve fibers connecting the parieto-occipitotemporal association area with the prefrontal association area. Through this bundle, the prefrontal cortex receives much preanalyzed sensory information, especially information on the spatial coordinates of the body that is necessary for planning effective movements. Much of the output from the prefrontal area into the motor control system passes through the caudate portion of the basal ganglia–thalamic feedback circuit for motor planning, which provides many of the sequential and parallel components of movement stimulation.
The prefrontal association area is also essential to carrying out “thought” processes. This characteristic presumably results from some of the same capabilities of the prefrontal cortex that allow it to plan motor activities. It seems to be capable of processing nonmotor and motor information from widespread areas of the brain and therefore to achieve nonmotor types of thinking, as well as motor types. In fact, the prefrontal association area is frequently described simply as important for elaboration of thoughts, and it is said to store on a short-term basis “working memories” that are used to combine new thoughts while they are entering the brain.
Broca’s Area Provides the Neural Circuitry for Word Formation. Broca’s area, shown in Figure 2, is located partly in the posterior lateral prefrontal cortex and partly in the premotor area. It is here that plans and motor patterns for expressing individual words or even short phrases are initiated and executed. This area also works in close association with the Wernicke language comprehension center in the temporal association cortex, as we discuss more fully later in the chapter.
An especially interesting discovery is the following: When a person has already learned one language and then learns a new language, the area in the brain where the new language is stored is slightly removed from the storage area for the first language. If both languages are learned simultaneously, they are stored together in the same area of the brain.
Limbic Association Area
Figures 1 and 2 show still another association area called the limbic association area. This area is found in the anterior pole of the temporal lobe, in the ventral portion of the frontal lobe, and in the cingulate gyrus lying deep in the longitudinal fissure on the midsurface of each cerebral hemisphere. It is concerned primarily with behavior, emotions, and motivation. We discuss in Chapter 59 that the limbic cortex is part of a much more extensive system, the limbic system, that includes a complex set of neuronal structures in the midbasal regions of the brain. This limbic system provides most of the emotional drives for activating other areas of the brain and even provides motivational drive for the process of learning itself.
Area for Recognition of Faces
An interesting type of brain abnormality called prosopagnosia is the inability to recognize faces. This condition occurs in people who have extensive damage on the medial undersides of both occipital lobes and along the medioventral surfaces of the temporal lobes, as shown in Figure 3. Loss of these face recognition areas, strangely enough, results in little other abnormality of brain function.
Fig3. Facial recognition areas located on the underside of the brain in the medial occipital and temporal lobes. (Modified from Geschwind N: Specializations of the human brain. Sci Am 241:180, 1979.)
One may wonder why so much of the cerebral cortex should be reserved for the simple task of face recognition. However, most of our daily tasks involve associations with other people, and thus one can see the importance of this intellectual function.
The occipital portion of this facial recognition area is contiguous with the visual cortex, and the temporal portion is closely associated with the limbic system that has to do with emotions, brain activation, and control of one’s behavioral response to the environment, as we see in Chapter 59.
