To create pictures of the outside world, the brain divides up the incoming visual input and sends it to separate cortical areas for the processing of color, movement, shape, and shading—as we will see in more detail in Chapter 3. But the occipital lobes don’t do all this work alone. As we noted previously, they coordinate with adjacent areas in the parietal lobes to locate objects in space. They also work with temporal regions to produce visual memories (Ishai & Sagi, 1995; Miyashita, 1995). To complete the picture, we should note that congenitally blind people recruit the visual cortex to help them read Braille (Amedi et al., 2005; Barach, 2003).
The Association Cortex In accomplishing its magnificent feats of multitasking, our brain relies both on the “primary processing areas” of the cortex as well as the “association areas” of the cortex. The association cortex, named for the belief that complex thinking relies upon associating ideas with each other, actually constitutes more than half of the cerebral cortex. But before these associations are made, specific areas of the cortex must process the raw data streaming in from the sense organs: For example, the primary visual cortex processes raw visual stimulation, such as the let- ters in a word and whether any are capitalized. Then the association area takes over to interpret the meaning of the message, such as perceiving the whole of the word or sentence. Thus, diverse parts of the association cortex, throughout our lobes, interpret sensations, lay plans, make decisions, and prepare us for action— precisely the mental powers in which we humans excel and that distinguish us from other animals.
The Cooperative Brain No single part of the brain, however, takes sole responsi- bility for emotion, memory, personality, or any other complex psychological char- acteristic: There are no single “brain centers” for any of our major faculties. Rather, every mental and behavioral process involves the coordination and cooperation of many brain networks, each an expert at some highly specialized task (Damasio, 2003; LeDoux, 2002). For example, when you do something as simple as answer a ringing telephone, you hear it in your temporal lobes, interpret its meaning with the help of the frontal lobes, visually locate it with your occipital and parietal lobes, initiate grasping the phone on the orders of your frontal and parietal lobes, and engage in thoughtful conversation, again using frontal and temporal lobe circuitry. And the cortex cannot do its work without communicating with circuits lying deep beneath the surface: the limbic system, thalamus, brain stem, cerebellum, and other structures.
Clearly, the brain usually manages to “put it all together” in a coordinated effort to understand and respond to the world. Exactly how it does so is not clear to neuro- scientists—and, in fact, constitutes one of the biggest mysteries of modern psychology. Some clues have appeared in recent work, however. Constantly active, even when we are asleep, our brains produce pulses of coordinated waves sweeping over the cortex that are thought, somehow, to coordinate activity in far-flung brain regions (Buzsáki, 2006). All these busy neural networks work in elegant coordination with each other in work and in play, in waking and sleeping, from conception to death—and mostly without our awareness.
Cerebral Dominance Throughout our discussion of various brain structures and their associated functions, we have made some distinctions between functions in the left and right hemispheres. We know, for example, that a person with injury to the right hemi- sphere would probably not experience language difficulties but could have trouble with spatial orientation—for example, feeling lost in a familiar place or unable to complete a simple jigsaw puzzle. This tendency for each hemisphere to take the lead in different tasks is called cerebral dominance, an often-exaggerated concept. While it is true that some processes are more under the control of the left hemisphere and others are predominantly right-hemisphere tasks, both hemispheres continu- ally work together to produce our thoughts, feelings, and behaviors—courtesy of association cortex Cortical regions throughout the brain that combine information from various other parts of the brain.