Info

Lobe

Functions

Lobe

Functions

Frontal lobes

Motor areas control movements of voluntary skeletal muscles.

Association areas carry on higher intellectual processes for concentrating, planning, complex problem solving, and judging the consequences of behavior.

Temporal lobes

Sensory areas are responsible for hearing.

Association areas interpret sensory experiences and remember visual scenes, music, and other complex sensory patterns.

Parietal lobes

Sensory areas provide sensations of temperature, touch, pressure, and pain involving the skin.

Association areas function in understanding speech and in using words to express thoughts and feelings.

Occipital lobes

Sensory areas are responsible for vision.

Association areas combine visual images with other sensory experiences.

complex sensory experiences, such as those needed to understand speech and to read. These regions also store memories of visual scenes, music, and other complex sensory patterns.

The occipital lobes have association areas adjacent to the visual centers. These are important in analyzing visual patterns and combining visual images with other sensory experiences—as when one recognizes another person.

Of particular importance is the region where the parietal, temporal, and occipital association areas join near the posterior end of the lateral sulcus. This region, called the general interpretative area (Wernicke's area), plays the primary role in complex thought processing. It receives input from multiple sensory areas and consolidates the information. This is communicated to other brain areas that respond appropriately. The general interpretive area makes it possible for a person to recognize words and arrange them to express a thought, and to read and understand ideas presented in writing. Table 11.5 summarizes the functions of the cerebral lobes.

List the general functions of the cerebrum.

Where in the brain are the primary motor and sensory regions located?

Explain the functions of association areas.

Hemisphere Dominance

Both cerebral hemispheres participate in basic functions, such as receiving and analyzing sensory impulses, controlling skeletal muscles on opposite sides of the body, and storing memory. However, in most persons, one side acts as a dominant hemisphere for certain other functions.

In over 90% of the population, for example, the left hemisphere is dominant for the language-related activities of speech, writing, and reading. It is also dominant for complex intellectual functions requiring verbal, analytical, and computational skills. In other persons, the right hemisphere is dominant, and in some, the hemispheres are equally dominant.

A person with dyslexia sees letters separately and must be taught to read in a different way than people whose nervous systems allow them to group letters into words. Three to 10% of people have dyslexia. The condition probably has several causes, with inborn visual and perceptual skills interacting with the way the child learns to read. Dyslexia has nothing to do with intelligence — many brilliant thinkers were "slow" in school because educators had not yet learned how to help them.

Tests indicate that the left hemisphere is dominant in 90% of right-handed adults and in 64% of left-handed ones. The right hemisphere is dominant in 10% of right-handed adults and in 20% of left-handed ones. The hemispheres are equally dominant in the remaining 16% of left-handed persons. As a consequence of hemisphere dominance, Broca's area on one side almost completely controls the motor activities associated with speech. For this reason, over 90% of patients with language impairment stemming from problems in the cerebrum have disorders in the left hemisphere.

How does the brain form during early development? Describe the cerebrum.

In addition to carrying on basic functions, the nondominant hemisphere specializes in nonverbal functions, such as motor tasks that require orientation of the body in space, understanding and interpreting musical patterns, and visual experiences. It also provides emotional and intuitive thought processes. For example, although the region in the nondominant hemisphere that corresponds to Broca's area does not control speech, it influences the emotional aspects of spoken language.

Nerve fibers of the corpus callosum, which connect the cerebral hemispheres, enable the dominant hemisphere to control the motor cortex of the nondominant hemisphere. These fibers also transfer sensory information reaching the nondominant hemisphere to the general interpretative area of the dominant one, where the information can be used in decision making.

Memory

Memory, one of the most astonishing capabilities of the brain, is the consequence of learning. Whereas learning is the acquisition of new knowledge, memory is the persistence of that learning, with the ability to access it at a later time. Two types of memory, short term and long term, have been recognized for many years, and researchers are now beginning to realize that they differ in characteristics other than duration.

Short-term, or "working," memories are thought to be electrical in nature. Neurons may be connected in a circuit so that the last in the series stimulates the first. As long as the pattern of stimulation continues, the thought is remembered. When the electrical events cease, so does the memory—unless it enters long-term memory.

Long-term memory probably changes the structure or function of neurons in ways that enhance synaptic transmission, perhaps by establishing certain patterns of synaptic connections. Synaptic patterns fulfill two requirements of long-term memory. First, there are enough synapses to encode an almost limitless number of memories—each of the 10 billion neurons in the cortex can make tens of thousands of synaptic connections to other neurons, forming 60 trillion synapses. Second, a certain pattern of synapses can remain unchanged for years.

Understanding how neurons in different parts of the brain encode memories and how short-term memories are converted to long-term memories (a process called memory consolidation) is at the forefront of research into the functioning of the human brain. According to one theory called long-term synaptic potentiation, primarily in an area of the cerebral cortex called the hippocampus, frequent, nearly simultaneous, and repeated stimulation of the same neurons strengthens their synap-tic connections. This strengthening results in more frequent action potentials triggered in postsynaptic cells in response to the repeated stimuli. Clinical Application 11.4 discusses some common causes of damage to the cerebrum.

Medical researchers have gained insight into the role of the hippocampus by observing the unusual behaviors and skills of people in whom these structures have been damaged. In 1953, a surgeon removed parts of the hippocampus and another area called the amygdala of a young man called H. M., thinking this drastic action might relieve his severe epilepsy. His seizures indeed became less frequent, but H. M. suffered a profound loss in the ability to consolidate short-term memories into long-term ones. As a result, events in H. M.'s life fade from memory as quickly as they occur. He is unable to recall any events that took place since surgery, living today as if it was the 1950s. He can read the same magazine article repeatedly with renewed interest each time. With practice, he improves skills that require procedural memory, such as puzzle solving. But, since factual memory is impossible, he insists that he has never seen the puzzle before!

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