After studying this chapter, you should be able to:
- Describe the various forms of memory.
- Identify the parts of the brain involved in memory processing and storage.
- Define synaptic plasticity, long-term potentiation (LTP), long-term depression (LTD), habituation, and sensitization, and their roles in learning and memory.
- Describe the abnormalities of brain structure and function found in Alzheimer disease.
- Define the terms categorical hemisphere and representational hemisphere and summarize the difference between these hemispheres.
- Summarize the differences between fluent and nonfluent aphasia, and explain each type on the basis of its pathophysiology.
A revolution in our understanding of brain function in humans has been brought about by the development and widespread availability of positron emission tomographic (PET), functional magnetic resonance imaging (fMRI), computed tomography (CT) scanning, and other imaging and diagnostic techniques. PET is often used to measure local glucose metabolism, which is proportional to neural activity, and fMRI is used to measure local amounts of oxygenated blood. These techniques provide an index of the level of the activity in various parts of the brain in completely intact healthy humans and in those with different diseases or brain injuries (see Clinical Box 15–1). They have been used to study not only simple responses but complex aspects of learning, memory, and perception. Different portions of the cortex are activated when hearing, seeing, speaking, or generating words. Figure 15–1 shows examples of the use of imaging to compare the functions of the cerebral cortex in processing words in a male versus a female subject.
Clinical Box 15–1
Traumatic Brain Injury
Traumatic brain injury (TBI) is defined as a nondegenerative, noncongenital insult to the brain due to an excessive mechanical force or penetrating injury to the head. It can lead to a permanent or temporary impairment of cognitive, physical, emotional, and behavioral functions, and it can be associated with a diminished or altered state of consciousness. TBI is one of the leading causes of death or disability worldwide. According to the Center for Disease Control, each year at least 1.5 million individuals in the United States sustain a TBI. It is most common in children under age 4, in adolescents aged 15–19 years of age, and in adults over the age of 65. In all age groups, the incidence of TBI occurrence is about twice as high in males compared to females. In about 75% of the cases, the TBI is considered mild and manifests as a concussion. Adults with severe TBI who are treated have a mortality rate of about 30%, but about 50% regain most if not all of their functions with therapy. The leading causes of TBI include falls, motor vehicle accidents, being struck by an object, and assaults. In some cases, areas remote from the actual injury also begin to malfunction, a process called diaschisis. TBI is often divided into primary and secondary stages. Primary injury is ...
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