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OBJECTIVES

OBJECTIVES

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.

INTRODUCTION

The understanding of brain function in humans has been revolutionized by the use of positron emission tomographic (PET), functional magnetic resonance imaging (fMRI), computed tomography (CT) scanning, and other imaging and diagnostic techniques. These techniques provide an index of the level of the activity in various parts of the brain in healthy humans and in those with different diseases or brain injuries (Clinical Box 15–1). They have been used to study learning, memory, and sensory perception. Learning is acquisition of the information that makes it possible for humans to alter their behavior on the basis of experience. Memory is the retention and storage of that information. The two are closely related and are considered together in this chapter. Experience-dependent growth of new granule cells in the dentate gyrus of the hippocampus may contribute to learning and memory. Memory and learning are functions of large parts of the brain, but the centers controlling some of the other “higher functions of the nervous system” such as the mechanisms related to language are localized to the neocortex. Speech and other intellectual functions are especially well developed in humans.

CLINICAL BOX 15–1 Traumatic Brain Injury

Traumatic brain injury (TBI) is an insult to the brain due to an excessive mechanical force or penetrating injury to the head. It can lead to 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 Centers for Disease Control and Prevention, each year at least 1.5 million persons 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, TBI occurs more often in males than in females (2:1). In 75% of the cases, the TBI is mild and manifests as a concussion. Adults with severe TBI who are treated have a mortality rate of about 30%, but 50% regain most of their functions with therapy. The leading causes of TBI include falls, motor vehicle accidents, being struck by an object, and assaults. TBI can be divided into primary and secondary stages. Primary injury is that caused by the mechanical force (eg, skull ...

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