Hockenbury Discovering Psychology 5th txtbk

62 CHAPTER 2 Neuroscience and BehaviorThe Human Brain Weighing roughly threepounds, the human brain is about the sizeof a small cauliflower. Although your brainmakes up only about 2 percent of your totalbody weight, it uses some 20 percentof the oxygen your body needs while atrest. The oxygen is used in breaking downglucose to supply the brain with energy.One of the great conceptual leaps ofmodern neuroscience has been thenotion of neuroplasticity. . . . Scientistsnow know that even modest changesin the internal or external world canlead to structural changes in the brain.BARRY L. JACOBS (2004)brain is discussed in Science VersusPseudoscience, “Phrenology: TheBumpy Road to Scientific Progress.”Although we will identify the functionsthat seem to be associated withparticular brain regions, it’s importantto remember that specific functionsseldom correspond neatly to a single,specific brain site. Many psychologicalprocesses, particularly complex ones,involve multiple brain structures andregions. Even seemingly simpletasks—such as carrying on a conversation,catching a ball, or watching a movie—involve the smoothly coordinatedsynthesis of information among many different areas of your brain.How is information communicated and shared among these multiple brainregions? Many brain functions involve the activation of neural pathways that linkdifferent brain structures (Knight, 2007). Neural pathways are formed by groups ofneuron cell bodies in one area of the brain that project their axons to other brainareas. These neural pathways form communication networks and circuits that linkdifferent brain areas. Thus, even though we’ll talk about brain centers and structuresthat are involved in different aspects of behavior, the best way to think of thebrain is as an integrated system.functional plasticityThe brain’s ability to shift functions fromdamaged to undamaged brain areas.structural plasticityThe brain’s ability to change its physicalstructure in response to learning, activepractice, or environmental influences.neurogenesisThe development of new neurons.phrenology(freh-NOL-uh-gee) A pseudoscientific theoryof the brain that claimed that personalitycharacteristics, moral character, and intelligencecould be determined by examiningthe bumps on a person’s skull.cortical localizationThe notion that different functions arelocated or localized in different areas of thebrain; also called localization of function.The Dynamic Brain: Plasticity and NeurogenesisBefore embarking on our tour, we need to describe one last important characteristicof the brain: its remarkable capacity to change in response to experience. Until themid-1960s, neuroscientists believed—and taught—that by early adulthood the brain’sphysical structure was hard-wired or fixed for life (Raisman, 2004). But today it’sknown that the brain’s physical structure is literally sculpted by experience (Pascual-Leone & others, 2005). The brain’s ability to change function and structure isreferred to as neuroplasticity, or simply plasticity (Lledo & others, 2006). (The wordplastic originally comes from a Greek word, plastikos, that meant the quality of beingeasily shaped or molded.)One form of plasticity is functional plasticity, which refers to the brain’s abilityto shift functions from damaged to undamaged brain areas. Depending on thelocation and degree of brain damage, stroke or accident victims often need to “relearn”once-routine tasks like speaking, walking, or reading. If the rehabilitation issuccessful, undamaged brain areas gradually assume the ability to process and executethe tasks (Pascual-Leone & others, 2005).But the brain can do more than just shift functions from one area to another.Structural plasticity refers to the brain’s ability to physically change its structurein response to learning, active practice, or environmental stimulation. It is nowknown that even subtle changes in your circumstances can lead to structuralchanges in the brain (Jacobs, 2004). In the Focus on Neuroscience, “Juggling andBrain Plasticity” on page 64, we describe an ingenious experiment that dramaticallydemonstrated structural plasticity in the human brain.NeurogenesisFor many years, scientists believed that people and most animals did not experienceneurogenesis—the development of new neurons—after birth (Gross, 2000; Kaplan,2001). With the exception of birds, tree shrews, and some rodents, it was thoughtthat the mature brain could lose neurons but could not grow new ones. But newstudies offered compelling evidence that challenged that dogma (see Gould, 2007).