Hockenbury Discovering Psychology 5th txtbk

34 CHAPTER 1 Introduction and Research MethodsFOCUS ON NEUROSCIENCEPsychological Research Using Brain ImagingBrain-scan images have become so commonplace in news articlesand popular magazines that it’s easy to forget just how revolutionarybrain-imaging technology has been to the field ofpsychology (Cacioppo & others, 2008). Here, we’ll look at threecommonly used brain-imaging techniques and how they’re usedin psychological research.Positron emission tomography, abbreviated PET, is basedon the fact that increased activity in a particular brain region isassociated with increased blood flow and energy consumption.A small amount of radioactively tagged glucose, oxygen, orother substance is injected into the person’s bloodstream. Then,the person lies in a PET scanner while performing some mentaltask. For several minutes, the PET scanner tracks the amounts ofradioactive substance used in thousands of different brain regions.A computer analyzes the data, producing color-coded imagesof the brain’s activity.Magnetic resonance imaging (MRI) does not involve invasiveprocedures such as injections of radioactive substances. Instead,while the person lies inside a magnetic tube, powerfulbut harmless magnetic fields bombard the brain. A computeranalyzes the electromagnetic signals generated by brain tissuemolecules in response to the magnetic fields. The result is a seriesof digital images, each a detailed “slice” of the brain’sstructures. MRI scans are routinely used in medicine to producedetailed images of other body parts, such as the joints, spine,or organs.Functional MRI (fMRI) combines the ability to produce a detailedimage of the brain’s structures with the capacity to trackthe brain’s activity or functioning. While the person lies in theMRI scanner, a powerful computer tracks the electromagneticsignals that are generated by changes in the brain’s metabolicactivity, such as increased blood flow to a particular brain region.By measuring the ebb and flow of oxygenated blood in thebrain, fMRI produces a series of scans that show detailed moment-by-moment“movies” of the brain’s changing activitiy inspecific structures or regions.In the study of brain activity, functional MRI has several advantagesover PET scan technology. Because fMRI is a noninvasiveprocedure and the magnetic waves are harmless, research participantscan safely undergo repeated fMRI scans. fMRI producesa much sharper image than PET scans and can detail muchsmaller brain structures. Another advantage of fMRI is that itprovides a picture of brain activity averaged over seconds ratherthan the several minutes required by PET scans.How Psychologists Use Brain-Imaging TechnologyBrain imaging is used for both descriptive and experimentalresearch. A descriptive study utilizing brain scans might comparethe brain structure or functioning of one carefully definedgroup of people with another.UnpracticedPracticedPositron Emission Tomography (PET) PET scans provide colorcodedimages of the brain’s activity. This example shows thecomparison between subjects learning a new language task(left) and performing the language task after it has been welllearned(right). Red and yellow highlight areas with the highestlevel of activity while green and blue colors indicate lowerlevels of brain activity. As you can see, the process of practicingand learning a new language task involves more anddifferent brain areas before becoming established.For example, MRI scans were used to compare London taxidrivers with matched participants who were not taxi drivers(Maguire & others, 2000, 2006). In order to be licensed, Londontaxi drivers are required to have an encyclopedic knowledgeof the city streets. The MRI scans showed that a brainstructure involved in spatial memory, the hippocampus, wassignificantly larger in the experienced taxi drivers than in thecontrol subjects (see MRI scans on the next page). And, thesize of the hippocampus was also positively correlated withthe length of time the participants had been driving taxis inLondon: the longer the individual had been driving a taxi, thelarger the hippocampus. In Chapter 2, Neuroscience and Behavior,we’ll look at how the adult human brain can change inresponse to learning and environmental influences.Brain-imaging technology can also be used in experimentalresearch (see fMRI scans on the next page). In a typical experiment,brain scans are taken while research participants are exposedto the experimental treatment or task. These scans arecompared to scans taken of control group participants. The differencesbetween the two sets of scans are assumed to be dueto the experimental treatment or condition. When multiple participantsare compared, researchers combine the results frommultiple subjects to produce a composite scan showing the averagedifferences.Limitations of Brain-Imaging StudiesImages are becoming even more detailed as brain-imagingtechnology advances. Nevertheless, brain-imaging research haspotential limitations (Racine & others, 2005; Vul & others, 2009).When you consider the results of brain-imaging studies, includingthose presented in this textbook, keep the following pointsin mind:positron emission tomography(PET scan)An invasive imaging technique that providescolor-coded images of brain activity by trackingthe brain’s use of a radio actively tagged compound,such as glucose, oxygen, or a drug.magnetic resonance imaging(MRI)A noninvasive imaging technique that produceshighly detailed images of the body’s structures andtissues using electromagnetic signals generated bythe body in response to magnetic fields.