Handbook of Functional Neuroimaging of Cognition

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  In the late spring of 1998, a conference was held in the wonderful and rustic town of Banff, Alberta, situated deep in the heartland of the Canadian Rockies. There, overthe course of three days and two nights, cognitive neuroscientists gathered to discussand argue about issues that concerned the functional neuroimaging of cognitiveprocesses. A great deal of data was presented, and a plethora of views were advanced.At times, people were convinced by the data and interpretations being put forward,but just as often, people were skeptical. So, the discussions and arguments wouldbegin again. All in all, it was tremendous fun, and a very stimulating weekend!Now, typically that would be the end of the story. Usually, when a intense meetingcomes to a close, the participants brush themselves off, pick up their things, and headoff for home; more tired than when they first arrived, and, hopefully, a little wiser aswell.But this conference would prove to be very different. The discussions and argu-ments had highlighted to all that there was a very real need to put together a book onthe functional neuroimaging of cognition.This book would have to do at least twothings. It would have to provide a historical perspective on the issues and imagingresults in a number of different cognitive domains. And for each domain, it wouldhave to articulate where things stood currently, and where they might be heading.That is the goal of the present handbook.The handbook was written with two types of readers in mind: those who are rela-tively new to functional neuroimaging and/or cognitive neuroscience, and those whoare seeking to expand their understanding of cognitive and brain systems. It is ourhope, and intention, that this unique combination of depth and breadth will renderthe book suitable for both the student and the established scientist alike. With a bal-anced blend of theoretical and empirical material, the handbook should serve as anessential resource on the functional neuroimaging of cognitive processes, and on thelatest discoveries obtained through positron emission tomography (PET) and func-tional magnetic resonance imaging (fMRI). Indeed, in recent years the field of func-tional neuroimaging of cognition has literally exploded. From less than a dozenpapers in 1994, the number of publications in this area increased to about 70 in 1995,and to more than 300 in 1999 (Cabeza & Nyberg, 2000, Journal of Cognitive Neuro-science , 12, 1–47). This handbook provides the reader with a comprehensive but con-cise account of this rapidly growing literature.During its rapid development, functional neuroimaging has transformed itself sev-eral times, in terms of methods, topics of research, and subject populations.Thehandbook reviews and evaluates the progress of functional neuroimaging researchalong these three dimensions. The first part covers the history and methods of PETand fMRI, including physiological mechanisms (chapter 1), event-related paradigms(chapter 2), and network analysis techniques (chapter 3). The second part covers PET Preface  and fMRI findings in specific cognitive domains: attention (chapter 4), visual recog-nition (chapter 5), semantic memory (chapter 6), language (chapter 7), episodic mem-ory (chapter 8), and working memory (chapter 9). The third and final part addressesthe effects of aging on brain activity during cognitive performance (chapter 10) andresearch with neuropsychologically impaired patients (chapter 11).We are grateful to a great number of individuals who had a part in making thishandbook a reality. Michael Gazzaniga supported our idea for this book and broughtit to the attention of Michael Rutter at The MIT Press. Michael Rutter and KatherineAlmeida have been instrumental in all phases of development of this project from itsinitiation to the production of the volume. And, of course, the authors needed tocarry the project forth. In editing this handbook, we had substantial help from several anonymous reviewers, and generous support from the Alberta HeritageFoundation for Medical Research. Last but not least, we are thankful to our wives fortheir love, patience, and support. viiiPreface  Marcus E. RaichleINTRODUCTION Since 1990 cognitive neuroscience has emerged as a very important growth area inneuroscience. Cognitive neuroscience combines the experimental strategies of cog-nitive psychology with various techniques to examine how brain function supportsmental activities. Leading this research in normal humans are the new techniques of functional brain imaging: positron emission tomography (PET) and magnetic reso-nance imaging (MRI), along with event-related potentials (ERPs) obtained from elec-troencephalography (EEG) or magnetoencephalography (MEG).The signal used by PET is based on the fact that changes in the cellular activity of the brain of normal, awake humans and unanesthetized laboratory animals are invari-ably accompanied by changes in local blood flow (for a review see Raichle, 1987). This robust, empirical relationship has fascinated scientists for well over a century,but its cellular basis remains largely unexplained despite considerable research.More recently it has been appreciated that these changes in blood flow are accom-panied by much smaller changes in oxygen consumption (Fox & Raichle, 1986; Foxet al., 1988). This leads to changes in the actual amount of oxygen remaining in bloodvessels at the site of brain activation (i.e., the supply of oxygen is not matched pre-cisely with the demand). Because MRI signal intensity is sensitive to the amount of oxygen carried by hemoglobin (Ogawa et al., 1990), this change in blood oxygen con-tent at the site of brain activation can be detected with MRI (Ogawa et al., 1992;Kwong et al., 1992; Bandettini et al., 1992; Frahm et al., 1992).Studies with PET and MRI and magnetic resonance spectroscopy (MRS) havebrought to light the fact that metabolic changes accompanying brain activation donot appear to follow exactly the time-honored notion of a close coupling betweenblood flow and the oxidative metabolism of glucose (Roy & Sherrington, 1890; Siesjo,1978). Changes in blood flow appear to be accompanied by changes in glucose uti-lization that exceed the increase in oxygen consumption (Fox et al., 1988; Blomqvistet al., 1994), suggesting that the oxidative metabolism of glucose may not supply all of the energy demands encountered transiently during brain activation. Rather,glycolysis alone may provide the energy needed for the transient changes in brainactivity associated with cognition and emotion.Because of the prominent role of PET and MRI in the study of human brain func-tion in health and disease, it is important to understand what we currently knowabout the biological basis of the signals they monitor. Individuals using these tools orconsidering the results of studies employing them should have a working knowledge 1 Functional Neuroimaging: A Historical and Physiological Perspective
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