Handbook Of Functional Neuroimaging Of Cognition 2nd ed - Roberto Cabeza, Psychologia po angielsku
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Preface
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, over
the course of three days and two nights, cognitive neuroscientists gathered to discuss
and argue about issues that concerned the functional neuroimaging of cognitive
processes. 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 would
begin 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 meeting
comes to a close, the participants brush themselves off, pick up their things, and head
off for home; more tired than when they first arrived, and, hopefully, a little wiser as
well. 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 on
the functional neuroimaging of cognition. This book would have to do at least two
things. It would have to provide a historical perspective on the issues and imaging
results in a number of different cognitive domains. And for each domain, it would
have 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 who
are seeking to expand their understanding of cognitive and brain systems. It is our
hope, and intention, that this unique combination of depth and breadth will render
the 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 an
essential resource on the functional neuroimaging of cognitive processes, and on the
latest 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 dozen
papers 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. The
handbook reviews and evaluates the progress of functional neuroimaging research
along these three dimensions. The first part covers the history and methods of PET
and fMRI, including physiological mechanisms (chapter 1), event-related paradigms
(chapter 2), and network analysis techniques (chapter 3). The second part covers PET
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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 addresses
the effects of aging on brain activity during cognitive performance (chapter 10) and
research with neuropsychologically impaired patients (chapter 11).
We are grateful to a great number of individuals who had a part in making this
handbook a reality. Michael Gazzaniga supported our idea for this book and brought
it to the attention of Michael Rutter at The MIT Press. Michael Rutter and Katherine
Almeida have been instrumental in all phases of development of this project from its
initiation to the production of the volume. And, of course, the authors needed to
carry the project forth. In editing this handbook, we had substantial help from
several anonymous reviewers, and generous support from the Alberta Heritage
Foundation for Medical Research. Last but not least, we are thankful to our wives for
their love, patience, and support.
1
Functional Neuroimaging: A Historical and Physiological Perspective
Marcus E. Raichle
INTRODUCTION
Since 1990 cognitive neuroscience has emerged as a very important growth area in
neuroscience. Cognitive neuroscience combines the experimental strategies of cog-
nitive psychology with various techniques to examine how brain function supports
mental 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; Fox
et al., 1988). This leads to changes in the actual amount of oxygen remaining in blood
vessels 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) have
brought to light the fact that metabolic changes accompanying brain activation do
not appear to follow exactly the time-honored notion of a close coupling between
blood 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; Blomqvist
et 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 brain
activity 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 know
about the biological basis of the signals they monitor. Individuals using these tools or
considering the results of studies employing them should have a working knowledge
4
Marcus E. Raichle
of their biological basis. This chapter reviews that information, which is, at times,
conflicting and incomplete.
While it is easy to conclude that much of this work transpired since 1990 or so be-
cause of its recent prominence in the neuroscience literature, in truth work on these rela-
tionships and the tools to exploit them has been developing for more than a century. In
order to place present work in its proper perspective, a brief historical review of work
on the relationships between brain function, blood flow, and metabolism is included.
Before beginning, it is useful to consider the intended goal of functional localiza-
tion with brain imaging. This may seem self-evident to most. Nevertheless, interpre-
tations frequently stated or implied about functional imaging data suggest that, if one
is not careful, functional brain imaging could be viewed as no more than a modern
version of phrenology.
It is Korbinian Brodmann (Brodmann, 1909) whose perspective I find appealing.
He wrote: “Indeed, recently theories have abounded which, like phrenology, attempt
to localize complex mental activity such as memory, will, fantasy, intelligence or spa-
tial qualities such as appreciation of shape and position to circumscribed cortical
zones.” He went on to say, “These mental faculties are notions used to designate
extraordinarily involved complexes of mental functions. One cannot think of their
taking place in any other way than through an infinitely complex and involved inter-
action and cooperation of numerous elementary activities. In each particular case
[these] supposed elementary functional loci are active in differing numbers, in differ-
ing degrees and in differing combinations. Such activities are always the result of the
function of a large number of suborgans distributed more or less widely over the cor-
tical surface” (for these English translations see Garey, 1994: 254–255).
With this prescient admonition in mind, the task of functional brain imaging be-
comes clear: identify regions and their temporal relationships associated with the per-
formance of a well-designed task. The brain instantiation of the task will emerge from
an understanding of the elementary operations performed within such a network. The
great strength of functional brain imaging is that it is uniquely equipped to undertake
such a task and can do so in the brain of most interest to us, the human brain.
FUNCTIONAL NEUROIMAGING: A HISTORICAL AND PHYSIOLOGICAL
PERSPECTIVE
Historical Background
The quest for an understanding of the functional organization of the normal human
brain, using techniques to assess changes in brain circulation, has occupied man-
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