Biomedical Engineering Reference
In-Depth Information
To develop these interlinked concepts, this chapter will be organized in five
sections. The first section will describe one of the widely used approaches in
brain mapping, namely, functional magnetic resonance imaging (fMRI), which
has provided important insights into the neural systems in humans involved with
emotion and the processing of reward/aversion information. This type of neuro-
imaging, in conjunction with developments in the experimental psychology of
motivation described in the second section, has produced the data and ap-
proaches described in the third, fourth, and fifth sections. The second section
will serve as a bridge between the first and third sections and describe a general
model of motivation and the embedded systems for processing reward/aversion
information (i.e., via an iBM) as well as those that give rise to emotion. The
third section will describe converging evidence from human fMRI and other
neuroimaging studies, as well as physiological studies in animals, for a common
circuitry processing reward/aversion information and its component subproc-
esses. The fourth section will synthesize a body of human neuroimaging evi-
dence that argues for a dysfunction in components of this reward/aversion
circuitry in neuropsychiatric illnesses. The final section will describe how a
dense mapping of the neural systems responsible for reward/aversion function
combined with genetic and genotypic data should enable us to hone in on the
networks of genes responsible for the development and maintenance of these
neural circuits, in health and in neuropsychiatric illness. Through the use of ob-
jective quantitative measures, integrative neuroscience approaches have the po-
tential to redefine our conceptualization of neuropsychiatric illness (32).
2.
IN VIVO MEASUREMENT OF HUMAN BRAIN ACTIVITY USING
f
MRI
The majority of the data gathered over the past 15 years characterizing the
neural substrates of human motivational function has been collected via tomo-
graphic and non-tomographic brain imaging techniques. Tomographic tech-
niques that localize signal changes in three-dimensional space include: positron
emission tomography (PET), single photon emission computed tomography
(SPECT), magnetic resonance imaging (MRI), and optical imaging techniques.
Non-tomographic techniques include electroencephalography (EEG) and mag-
netoencephalography (MEG). Each of these techniques has unique benefits
that warrant its use for specific neuroscience questions (please see (251) for
technical discussion of such considerations). Functional MRI (fMRI) has been
the most widely used technique to study motivation in humans. In contrast to
studies of normative reward circuitry function, dysfunction of these systems that
contribute to neuropsychiatric illnesses has not yet been commonly studied with
fMRI. Given the ease with which fMRI acquisitions can be combined with
other forms of MRI: (1) high-resolution structural scanning for morphometric
quantitative anatomy measures (see Figure 1a), (2) arterial spin-labeling scans
for absolute resting perfusion, (3) diffusion tensor imaging for white matter trac-
tography (see Figure 1b), or (4) spectroscopy for chemical signatures related to
