Biomedical Engineering Reference
In-Depth Information
face can be densely sampled with neuroimaging procedures to characterize a
particular behavioral function in a set of individuals (Figure 10a), resulting in a
quantitative representation of the neural processes necessary for that behavioral
function (e.g., the utility function relating to a set of economic goods). If multi-
ple samplings are obtained in each individual, covering defined subprocesses,
these functional (and structural) measures will define a complex set of physio-
logical and/or mechanistic interrelationships. These interrelationships can be
grouped into functionally related clusters, or systems biology maps, as is done
with cardiovascular function to produce vascular, heart, renal, endocrine, and
morphometric clusters. The physiological and/or mechanistic relationships
within such clusters, or systems biology maps, can be defined as quantitative
phenotypes. These quantitative phenotypes can be subdivided into sets of pheno-
types with different contingent probabilities for susceptibility to illness/mal-
function, or resistance to illness/malfunction.
5.
IMPLICATIONS OF REWARD
/
AVERSION NEUROIMAGING
FOR PSYCHIATRIC ILLNESS
Traditionally, major psychiatric disorders have been categorized by clusters
of patient-based reports of symptoms and behaviors observed in patients. This
phenomenological description of categorical outward signs produced the
nosology of illness based on exophenotypes that is the American Psychiatric
Associations Diagnostic Statistical Manual (DSM) (5). Neuroscientists have
recently begun to suggest approaches to replace current symptom-based charac-
terizations of illness, or exophenotypes, using a nosology based on genes, mole-
cules, neuronal organelles, and specific neural systems (60,61). Such a nosology
would potentially develop a unitary basis for psychiatric and neurological ill-
nesses. A nosology based on descriptions of brain structure and function would
also have to consider the impact of time, as many of these neuropsychiatric dis-
eases appear to have a neurodevelopmental and/or neurodegenerative compo-
nent (34,150,245). In this section, we will examine the current evidence for a
neural systems approach, focusing on alterations in reward/aversion function,
that might objectively categorize the major (i.e., Axis I disorders per DSM) neu-
ropsychiatric illnesses.
Over the past decade, studies of neuropsychiatric illness with positron emis-
sion tomography, single photon emission computed tomography, magneto-
encephalography, magnetic resonance spectroscopy, morphometric MRI, and
fMRI have begun to suggest that neuropsychiatric illnesses might be distin-
guished by alterations in circuitry structure and function (42,68). So far, no re-
search has focused on classifying the major categories of psychiatric illness on
the basis of their patterns of circuitry function or structural differences using a
unitary set of experimental paradigms or structural imaging protocols. Meta-
