Answer to Question 1
The current DSM-5 is based on a categorical system. It attempts to treat mental disorders as physical disorders. It assumes that there are disease entities, such as schizophrenia, unipolar depression, OCD, etc., that are discrete, that are caused by a specific etiological process, and that are qualitatively different from each other. The DSM lays out the behaviors and signs to look for and then spells out when to assign an individual to a discrete category. If the DSM were a dimensional system, such as intelligence, it would assume that an individual was possessed of various properties and assign each individual an estimate of how much of a given property they demonstrate. An individual may demonstrate a significant level of delusional thinking, somewhat less intellectual impairment, varying degrees of unhappiness, etc. This system may or may not result in a definitive or categorical diagnosis.
Answer to Question 2
fMRI
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The cardiovascular system.
The respiratory system.
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