A psychologist is diagnosing a patient and wants to measure the patient's prefrontal brain metabolism levels while the patient is told to concentrate on her obsessions. The psychologist uses fMRI to measure prefrontal brain metabolism levels before,

. She finds that her patient's concentration on obsessions is correlated with increases in prefrontal brain metabolism levels, and she concludes that her patient has obsessive-compulsive disorder. Discuss the grounds on which such a conclusion would be criticized, and describe what else the psychologist might do to diagnose her patient.

Answer: Physiological assessment is not sufficient because (1) any individual autonomic response has a low correlation with other autonomic responses; (2) individuals vary in their reactivity, and for some, thinking about obsessions may be associated with great increases in prefrontal brain activity while for others, there may be no increase; and (3) some people with OCD do not exhibit increased metabolism rates in the prefrontal cortex, while others without OCD do exhibit increased metabolism in this brain region. The psychologist's assessment of her patient's condition could include (1) other physiological measures; (2) the psychologist's observations of her patient; (3) measures from some form of rating scale or self-report inventory.