Throughout the twentieth century, it was accepted as fact that cells in our brains, called neurons, do not regenerate. Research by neurologist Elizabeth Gould overturned this core doctrine within the span of a few years. Her experiments on rats showed that even after suffering severe trauma, their brains were able to heal themselves by regenerating neurons. Gould’s findings have incited a flood of new research into applications that may take advantage of neurogenesis.

One such study examines the role of reduced neurogenesis among individuals suffering from depression. It is speculated that neurogenesis may contribute to an explanation for the so called “Prozac lag.” As an antidepressant, the immediate boost of serotonin caused by Prozac should have had instantaneous mood elevating effects. However, patients suffering from depression only begin to experience mood elevation weeks after beginning treatment. The study speculates that during this period, the brain may be regenerating neurons.

The author mentions the “Prozac lag” primarily in order to

A) raise a possible objection to a newly proposed theory
B) present a situation for which a new theory may serve an explanatory role
C) offer evidence that runs counter to a previously held belief
D) suggest a counterexample that undermines a newly proposed theory
E) provide supporting evidence that a newly discovered phenomenon may have unforeseen effects



In the second paragraph, select the sentence in which the author describes an unexpected observation.