PrepTest 106, Section 3, Question 25
The interstitial nucleus, a subregion of the brain's(71 more words not shown)
Which one of the following(8 more words not shown)
- ANo female cats(14 more words not shown)
- BMany male cats(14 more words not shown)
- CThe interstitial nuclei(20 more words not shown)
- DOf 1,000 autopsies(21 more words not shown)
- EThe hypothalamus is(18 more words not shown)
Reading the argument
What if the disease makes that part of the brain larger?
The scientific names don't change the basic problem. The interstitial nucleus is a small region within the hypothalamus. In the male cats examined after they died from disease X, that region was unusually large—as large as it generally is in female cats. We have a pattern, but we haven't established which way the explanation runs.
The author says the size determines whether male cats can contract the disease. Yet the measurements come after the cats had the disease. Perhaps disease X causes the enlargement. If so, the size could be an effect of illness rather than what made the cats able to contract it.
What we’re looking for
For a weakener, that's the route I'd first expect: evidence that the illness changes the brain region. We need to test the choices against the actual claim about male cats and disease X.
Working the answers
- A
The conclusion concerns what determines whether male cats can contract the disease. No known cases among females don't refute that claim about males, even though females generally have the larger nuclei. The argument doesn't say nucleus size alone determines disease risk in both sexes.
- B
Another disease occurring in many of the same cats doesn't explain the relationship between nucleus size and disease X. B doesn't tell us whether disease Z changes this brain region or whether it causes disease X. Without a connecting fact, the extra illness doesn't challenge the proposed explanation.
- C
This gives us a similar size-and-disease association in females. It doesn't show the direction of causation in males. Even if we used the female comparison as relevant evidence, it repeats the association rather than supplying a reason to reject the causal claim.
- D
“Larger than the average male cat” isn't necessarily as large as the nuclei generally found in females—the size reported in the diseased males. Those five healthy males might have nuclei only slightly above the male average.
Also, the conclusion concerns whether a male cat can contract disease X. A cat could be susceptible without actually catching it. So a few above-average measurements in cats that didn't contract it don't provide the clear counterexample we need.
- ECorrect
Follow both connections. The interstitial nucleus is part of the hypothalamus, and disease X is a subtype of disease Y. E says the hypothalamus is known not to be causally linked to that disease category. That directly challenges assigning a causal role to a region within it for disease X.
This isn't the reversed-cause answer I predicted. It attacks the claimed connection itself. And its wording is stronger than “no link has been found”: it says the structure is known not to be causally linked. That is evidence against the causal account, not merely an absence of supporting evidence.
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