PrepTest 155, Section 4, Question 3
Researcher: Newly formed neurons can help to heal(54 more words not shown)
If the researcher's statements are(10 more words not shown)
- ANewly formed neurons(15 more words not shown)
- BNewly formed neurons(14 more words not shown)
- CMidsized spiny neurons(18 more words not shown)
- DIn cases of(14 more words not shown)
- EIn most cases(13 more words not shown)
Reading the argument
The new neurons have to become the right kind. Just producing more neurons isn't enough. Think of an injured area where type A is the most common neuron. Under the researcher's rule, new neurons can help heal that area only if they develop into type A. If they become type B instead, they fail the requirement. The letters are just placeholders to make the rule easier to follow.
Now apply it to the striatum. The most common type there is the midsized spiny neuron, but the newly formed neurons never develop into that type when the striatum is injured. They don't become what they would need to become to help with the injury.
What we’re looking for
So we can predict that these newly formed neurons won't help heal the injured striatum. Be careful about going further: the researcher hasn't said that new neurons are the only possible way to heal an injury. The brain might recover through some other process. The must-be-true answer should stay with what this particular process cannot do.
Working the answers
- A
We don't know what newly formed neurons become in other parts of the brain. They might become midsized spiny neurons elsewhere, or they might not. The facts about what happens in an injured striatum don't settle either possibility.
- B
How soon do new neurons appear, and how commonly do they appear after injuries? We aren't told. The researcher describes what newly formed neurons would need to become to help and what happens in the striatum. That doesn't establish that new neurons commonly appear shortly after an injury rather than much later.
- C
Midsized spiny neurons are the most common type in the striatum. That doesn't make the striatum the only place where they could be the most common type. We have no comparison with the neuron populations in other brain areas.
- DCorrect
Helping heal this injury requires becoming the most common type of neuron in the injured area. In the striatum, that means becoming midsized spiny neurons. The new neurons never become that type, so they cannot help heal the injury. This matches our prediction without claiming that healing by every other means is impossible.
- E
We know about injuries to one part of the brain, not the distribution of brain injuries overall. Striatum injuries could be rare or could account for a large share of injuries; the passage doesn't say. We therefore cannot extend the result for this particular area to most cases of brain injury.
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