Logical Reasoning

PT141 · S4 · Q20 In a recent study of

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In a recent study of stroke patients, those who exhibited continuing deterioration of the nerve cells in the brain after the stroke also exhibited the highest levels of the protein glutamate in their blood.

Conclusion

Glutamate leaking from damaged or oxygen-starved nerve cells is a cause of long-term brain damage resulting from strokes.

Evidence

If glutamate leaks from damaged or oxygen-starved nerve cells, glutamate can kill surrounding nerve cells.

In a study of stroke patients, there was a correlation between those with long-term brain damage and those with highest levels of glutamate in their blood.

Evaluate

Since the evidence involves a study with a correlation (people who were X had the highest levels of Y) and the conclusion involves causality (Y is a cause of X), we can use our Curious Fact / Explanation template.

Curious Fact Why did the stroke patients with the long term damage to their brain's nerve cells have the highest levels of glutamate in their blood? Author's Explanation Glutamate leaked from damaged or oxygen-starved nerve cells and killed surrounding nerve cells.

We now start asking questions like - can we think of some Alternate Explanation for why the patients with brain damage had high levels of glutamate in their blood? - how plausible is the Author's Explanation?

With correlations, we usually consider Alternate Explanations like reverse causality or third factor.

Is it possible the brain damage came first, and the high glutamate level came second? Seems hard to argue in that fashion, but maybe something else caused the deteriorating nerve cells, and once the damage had been done, the glutamate leaked out into the brain.

Could there be some third factor that is separately causing both? Sure, maybe, there's some underlying genetic trait that makes these patients more likely to suffer from brain damage and high glutamate levels.

In terms of the plausibility of the author's explanation, it would help the author's story if we established that these patients with brain damage could have had damaged or oxygen-starved nerve cells. It would also help to know that the high glutamate level came before the brain damage.

The most common way to strengthen causality is No Cause, No Effect, so we might see an answer that says

Goal

Find an answer that rules out a different explanation for the correlation between "continuing deterioration and high glutamate" or that adds some plausibility to the author's explanation.

20.

Which one of the following, if true, most strengthens the argument?

Any neurotransmitter that leaks from
Weakens, if Anything
We didn't need to be convinced that glutamate will damage surrounding nerve cells (we had already been told that), so this is really only opening up the possibility of alternate causes, if there are other neurotransmitters that also could be the culprit in causing this brain damage.
12% picked this
Stroke patients exhibit a wide
No Impact
A "wide variety of abnormal chemicals in their blood" is too unspecific to do anything. At worst, this is actually nudging in a weaken direction by suggesting that there might be other possible chemical levels that are off, and one of those might be causing the brain damage.
2% picked this
Glutamate is the only neurotransmitter
No Impact
This is better than nothing, kind of, although we really don't care if other neurotransmitters leak. We'd only care if the other neurotransmitters were known to kill nerve cells (then they would be a potential alternate cause).
31% picked this
Correct
Leakage from damaged or oxygen-starved
Why this is right
"the only" is a sufficient condition indicator (unlike "only / only if" which are both necessary indicators). Glutamate it leaked from damaged or in the blood ? oxygen-starved nerve cells We now know that the stroke patients in this study, the ones that had the highest levels of glutamate, definitely got that because glutamate leaked from damaged or oxygen-starved nerve cells. Wait, didn't we already know that? [Check the text] No, sneaky-sneaky. It was phrased as a conditional, with the if trigger hidden by putting it later in the sentence. If glutamate leaks, then the glutamate can kill nearby nerve cells. But in these stroke patients, did the glutamate leak? We were never told it did. Obviously, in order for the author's brain damage story to be correct, he's assuming that some glutamate leaked out of struggling nerve cells. This answer strengthens by establishing that assumption, as well as simultaneously ruling out all other possible explanations for having glutamate in the blood.
Skill tested: Strengthen · how this choice captures the argument's function is the move to repeat next time.
50% picked this
Nerve cells can suffer enough
Irrelevant / Weak
Stuff as weakly worded as "some, can, may, sometimes" is almost always wrong on Strengthen, Weaken, Paradox. It's irrelevant to this argument whether the leaky cells are also killed. The author is only counting on glutamate killing surrounding cells.
5% picked this

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