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Normally, the pineal gland governs a person's sleep-wake

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Normally, the pineal gland governs a person's sleep-wake  [#permalink]

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New post 16 Sep 2018, 10:08
Official Explanation:

Argument Evaluation
Situation - Normally, a person’s sleep‐wake cycle is governed by the pineal gland secreting melatonin in response to the daily cycle of light and darkness as detected by the eye. Yet many people who are totally blind due to lesions of the visual cortex easily maintain a 24‐hour sleep‐wake cycle.

Reasoning - What additional information would be most helpful in evaluating the argument? The argument’s conclusion is that the neural pathway by which the pineal gland receives information probably does not pass through the visual cortex. This is suggested by the fact that people without a well‐functioning visual cortex (e.g., people with a certain type of blindness) can nonetheless maintain a 24‐hour sleep‐wake cycle. Is it by the pineal gland’s secretion of melatonin that they do so? The argument tells us that normally (i.e., in sighted people), this is the mechanism for sleep regulation. But the argument depends on assuming that a similar mechanism is operating in people who are blind but have well‐regulated sleep cycles. The best choice will be the one that helps us decide whether that assumption is correct.

A This question would not give us an answer that would help in evaluating the argument. A “no” answer would not clarify whether the pineal gland‐melatonin mechanism operates in people who are blind. A “yes” answer would do no better. The question refers only to people who have sleep dysfunctions (which the argument does not address).

B Correct. Answering this question would provide the most useful information for evaluating the argument. A “yes” answer would help confirm a key assumption of the argument: that blind people rely on the pineal gland‐melatonin mechanism for sleep regulation. A “no” answer would help disconfirm that assumption.

C Whether or not there are other substances secreted by the pineal gland makes no difference to the reasoning. The argument relies on the premise that the pineal gland governs the sleep cycle by secreting melatonin . For example, if the pineal gland sometimes secreted adrenaline, that would still have no bearing on the argument.

D The consistency or inconsistency of the duration of some people’s sleep patterns has no relevance to the reasoning. Their sleep patterns could be due to any of a number of factors.

E This does not help, for there could be sighted people whose melatonin levels respond abnormally simply because of a pineal‐gland abnormality.
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Normally, the pineal gland governs a person's sleep-wake  [#permalink]

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New post 16 Sep 2018, 11:41
parasena wrote:
Normally, the pineal gland governs a person's sleep-wake cycle by secreting melatonin in response to the daily cycle of light and darkness as detected by the eye. Nonetheless, many people who are totally blind due to lesions in the visual cortex of the brain easily maintain a 24-hour sleep-wake cycle. So the neural pathway by which the pineal gland receives information from the eye probably does not pass through the visual cortex.

For purposes of evaluating the argument it would be most useful to establish which of the following?

(A) Whether melatonin supplements help people who have difficulty maintaining a 24-hour sleep cycle to establish such a pattern

(B) Whether the melatonin levels of most totally blind people who successfully maintain a 24-hour sleep-wake cycle change in response to changes in exposure to light and darkness

(C) Whether melatonin is the only substance secreted by the pineal gland

(D) Whether most people who do not have a 24-hour sleep-wake cycle nevertheless have a cycle of consistent duration

(E) Whether there are any people with normal vision whose melatonin levels respond abnormally to periods of light and darkness


IMO, the correct answer should be B as it goes in line with the assumption, which can be stated as - "The melatonin secretion of a normal person and totally blind person are same"
If the secretion of melatonin is same in both of them, then they both respond to light and darkness in the same manner.
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Normally, the pineal gland governs a person's sleep-wake   [#permalink] 16 Sep 2018, 11:41

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