REM (rapid eye movement) sleep, also called "paradoxical" sleep

Question

REM (rapid eye movement) sleep, also called "paradoxical" sleep because of its neurologically aroused character, is best known as the sleep phase during which intense dreams occur in humans. It has been found to have a surprisingly close relationship with the waking state. The electroencephalogram (EEG), which records general electrical activity in the brain, indicates that REM sleep displays high-frequency, low-amplitude waves all but identical to those of wakefulness. This is in contrast to the slow-wave (low-frequency, high-amplitude) patterns of dreamless sleep. Additionally, neurological activity in various subunits of the brain is essentially similar in both REM sleep and the awakened state. Especially revealing is a pattern of waves in a part of the cerebral cortex called the hippocampus. This "theta rhythm" is manifested regularly throughout both REM sleep and wakefulness, and it contrasts with the irregular activity of the hippocampus during slow-wave sleep. Measurements of brain temperature indicated a third similarity: brain temperature decreases slightly during slow-wave sleep, then rises in REM sleep to about the same level as in wakefulness.

A recent, accidental discovery substantially augmented our understanding of the connection. PGO spikes (short-lived, high-amplitude electrical waves observed most frequently in the pons, a region in the brain stem) were thought to occur almost uniquely in REM sleep and to occur spontaneously, without external stimulus. However, when a laboratory worker accidentally struck an EEG recording cage while a cat's slow-wave sleep was being traced, a PGO spike appeared in the record almost instantly. A subsequent study indicated that both sounds and touch could easily produce PGO spikes in either REM or slow-wave sleep. Far from being spontaneous and unique to REM sleep, PGO spikes seem to be general alerting responses occurring in several slow sleep phases.

This finding in tum has prompted a reevaluation of waves called eye-movement potentials (EMPs), which occur in the waking state. These were believed to depend on environmental levels of light, but in the EEG record, they appeared identical to PGO spikes. Reasoning that a cat in a darkened cage might be bored, a worker directed the odor of tuna fish through the cage and presently observed EMPs identical to PGO spikes. Sharp noises produced the same result. Both PGO spikes and eye movement potentials are now seen as varieties of a general alerting response, which can be stimulated during REM sleep, slow-wave sleep, and wakefulness.    1 
 1. The author is primarily concerned with

(A) proving that brain wave activity occurs during REM sleep 
(B) studying the functions of brain subunits during various sleep phases 
(C) exploring inconsistencies in current accounts of brain-wave activity in various mind states 
(D) establishing that most sleep states involve patterns of electrical activity 
(E) demonstrating the neurologically aroused character of various stages of consciousness

2 
 2. According to the passage, which of the following is true of both wakefulness and REM sleep?

(A) Slow-wave patterns predominate. 
(B) Brain temperature tends to drop. 
(C) Sensory contact with the environment is intensified. 
(D) Low-amplitude waves can be observed in the pons. 
(E) Brain wave patterns vary in response to environmental stimuli.  3

3. It can be inferred that the odor of tuna fish was directed through a darkened cage in order to determine which of the following?

(A) Do eye movement potentials occur in REM sleep? 
(B) Can EMPs occur as a response to stimuli other than environmental levels of light?
(C) Are EMPs identical to PGO spikes? 
(D) Are relaxed animals as neurologically alert as excited animals? 
(E) Do EMPs occur only in response to external stimuli?

4 
 4. The author implies that eye-movement potentials, which appear identical to PGO spikes in the EEG, were reevaluated because

(A) PGO spikes were discovered to be responses to specific external stimulation 
(B) both responses appeared randomly and spontaneously in the EEG . 
(C) EMPs had been thought to occur in the absence of external stimuli 
(D) both responses occurred only in REM sleep 
(E) neither response occurred during slow-wave sleep

jayzelenkov · Answer

Sharing my analysis of Q4.

The question is asking us to identify the cause of the reevaluation of the EMPs. EMPs are mentioned for the first time in the first sentence of the last paragraph. The paragraph starts with " This finding  in turn has prompted a reevaluation of ... (EMPs) ...".  This finding  refers to something that has already been mentioned earlier, implying the actual cause was described in the first or the second paragraph.

Answer choices:

Second paragraph says that "PGO ... were thought to occur ... spontaneously", but an accident and a subsequent study found that PGO spikes are neither spontaneous nor unique to REM: "PGO spikes seem to be general alerting responses occurring in several slow sleep phases." This could be the finding referred in the first sentence introducing EMPs. Mark this as a potential answer.

The passage says EMPs are not random and spontaneous but "... believed to depend on environmental levels of light". Cross off this answer choice.

Similar to the answer choice  B) , EMPs were "... believed to depend on environmental levels of light". Light is an example of an external (to the body) stimulus. Cross off this answer.

The third paragraph says EMPs occur in the waking state. Cross off.

The last sentence in the second paragraph says "PGO spikes seem to be general alerting responses occurring in several slow sleep phases.". Cross it off.

The only answer choice left is  A .

kanikab · Answer

GMATNinja ,  GMATNinjaTwo  - Hi could you explain this one line - The electroencephalogram (EEG), which records general electrical activity in the brain, indicates that REM sleep displays high-frequency, low-amplitude waves  all but identical to those of wakefulness .

coreyander · Answer

OFFICIAL EXPLANATION Q1:

Analyze the Question Stem:

The phrase "primarily concerned with" means this is a Global question. We want to choose an answer that encompasses the entire passage, matching the author's Purpose we noted in the passage map.

Research the Relevant Text:

The best place to go for research is our notes. We have recorded the Purpose as "To analyze the connections between various sleep stages and wakefulness by discussing the alerting response behavior of these stages."
 
Make a Prediction:

We should expect the correct answer to mention different alerting responses in the brain or different stages of sleep and wakefulness, or, at the very least, some comparison between sleep stages or alerting responses.
 
Evaluate the Answer Choices:

Choice (A) is outside the scope of the passage, because the author puts no effort toward "proving" that brain wave activity occurs during any stage of sleep; he merely states that it does occur, then uses it to support his arguments.

Choice (B) may be tempting because the passage does mention the actions of various brain subunits, but the activity of the various subunits is only used to support the main Purpose; analyzing or studying these subunits is not the Purpose itself. Eliminate.

The passage does not discuss any "inconsistencies," so choice (C) is incorrect.

Similar to choice (A), choice (D) overemphasizes "establishing" the electrical activity of sleep phases; the passage takes this activity as a given, and it does no "establishing" whatsoever. Choice (D) is also incorrect.

(E), however, does touch on the Purpose. Paragraph 1 is concerned with comparing brain activity during REM sleep to that of wakefulness, paragraph 2 shows that "PGO spikes" can occur in several stages of consciousness, and paragraph 3 discusses the stimuli that can trigger still other neurological activity. This is the correct answer.

TAKEAWAY: When answering a Global question, consult the author's purpose in writing the passage. The correct answer will align with that overall purpose and not merely reflect a supporting idea or detail.

coreyander · Answer

OFFICIAL EXPLANATION Q2:

Analyze the Question Stem:

This question stem includes the phrase "according to the passage," which means it is a Detail question. The correct answer choice will come directly from something stated in the passage.
 
Research the Relevant Text:

Wakefulness and REM sleep are discussed throughout the passage, so it's difficult to pinpoint an area for research. The best strategy is to focus on the stated similarities between REM sleep and wakefulness in paragraphs one and three.
 
Make a Prediction:

The passage states the following similarities between the two states:

1) They hold similar activity in various brain subunits (paragraph one)

2) They both manifest a "theta rhythm" (paragraph one)

3) They have similar, high brain temperatures (paragraph one)

4) They both have alerting response systems, even though the systems themselves-PGO spikes and EMPs-are slightly different (paragraph three).

The correct answer will almost certainly draw from one of these points.

Evaluate the Answer Choices:

(E) matches predicted point 4 above, and is correct. Alerting response systems are most definitely "brain wave patterns   vary in response to environmental stimuli."

(A) and (B) are actually behaviors attributed to slow-wave sleep in the first paragraph, not to REM sleep and wakefulness.

(C) might seem tempting, but nothing in the passage says that sensory contact with the environment is "intensified" in REM sleep and wakefulness in comparison to any other state; the passage merely states that alerting responses occur in all states, and doesn't say that any one is more intense than any other.

(D) is a distortion of a detail in the passage. Paragraph two says that PGO spikes occur in the pons during REM sleep, and that nearly identical waves occur during wakefulness. However, these waves are described as high-amplitude, not low-amplitude.

TAKEAWAY: Science passages are often filled with a lot of details; use the passage map to help find the right ones.

coreyander · Answer

OFFICIAL EXPLANATION Q3:  
 
Analyze the Question Stem:

The word "inferred" indicates that this is an Inference question.

Research the Relevant Text:

The question stem mentions "the odor of tuna fish," which is only mentioned in paragraph three's cat experiment.

Make a Prediction:
 
The experiment in question involved a cat in a darkened cage, and the odor of tuna fish caused brain activity in the cat that was then linked to EMPs, which were previously thought to respond only to light levels. The right answer will likely be connected to this fact.

Evaluate the Answer Choices:

(B) matches the context of the experiment quite well: EMPs were previously thought to only respond to environmental light levels, then the odor of tuna fish caused EMPs as well. It answered the question in this answer choice with a resounding "Yes." (B) is therefore correct.

(A) can't be right, because the cat was awake, not in a stage of REM sleep, during the experiment.

(C) is incorrect, because both before and after the experiment, PGOs and EMPs were seen to be virtually identical; there's no indication that the experiment was intended to prove otherwise.

(D) and (E) are also incorrect, because alertness levels and internal vs. external stimuli were neither studied nor determined by the experiment.

TAKEAWAY: Occasionally, the choices in Inference questions are presented as questions; use the passage map to help figure out which question can be answered by the passage.

coreyander · Answer

OFFICIAL EXPLANATION Q4:  
 
Analyze the Question Stem:

The phrase "author implies" means that this is an Inference question.
 
Research the Relevant Text:

The "reevaluation of…EMPs" is covered at the beginning of paragraph three. "This finding" is cited as the cause of the reevaluation, referring back to the discovery in paragraph two that PGO spikes were alerting responses.

Make a Prediction:

Atypically, this Inference question is ripe for a prediction, since the cause of the reevaluation is directly stated: the answer choice will likely mention the breakthrough concerning PGO spikes.

Evaluate the Answer Choices:

(A) stands out as a match to the prediction; it paraphrases the finding from paragraph two, which is cited in the passage as the cause for reevaluating EMPs. (A) is correct.

(B) is a false statement; paragraphs two and three state that PGO spikes and EMPs appeared in the EEG predictably in response to certain stimuli.

(C) contradicts the passage; before the cat experiment in paragraph three, EMPs were thought to occur in response to light, not "in the absence of external stimuli."

(D) is incorrect because EMPs occur "in the waking state," according to paragraph three.

(E) is incorrect because paragraph two outlines a situation in which PGO spikes were observed during slow-wave sleep periods.

TAKEAWAY: Although it's often difficult to predict in an Inference question, it's sometimes possible when the stem has a specific research clue.

coreyander · Answer

ALL BUT  --- This idiom means almost definitely.

The bill's passage is all but assured  ---- means that the bill will almost certainly pass

The above sentence means that EEG of REM displays similar properties to those of wakefulness.

VerbalBot · Answer

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REM (rapid eye movement) sleep, also called "paradoxical" sleep

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REM (rapid eye movement) sleep, also called "paradoxical" sleep

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615 to 715 in 15 Days (Ria's Strategies)

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