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A major tenet of the neurosciences has been that all neurons

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Re: A major tenet of the neurosciences has been that all neurons [#permalink]

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New post 08 May 2012, 09:39
Got 3 and 6 wrong in 10 min.
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Re: A major tenet of the neurosciences has been that all neurons [#permalink]

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New post 04 Feb 2013, 21:13
This post received
Purpose and Main Idea: To suggest that current thinking about vertebrate (especially human) neurogenesis needs to be modified in light of research into canary brains. The author’s main idea is that the results of this research both defy the existing theory about vertebrate neurogenesis and open up the possibility that human brains may have the capability to regenerate themselves.

Paragraph Structure: ¶1 outlines the traditional theory that vertebrate neurogenesis basically doesn’t exist—that an adult vertebrate’s brain cannot create new nerve cells. The Contrast Keyword “However” (line 10) signals that the passage is about to provide some evidence to the contrary and, predictably, ¶s 2 and 3 go on to discuss in detail the behavioral and neurological evidence (from canaries) that throws the accuracy of the traditional theory into question. In ¶4, the author addresses the implications of these research findings for humans. The Contrast Keyword “Although” (line 48) serves to distinguish the general scientific community’s skeptical response from the author’s much more optimistic stance that human brains may be able to regenerate themselves.
The Big Picture:
A good grasp of a passage doesn’t mean assimilating all of its details (you can look them up if you have to). It means understanding what the author’s doing in the text—in this case, understanding that the author’s taking issue with the traditional theory of vertebrate neurogenesis (and its implications for the human brain) by providing evidence that contradicts it.
While the author’s specific main idea isn’t entirely clear until you’ve read through the whole passage, topic, scope, and purpose are all revealed early—by line 12.

1. (A) The only choice consistent with the author’s topic, scope, and purpose. (B) focuses on a detail. Moreover, the author suggests that there’s no difference between canary brains and the brains of other vertebrates in this respect—if he believed otherwise, why would he suggest that research findings about canary brains have implications for vertebrate neurogenesis in general? (C) The author asserts precisely the opposite. Canary research breaks with the traditional theory of vertebrate neurogenesis, and supplies clues as to how researchers may discover neurogenesis in the human brain. (D) and (E) have scope problems: To be an acceptable response, (D) should have limited itself to “ supply of vertebrate brain cells,” not the overly broad “supply of brain cells,” while (E) should have confined itself to “older hypotheses about vertebrate neurogenesis,” not the more encompassing “older hypotheses.” Both choices have other problems as well. (D) is too categorical; the author’s more cautious in his conclusions. As for (E), the author never states that vertebrates other than canaries are subject to a “yearly cycle.”

2. (D) Lines 21-24 say that the canary’s singing ability decreases during the late summer and fall. Lines 35-38 attribute this seasonal decrease to a 38% drop in the number of neurons in those parts of the brain that control singing. This is simply another way of saying that those regions of the brain decrease in size during the late summer and fall. (A) Au contraire: Lines 24-27 and 32-33 indicate that the canary’s song repertoire matures in the spring. (B) Au contraire aussi: The new song-learning neurons are generated during the winter and spring months. (C) distorts the text: Canaries do learn a new repertoire of songs (during the winter and spring), but there’s no indication that these songs are based on the songs of fellow canaries. (E) Canaries largely lose their ability to sing during the late summer and fall, after which they learn “entirely new” (line 27) songs for the next breeding season.

3. (B) The ratio of brain weight to body weight is mentioned as a possible explanation for neurogenesis in canaries only. This ratio has no direct connection per se to the larger issue of general vertebrate neurogenesis, and certainly not to human neurogenesis in particular. (A) The author’s entire argument rests on the supposition that humans, like canaries, may have the capability to generate new nerve cells; thus, it’s safe to infer that he’d consider research on neurological similarities to be important. (C) The author alludes to the importance of studying infant neurogenesis in lines 54-58. (D) The importance of understanding how long-term memory works in order to determine the possible effects of neurogenesis on long-term memory is suggested in lines 52-54. (E) Similarly, the author suggests in lines 52-54 that it’s important to understand how complex learning takes place in order to figure out the possible effects neurogenesis might have on complex learning.

4. (C) If it were true that birds similar to the canary have bigger brains, the author’s explanation for canary neurogenesis would be placed in jeopardy. In ¶3, after all, he argues that canary neurogenesis occurs because the canary needs to possess a lot of information in order to sing, yet has a small brain adapted for flight. Hence its brain, with its limited storage capacity, has to generate new nerve cells every year in order for it to relearn how to sing. (A) is consistent with the author’s explanation. He suggests that canary neurogenesis is spurred in part by the canary’s long lifetime. (B) The author’s basic explanation, which rests on the link between limited brain capacity and neurogenesis cycles, isn’t fundamentally threatened by cyclic differences from species to species. (D) has no impact on the author’s explanation, as he draws no link between the ability to sing and the ability to fly. (E) is consistent with the author’s explanation, which suggests that singing ability is directly related to brain size.

5. (D) Lines 12-13 draw a comparison between the way canaries learn to sing and the way humans learn to speak. Thus, the word “vocabulary” is meant to evoke a sense of this similarity by applying a concept taken from human speech to canary song. (A) echoes the substance of the detail rather than addressing why the author included it in the text. (B) and (E) go way too far. Indeed, the author never even discusses “patterned groupings of sounds” in canary songs or “the syllabic structures of words” (B). Nor does the text compare the level of complexity of canary song and human speech (E). (C) goes against the text, which reveals that canary songs are anything but stable and uniform over the course of the bird’s lifetime. Lines 19-27, in fact, stress just the opposite of what (C) says.

6. (A) Lines 40-42 explicitly state that a long life span may help to account for canary neurogenesis. (B)-(E) mention subjects that are connected in some way to canary neurogenesis, but none of them is ever described as a possible cause of same.

7. (C) Beginning in line 10, the author discusses “new evidence for neurogenesis.” Furthermore, this new evidence “might help uncover a mechanism” (line 50) to promote human neurogenesis, despite the fact that “neurogenesis in the adult mammalian brain is still not generally accepted” (lines 48-49). Based on these sentiments, it’s clear that the author believes that the “current understanding of neurogenesis” is “incomplete.” (A) and (B) express sentiments that are the opposite of the author’s. According to him, the traditional view of neurogenesis is neither comprehensive (A), nor forward-thinking (B). (D) and (E), on the other hand, take the author’s view to an unwarranted extreme. “Incomplete” is not the same thing as “antiquated” (D) or “incorrect” (E).
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Re: A major tenet of the neurosciences has been that all neurons [#permalink]

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New post 08 Apr 2015, 07:07
Hello from the GMAT Club VerbalBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: A major tenet of the neurosciences has been that all neurons [#permalink]

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New post 13 Apr 2015, 12:44
13 mins- 28 seconds for me. Got 7 correct. Need to increase my speed.

I sometimes fall prey to the tempting wrong answers and happened on one occassion this time. Arrrgh...

lahoosaher wrote:
A major tenet of the neurosciences has been that all neurons (nerve cells) in the brains of vertebrate animals are formed early in development. An adult vertebrate, it was believed, must make do with a fixed number of neurons: those lost through disease or injury are not replaced, and adult learning takes place not through generation of new cells but through modification of connections among existing ones.

However, new evidence for neurogenesis (the birth of new neurons) has come from the study of canary song. Young canaries and other songbirds learn to sing much as humans learn to speak, by imitating models provided by their elders. Several weeks after birth, a young bird produces its first rudimentary attempts at singing; over the next few months the song becomes more structured and stable, reaching a fully developed state by the time the bird approaches its first breeding season. But this repertoire of song is not permanently learned. After each breeding season, during late summer and fall, the bird loses mastery of its developed “vocabulary,” and its song becomes as unstable as that of a juvenile bird. During the following winter and spring, however, the canary acquires new songs, and by the next breeding season it has developed an entirely new repertoire.

Recent neurological research into this learning and relearning process has shown that the two most important regions of the canary’s brain related to the learning of songs actually vary in size at different times of the year. In the spring, when the bird’s song is highly developed and uniform, the regions are roughly twice as large as they are in the fall. Further experiments tracing individual nerve cells within these regions have shown that the number of neurons drops by about 38 percent after the breeding season, but by the following breeding season, new ones have been generated to replace them. A possible explanation for this continual replacement of nerve cells may have to do with the canary’s relatively long life span and the requirements of flight. Its brain would have to be substantially larger and heavier than might be feasible for flying if it had to carry all the brain cells needed to process and retain all the information gathered over a lifetime.

Although the idea of neurogenesis in the adult mammalian brain is still not generally accepted, these findings might help uncover a mechanism that would enable the human brain to repair itself through neurogenesis. Whether such replacement of neurons would disrupt complex learning processes or long-term memory is not known, but songbird research challenges scientists to identify the genes or hormones that orchestrate neurogenesis in the young human brain and to learn how to activate them in the adult brain.
1. Which one of the following best expresses the main idea of the passage?
(A) New evidence of neurogenesis in canaries challenges an established neurological theory concerning brain cells in vertebrates and suggests the possibility that human brains may repair themselves.
(B) The brains of canaries differ from the brains of other vertebrate animals in that the brains of adult canaries are able to generate neurons.
(C) Recent studies of neurogenesis in canaries, building on established theories of vertebrate neurology, provide important clues as to why researchers are not likely to discover neurogenesis in adult humans.
(D) Recent research into neurogenesis in canaries refutes a long-held belief about the limited supply of brain cells and provides new information about neurogenesis in the adult human brain.
(E) New information about neurogenesis in canaries challenges older hypotheses and clarifies the importance of the yearly cycle in learning processes and neurological replacement among vertebrates.
[Reveal] Spoiler:

2. According to the passage, which one of the following is true of the typical adult canary during the late summer and fall?
(A) The canary’s song repertoire takes on a fully structured and stable quality.
(B) A process of neurogenesis replaces the song-learning neurons that were lost during the preceding months.
(C) The canary begins to learn an entirely new repertoire of songs based on the models of other canaries.
(D) The regions in the canary’s brain that are central to the learning of song decrease in size.
(E) The canary performs slightly modified versions of the songs it learned during the preceding breeding season.
[Reveal] Spoiler:

3. Information in the passage suggests that the author would most likely regard which one of the following as LEAST important in future research on neurogenesis in humans?
(A) research on possible similarities between the neurological structures of humans and canaries
(B) studies that compare the ratio of brain weight to body weight in canaries to that in humans
(C) neurological research on the genes or hormones that activate neurogenesis in the brain of human infants
(D) studies about the ways in which long-term memory functions in the human brain
(E) research concerning the processes by which humans learn complicated tasks
[Reveal] Spoiler:

4. Which one of the following, if true, would most seriously undermine the explanation proposed by the author in the third paragraph?
(A) A number of songbird species related to the canary have a shorter life span than the canary and do not experience neurogenesis.
(B) The brain size of several types of airborne birds with life spans similar to those of canaries has been shown to vary according to a two-year cycle of neurogenesis.
(C) Several species of airborne birds similar to canaries in size are known to have brains that are substantially heavier than the canary’s brain.
(D) Individual canaries that have larger-than-average repertoires of songs tend to have better developed muscles for flying.
(E) Individual canaries with smaller and lighter brains than the average tend to retain a smaller-than-average repertoire of songs.
[Reveal] Spoiler:

5. The use of the word “vocabulary” (line 23) serves primarily to
(A) demonstrate the presence of a rudimentary grammatical structure in canary song
(B) point out a similarity between the patterned groupings of sounds in a canary’s song and the syllabic structures of words
(C) stress the stability and uniformity of canary’s song throughout its lifetime
(D) suggest a similarity between the possession of a repertoire of words among humans and a repertoire of songs among canaries
(E) imply that the complexity of the canary’s song repertoire is equal to that of human language
[Reveal] Spoiler:

6. According to the passage, which one of the following factors may help account for the occurrence of neurogenesis in canaries?
(A) the life span of the average canary
(B) the process by which canaries learn songs
(C) the frequency of canary breeding seasons
(D) the number of regions in the canary brain related to song learning
(E) the amount of time an average canary needs to learn a repertoire of songs
[Reveal] Spoiler:

7. Which one of the following best describes the organization of the third paragraph?
(A) A theory is presented, analyzed, and modified, and a justification for the modification is offer.
(B) Research results are advanced and reconciled with results from other studies, and a shared principle is described.
(C) Research results are presented, further details are provided, and a hypothesis is offered to explain the results.
(D) Research results are reported, their implications are explained, and an application to a related field is proposed.
(E) Research results are reported, their significance is clarified, and they are reconciled with previously established neurological tenets.
[Reveal] Spoiler:

8. It can be inferred from the passage that the author would most likely describe the current understanding of neurogenesis as
(A) exhaustive
(B) progressive
(C) incomplete
(D) antiquated
(E) incorrect
[Reveal] Spoiler:


Kudos to you, for helping me with some KUDOS.

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Re: A major tenet of the neurosciences has been that all neurons [#permalink]

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New post 20 Apr 2015, 23:55
Easy passage and even easier question. I am getting strangely comfortable with veritas RCs.



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Re: A major tenet of the neurosciences has been that all neurons   [#permalink] 20 Apr 2015, 23:55

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