A major tenet of the neurosciences has been that all neurons

Question

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 
 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.

2 
 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.

3 
 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

4 
 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.

5 
 5. The use of the word “vocabulary” ( Highlighted ) 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

6 
 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

7 
 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.

8 
 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

GC14 · Accepted Answer

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).

jawele · Answer

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?
Relevant text: 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.
(A) research on possible similarities between the neurological structures of humans and canaries if neurological structures of humans were not similar to that of canaries, then conclusions drawn from the findings from canary research would less likely be applicable to the study of human brain neurogenesis - stays in
(B) studies that compare the ratio of brain weight to body weight in canaries to that in humans correct: both are vertebrate, but mammals are different from birds, so such research would unlikely be helpful
(C) neurological research on the genes or hormones that activate neurogenesis in the brain of human infants stays in
(D) studies about the ways in which long-term memory functions in the human brain stays in
(E) research concerning the processes by which humans learn complicated tasks stays in

4. Which one of the following, if true, would most seriously undermine the explanation proposed by the author in the third paragraph?
Relevant text: 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 <...>
(A) A number of songbird species related to the canary have a shorter life span than the canary and do not experience neurogenesis. falls out of the scope of research
(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. goes in line with the research
(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. correct
(D) Individual canaries that have larger-than-average repertoires of songs tend to have better developed muscles for flying. got myself in trouble with this one: I assumed that larger-than-average repertoires of song translates into heavier brain (more information = more brain cells, a trend that matches the seasonality) and that having better developed muscles countered the idea that the canary would not be able to fly; so this would seem to weaken that larger brains account for the neurogenesis as such a problem seemingly can be overcome; nevertheless, COULD ANYBODY PLEASE POINT OUT THE EXACT RESEAN WHY D IS WRONG?
(E) Individual canaries with smaller and lighter brains than the average tend to retain a smaller-than-average repertoire of songs. seems to go in line with the research: less in information -> less brain cells -> smaller brains

6. According to the passage [ detail question type, and not a strengthen type ], which one of the following factors may help account for the occurrence of neurogenesis in canaries?
Relevant text: 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 [ two things ].
(A) the life span of the average canary correct
(B) the process by which canaries learn songs "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 <...>" - the process helped to spot the finding but not in itself helps to explain the neurogenesis
(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

Could anyone please comment on option D in Q4? I have given my reasoning above.

Thank you

u1983 GMATNinja SajjadAhmad workout GMATNinjaTwo Gnpth

GMATNinja · Answer

In the third paragraph, the author proposes that "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." His/her reasoning behind this explanation is that the canary's 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. " Now take another look at (D): You are correct to point out that more songs could lead to a bigger brain, which is supported by the fact that the big brained birds also have better developed muscles. However, does this undermine the author's proposed explanation? He/she argued that a canary couldn't carry around "all the information gathered over a lifetime." (D) does not specify that canaries with "larger-than-average repertoires of songs" actually remember all of the songs they ever learned -- they just remember more songs than average. The fact that remembering more songs leads to a bigger brain actually supports the author's explanation, because it adds more evidence to the connection between brain size and the amount of information in the canary's brain. Because (D) doesn't show that canaries can compensate for a brain holding "all the information gathered over a lifetime" by developing muscle, it does not undermine the author's explanation. I hope that helps! (And interesting that this LSAT passage is about neurogenesis in canaries, and so is this GMAT SC question . Seems like somebody is borrowing ideas from other exams...

)

auradediligodo · Answer

Hi everyone,
Got 7/8 correct in 17 minutes.

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P1

Paragraph one describes a milestone of neuroscience. Such principle states that the number of neurons is established in the age of development and once the adult age is reached, nothing can be done in cases of losses of neurons. Plus the learning process in adult vertebrates is not given by replacement of neurons but by changes among the connections of neurons

Brief summary:  A neuroscience milestone about neurons

P2

Paragraph 2 is in clear contrast with paragraph 1. Some evidence coming from the field of neuroscience seems to contradict the standard theory presented in P1.
The study presented is about canary's singing. The canary learns how to sing like a human being learns how to speak. But the learning is not permanent. There is a yearly cycle according to which by the breeding season a canary has learnt a new repertoire of songs and by the end of summer/beginning of fall such repertoire is almost forgotten.

Brief summary:  New evidence from neuroscience

P3

Paragraph 3 acts as a bridge between P1 and P2. In P2 in fact, we are not given that the number of neurons drops or is regenerated. In paragraph 3 we know that, according to a recent experiment, the areas of the brain associated with learning (in canaries) change in size in different times of the year. Specifically the brain is bigger during the breeding season and it is smaller during summer/fall. Furthermore, the number of neurons drops after each breeding seasons and is regenerated before such seasons.
Lastly we are given the reasons that justify such results: lifespan and problems associated with flying. In fact, the birds brain would be too heavy if it kept all the information recollected over a life time.

Brief summary:  Experiments result and justifications of results

P4

In paragraph 4 we are given that what neurogenesis proved is still not completely accepted but there are some advantages for future applications. There might be drawbacks in such applications such as the disruption of complex learning processes but the results are also challenging for scientists since now they can investigate which hormones an which genes are responsible for the regeneration of neurons in the human brain.

Brief summary:  future applications for neurogenesis

Main point

The main point is to describe the results of neurogenesis and to challenge a long held theory

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1. Which one of the following best expresses the main idea of the passage?

Pre-thinking

Main point question

Refer to main point and summaries above

(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.
 In line with pre-thinking

(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.
 We are not given comparisons between canaries and other animals

(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.
 The author in the end suggests that the results from neurogenesis can help scientists to investigate neurogenesis in the human brain

(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.
 The importance of the yearly cycle is not clarified in general but only for the canaries

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2. According to the passage, which one of the following is true of the typical adult canary during the late summer and fall?

Pre-thinking

Detail question

From P2: "  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.  "

From P3: "   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.  "

(A) The canary’s song repertoire takes on a fully structured and stable quality.
 Opposite

(B) A process of neurogenesis replaces the song-learning neurons that were lost during the preceding months.
  Opposite

(C) The canary begins to learn an entirely new repertoire of songs based on the models of other canaries.
 The canary starts to forget actually

(D)   The regions in the canary’s brain that are central to the learning of song decrease in size.
 In line with pre-thinking

(E) The canary performs slightly modified versions of the songs it learned during the preceding breeding season.
 Out of scope

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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?

Pre-thinking

Inference question

Since so many options could be irrelevant let's try through the POE to eliminate the relevant options and what will be left will be out choice.

(A) research on possible similarities between the neurological structures of humans and canaries
 This option is quite relevant since the goal of the study is to apply the findings to the research on the human brain. Out

(B)   studies that compare the ratio of brain weight to body weight in canaries to that in humans
 The comparison between the two brains seems quite irrelevant. This option is a good candidate to be the right answer

(C) neurological research on the genes or hormones that activate neurogenesis in the brain of human infants
 In the last paragraph we are given that scientists are be challenged to investigate such areas in humans. out

(D) studies about the ways in which long-term memory functions in the human brain
 This option is relevant because long term memory is discussed in relation to canaries

(E) research concerning the processes by which humans learn complicated tasks
 definitely relevant. out

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4. Which one of the following, if true, would most seriously undermine the explanation proposed by the author in the third paragraph?

Pre-thinking

Weaken question

From P3: "   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.   "

We need to weaken either the long life span aspect or the requirements of flight.

(A) A number of songbird species related to the canary have a shorter life span than the canary and do not experience neurogenesis.
 This option seems to strengthen the argument. Out

(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.
 Whether the cycle is a yearly cycle or not it does not impact the argument

(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.
 This option weakens the aspect related to the requirements of flight. If neurogenesis serves primarily to reduce the size of the brain of birds when they needs to migrate then stating that some other birds can travel with a bigger brain definitely weakens the argument

(D) Individual canaries that have larger-than-average repertoires of songs tend to have better developed muscles for flying.
 This option does not impact the argument since such birds's brain will anyhow reduce

(E) Individual canaries with smaller and lighter brains than the average tend to retain a smaller-than-average repertoire of songs.
 This option strengthen the argument. out

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5. The use of the word “vocabulary” (Highlighted) serves primarily to

Pre-thinking

Purpose question

The purpose is to establish a similarity between humans and canaries in the sense that as humans talk canaries sing

(A) demonstrate the presence of a rudimentary grammatical structure in canary song
 Not in line with pre-thinking

(B) point out a similarity between the patterned groupings of sounds in a canary’s song and the syllabic structures of words
 Not in line with pre-thinking

(C) stress the stability and uniformity of canary’s song throughout its lifetime
 Not in line with pre-thinking

(D)   suggest a similarity between the possession of a repertoire of words among humans and a repertoire of songs among canaries
 in line with pre-thinking

(E) imply that the complexity of the canary’s song repertoire is equal to that of human language
 Not in line with pre-thinking

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6. According to the passage, which one of the following factors may help account for the occurrence of neurogenesis in canaries?

Pre-thinking

Detail question

From P3: "   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.  "

(A)   the life span of the average canary
 in line with pre-thinking

(B) the process by which canaries learn songs
 Not in line with pre-thinking

(C) the frequency of canary breeding seasons
 Not in line with pre-thinking

(D) the number of regions in the canary brain related to song learning
 Not in line with pre-thinking

(E) the amount of time an average canary needs to learn a repertoire of songs
 Not in line with pre-thinking

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7. Which one of the following best describes the organization of the third paragraph?

Pre-thinking

Structure question

Results are presented and possible explanations are given

(A) A  theory  is presented, analyzed, and  modified , and a justification for the modification is offer.
 Not in line with pre-thinking

(B) Research results are advanced and  reconciled with results from other studies , and a shared principle is described.
 Not in line with pre-thinking

(C)   Research results are presented, further details are provided, and a hypothesis is offered to explain the results.
 in line with pre-thinking

(D) Research results are reported, their implications are explained, and an application to a related field is proposed.
 Not in line with pre-thinking

(E) Research results are reported, their significance is clarified, and they are reconciled with previously established neurological tenets.
 Not in line with pre-thinking

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8. It can be inferred from the passage that the author would most likely describe the current understanding of neurogenesis as

Pre-thinking

Inference question

From P4: "  Although the idea of neurogenesis in the adult mammalian brain is still not generally accepted,  "

(A) exhaustive
 Opposite

(B) progressive
 Nowhere we can infer this statement

(C)   incomplete
 If the studies are still not accepted they might be incomplete. Plus Such studies should challenge scientists to investigate more so we cannot conclude that they are incorrect

(D) antiquated
 Nowhere we can infer this statement

(E) incorrect
 Nowhere we can infer this statement

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It is a good day to be alive!

Hoozan · Answer

GMATNinja   SajjadAhmad   auradediligodo  I have doubts regarding Q4 and Q8

Q4] While I understood why (C) makes sense please could you help me understand (D)

4. Which one of the following, if true, would most seriously undermine the explanation proposed by the author in the third paragraph?

P3:-  "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."

Pre-thinking:-  I read the above and tried solving it like a CR argument. So what could weaken the above? What if the wings of the bird are strong enough to carry the heavy brain? In that cause "flight requirements" can be weakened

Now look at (D)

(D) Individual canaries that have larger-than-average repertoires of songs tend to have better developed muscles for flying.

Understanding:-  If the canaries have a larger repertories of songs, it means it will need a larger brain to store information. And if these birds already have a strong muscular pair of wings then no need to reduce the size of the brain (in line with pre-thinking)

Q8] Please help me understand why (B) is incorrect?

8. It can be inferred from the passage that the author would most likely describe the current understanding of neurogenesis as

P4:-  "these findings might help uncover a mechanism that would enable the human brain to repair itself through neurogenesis."

Pre-thinking:-  Words such as "findings might help uncover" give a positive and futuristic view to the current neurogenesis. So why isn't this "progressive"

Sajjad1994 · Answer

Why (D) is wrong in question #4

Try to differentiate between ability to fly and ability to sing  (D)  has no impact on the author’s explanation, as he draws  no link  between the  ability to sing and the ability to fly.

Why (B) is wrong in question #8

Beginning in first line of para 2  (However, new evidence for neurogenesis) , the author discusses  “new evidence for neurogenesis.”  Furthermore, this new evidence  “might help uncover a mechanism”   (In the start of last para)  to promote human neurogenesis, despite the fact that  “neurogenesis in the adult mammalian brain is still not generally accepted”  (First two lines of last para). Based on these sentiments, it’s clear that the author believes that the  “current understanding of neurogenesis”  is  “incomplete.”

(B)  express sentiments that are the opposite of the author’s. According to him, the traditional view of neurogenesis is neither comprehensive, nor forward-thinking and hence  (B) is wrong.

Natansha · Answer

Hi  GMATNinja   KarishmaB  could you please explain how (C) is the right option, it says '' Several species of airborne birds similar to canaries in size are known to have brains that are substantially heavier than the canary’s brain'', these other species could be showing neurogenesis as well and replacing cells to maintain flight, we don't know anything about it, D still seems a better option over C as it seems too vague

GMATNinja · Answer

Question 4 
 
"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." - The idea is that if the canaries brains were significantly larger and heavier, then the birds would have trouble flying. So maybe that's why they shed neurons every year.

But choice (C) is evidence that the birds would NOT have trouble flying if their brains were larger and heavier. If other, similarly-sized birds can fly with heavier brains, then the canaries should be able to as well.

Whether those other birds shed/regenerate neurons is irrelevant. Either way, if (C) is true, then those birds "are   known   to have brains that are substantially heavier than the canary’s brain." Again, if those birds can fly with substantially heavier brains, then the author's theory doesn't make as much sense: why shed neurons to save brain weight if the extra brain weight likely isn't an issue for flying?

I hope that helps!

A major tenet of the neurosciences has been that all neurons

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GMAT Reading Comprehension (RC) Questions

A major tenet of the neurosciences has been that all neurons

Prep Toolkit

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

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards