Reading Comprehension

PT13 · S3 · P1 · Q4 Neuron Formation

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A major tenet of the neurosciences has been that all neurons (nerve cells) in the brains of vertebrate animals are formed early in development.

Topic

The discovery of neurogenesis (birth of new neurons) in adult canaries and its implications for neuroscience.

Framework

Old / New

Main Point

Although it was long believed that adult vertebrate brains could not generate new neurons, evidence from studies of canaries shows that adult neurogenesis does occur, which opens new possibilities for understanding and perhaps repairing the human brain. (Most valuable sentence: Final paragraph — )

P1: Traditional View in Neuroscience

For a long time, neuroscientists believed that adult vertebrate brains could not make new neurons; adults were stuck with the neurons they developed early on.

P2: Discovery Through Canary Song

Canaries learn new songs every year, losing and regaining their “vocabulary,” which suggests some sort of ongoing learning and brain change that's more dynamic than previously thought.

P3: Evidence of Neurogenesis in Canaries

Research shows that regions of the brain connected to song learning actually shrink and grow seasonally as the number of neurons decreases after breeding and then new neurons form before the next season. This likely happens because it would be impractical for a flying bird to carry all the neurons needed for a lifetime’s worth of songs.

4.

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

  1. A number of songbird species

    Strengthens, if anything

    The author thought that the long life span of the canary was part of the causal explanation for why it has this cycle of neuron-dumping followed by neurogenesis. So this answer would strengthen like a No Cause / No Effect type answer, since it's saying that species that don't have the canary's long life span don't have this cycle of neurogenesis.

    6% picked this

  2. The brain size of several

    Strengthens

    This corroborates the author's explanation in a More Cause / More Effect style. Since the author thought that a canary's long life span was part of the causal explanation for having the cycle of neurogenesis, we're adding plausibility to that story by pointing to other birds that have similar long life spans and also have a cycle of neurogenesis.

    8% picked this

  3. Correct

    Several species of airborne birds

    Why this is right

    This makes the author's explanation implausible. He was saying, "There's no way canaries could fly if they had the larger/heavier brain it would take to keep a lifetime's worth of songs up in their domes." This answer is saying, "Yes, they could. There are airborne birds similar to a canary's size that have brains that are way heavier than a canary's brain. So bigger-brain-weight would not be holding them back from flight."

    Skill tested: Weaken · how this choice captures the passage's function is the move to repeat next time.

    64% picked this

  4. Individual canaries that have larger-than-average

    Strengthens

    The author thinks that the more songs a canary has in its brain, the heavier/larger the brain will be, and the harder it would be for the canary to fly. This answer is corroborating those connections by showing that as individual canaries have abnormally large repertoires of songs weighing down their brains, they develop (or needed) stronger muscles for flying.

    18% picked this

  5. Individual canaries with smaller and

    Strengthens

    The author's explanation was kinda like this, the more songs you have in your repertoire, the bigger/heavier your brain would have to be. Another way to say the same thing is the fewer songs you have in your repertoire, the smaller / lighter your brain would have to be. And this answer is lending credence to that association.

    4% picked this

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