Reading comp PrepTest 125 · Section 3 · Question 21

Topic: Science

Paragraph 1

• Paragraph note
  • Old theory/new theory
• Views, minor Meta-Structures, and the author's attitude
  • Definition of “neurons”: brain cells
  • Definition of “synapses”: gaps between neurons
  • Definition of “neurotransmitter”: A chemical that binds two neurons to deliver electrical signals
  • Old theory:
    • The brain works exclusively with electrical signals
    • But unsure how electrical signals jump between neurons
  • New theory
    • Chemicals (neurotransmitters) transfer electrical signals between neurons

Paragraph 2

• Paragraph note
  • New theory’s acceptance; recent evidence shows how it works
• Views, minor Meta-Structures, and the author's attitude
  • How neurotransmitters work:
    • The structure of receptors in neurons plays a role in converting the chemical link to an electrical signal
  • Author’s attitude: “enough evidence for a convincing explanation” (lines 29-30); “pivotal role” (line 31)

Paragraph 3

• Paragraph note
  • Specifics of how it works
• Views, minor Meta-Structures, and the author's attitude
  • Cause-and-effect relationship:
    • Receptors have a binding site and ion channel
    • The neurotransmitter binds to site, which causes the receptor changes shape and open an ion channel, which allows the electrical signal to transfer to the receiving neuron
  • Comparisons
    • The different receptors are similar enough to be a family
  • List of receptors:
    • Acetylcholine, GABA, serotonin

Paragraph 4

• Paragraph note
  • Practical application of new theory
• Views, minor Meta-Structures, and the author's attitude
  • Comparison:
    • Each receptor in family has several varieties, based on its location in the brain
  • Author’s view:
    • Can potentially use these to target medications for different diseases
  • List of conditions that new medications could heal:
    • Mood disorders, tissue damage associated with stroke, Alzheimer’s
  • Author’s attitude:
    • “medically significant” (line 50); “may be able to” (line 54); “could potentially help” (lines 57-58)

Main Point: A new theory on how the brain works supplements the old theory, showing how chemicals called neurotransmitters transmit electrical signals between neurons, a discovery that may allow researchers to design medications that can target diseases related to the brain.

Lines 1-2 - Old theory

Lines 11-14 - New theory

Lines 33-36 - How new theory works

Lines 49-52 - Practical application of new theory

Old Approach/New Approach: As soon as we read “Neurobiologists once believed” at the beginning of this passage, we should expect this science passage to fall into one of the most common Meta-Structures in this topic: the Old Approach/New Approach passage (or, if we want to tailor the Meta-Structure to this passage, Old Theory/New Theory).

Here, the old theory says that brains work “exclusively” with electrical signals. The new theory, on the other hand, says that the brain also uses chemical signals to allow these electrical signals to pass between neurons (Lines 11-19). Note that the new theory still says brains work on electrical signals, they just also use chemical signals to send those electrical signals between neurons. The rest of the passage discusses this new theory and how this chemical-aided transmission occurs, and the last paragraph goes into the medical implications of the new theory. Since the author says that this theory has gained “acceptance in the scientific community” (Lines 20-21), it should be a major focus of the main point, which is reflected in how we summarized it above.

Question/Answer: There are two places where questions are raised, and answers to those questions are presented. The first is in Lines 7-8, and it raised a question the old theory couldn’t answer. As such, it previews the new theory, which serves as the answer to that question. This Question/Answer structure is therefore already reflected in our main point. The second question is posed in Lines 21-24, and it’s related to the functioning of the process in the new theory. That process is then explored at a high level at the end of Paragraph 2 and throughout Paragraph 3, making it a key part of the main point. However, since the New Theory is already a part of our main point, we don’t have to adapt it based on this Meta-Structure.

Phenomenon/Explanation: Most science passages are about explaining a phenomenon. After all, what’s a theory but a potential explanation for an observed phenomenon? Here, the phenomenon to be explained is the working of the brain and, specifically, how neurons pass electrical signals between them. The explanation that the author and scientific community accept is that chemicals called neurotransmitters change the shape of binding sites and allow those electrical signals to pass between neurons, as we’ve noted in the discussions above.

Causality: Explanations — and science, in general — are based on causality, so the new theory and explanations noted above feature causality, and we should expect answers to be phrased around that type of language.

There is a lot of science in this passage, and a lot of words that are likely unfamiliar to the average LSAT test taker. As such, it’s going to be important for us to do two things. First, focus on the logic and Meta-Structures rather than the science. If we do that, we can answer most questions. Second, leave enough notes that we can find the relevant section for any question where we’ll need to look up details to answer a question that’s above our level of understanding!

Also, note how much our Meta-Structures line up with, reinforce, and overlap with each other. It’s still important to consider each one as you’re reading, as they define the language that we expect in the correct answers! For example, while we might be expecting Old Approach/New Approach-style answers, the same content could be framed through the Question/Answer structure, or Phenomenon/Explanation. Knowing these possible phrasings for correct answers will be important in being efficient as we work through the answers!