Q21

[LSAT on Brain]

I picked C and D is right. What it came down to is: is part of the main focus

1. enough similarities exist to be called a family (C)

or

2.the differences might allow selective treatments (D)

C is supported in line 42

D is supported in latter half of paragraph 4

It still strikes me that the treatment is not the main focus.

[ohthatpatrick]

Great analysis.

I think what you wrote is really the key to favoring (D):

C is supported in line 42

D is supported in latter half of paragraph 4

If you're wondering which ingredient carries more weight, you would be wise to consider both
1 - more time/text is dedicated to (D)
2 - the last paragraph is generally more important than the 2nd to last paragraph

Finally, it helps me to know that Science passages on LSAT often have the following structure:

i. description of an old scientific problem, quandary, puzzle, unanswered question, roadblock, or model of thinking

ii. description of recent research that moves us past that problem/roadblock and/or gives us a new model of thinking

iii. author's evaluation of the implications of this new discovery

Since the last paragraph here is stressing the significance (line 50) of what's come before it, it carries extra weight in the big picture.

Hope this helps.

[myradin]

Could you explain why answer choice A is incorrect?

[ohthatpatrick]

These answers have such tiny differences ... how annoying!!

The difference between the first half of (A)/(B) and the first half of (C)/(D) is whether the evidence shows that workings of the brain vs. electrical impulses are guided by chemicals, not electrical signals.

This is a pretty explicit choice to make, so we'll have to find a reason in the passage to make it.

What is the "evidence" all these answer choices are referring to?

The word appears in line 29. If we trace backwards, this evidence is intended to support "this theory" in line 20. What is "this theory"? That goes back to "this alternative theory" in line 11.

What is "this alternative theory"?

Line 7-11, neurobiologists speculating that electrical impulses are transmitted chemically rather than electrically.

So the evidence referred to in all the answer choices is meant to show that electrical impulse transmission is chemical, not electrical.

Although, the 1st sentence of the psg. says that neurobiologists once believed that the workings of the brain were exclusively electrical, that only allows us to infer that nowadays they believe the workings of the brain are not EXCLUSIVELY electrical.

Nothing in the passage says that "the workings of the brain" are chemical not electrical. That would change everything about how the brain operates, while this passage is really just about how neurons leap across synapses.

== other answers ===
(B) has the same 1st half as (A), which is incorrect. And (B) has the same 2nd half as (C), which is more narrow and less important than the 2nd half of (A)/(D)/(E).

(E) has a 1st half that does not emphasize the correct main point. The difference in receptor molecules leads into the final paragraph's point, but (E) misses the whole conceptual shift of the OLD idea (electrical signals leap across synapses) to the NEW idea (chemicals control the receptivity of neurons to electrical transmission).