MCAT Behavioral Sciences Question 193: Answer and Explanation

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Question: 193

5.

Figure 1 Average Melatonin Production (in ng/mL) over a 24-hour Period by Age Group

A normal 15 year old is participating in a sleep study and falls asleep at 10:30. This subject enters her first REM cycle at midnight. According to Figure 1 above, which of the following measures would most likely be recorded at midnight?

I. Melatonin levels of 90 ng/mL

II. Moderate to high EMG activity

III. EEG measures include theta waves and K-complexes

  • A. I only
  • B. III only
  • C. I and III only
  • D. I, II, and III

Correct Answer: A

Explanation:

Item I is true: according to Figure 1, 90 ng/mL of melatonin would be within the normal range for a 15 year old at approximately midnight (choice B can be eliminated). Item II is false: during REM sleep, the brain stem inhibits movement, therefore EMG activity is very low or absent (choice D can be eliminated). Item III is false: theta waves and K-complexes are present during stage 2 sleep, but absent during REM sleep (choice C can be eliminated and choice A is correct).

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