Read the passage about prebiotics, rats and sleep carefully and answer the question: Prebiotics are the lesser-known gut-health promoters which serve as food for good bacteria inside the gut. "We found that dietary prebiotics can improve non-REM (random eye movement) sleep, as well as REM sleep after a stressful event," said Robert Thompson, a PhD researcher at University of Colorado Boulder in the U.S. Prebiotics are dietary fibres found naturally in foods like artichokes, raw garlic, leeks and onions. When beneficial bacteria digest prebiotic fibre, they not only multiply, improving overall gut health, but they also release metabolic by-products. Researchers fed three-week-old male rats a diet of either standard chow or chow that included prebiotics. They then monitored the rats body temperature, gut bacteria and sleep-wake cycles using electroencephalogram (EEG), or brain activity testing over time. Findings revealed that the rats on the prebiotic diet spent more time in non-rapid-eye-movement (NREM) sleep, which is restful and restorative, than those on the non-prebiotic diet. How can sleep-wake cycles be monitored in this study?

Introduction / Context:
This comprehension question focuses on understanding the research method described in the passage. The scientists did not simply observe the rats visually but used a specific technical tool to monitor sleep-wake cycles and brain activity over time. The candidate must recall which instrument is mentioned and how it is used in the context of the study.

Given Data / Assumptions:
- The passage states that the researchers monitored body temperature, gut bacteria, and sleep-wake cycles. - It explains that they did this “using electroencephalogram (EEG), or brain activity testing over time”. - NREM and REM sleep are types of sleep described, but they are outcomes rather than tools. - The question asks specifically “How can sleep-wake cycles be monitored in this study?”

Concept / Approach:
The correct approach is to identify the explicit mention of a scientific instrument used for measuring sleep. An electroencephalogram (EEG) records electrical activity of the brain and is a standard tool in sleep research. The passage clearly links EEG to monitoring sleep-wake cycles. Options that describe general conditions or other measures such as body temperature do not directly answer the “how” of monitoring the cycles.

Step-by-Step Solution:
Step 1: Revisit the part of the passage that describes the researchers actions after feeding the rats. Step 2: Note the sentence: “They then monitored the rats body temperature, gut bacteria and sleep-wake cycles using electroencephalogram (EEG), or brain activity testing over time.” Step 3: Identify that EEG is explicitly mentioned as the method used to monitor sleep-wake cycles. Step 4: Recognise that the phrase “brain activity testing over time” further clarifies the function of EEG in the experiment. Step 5: Match this with option C, “By using EEG”. Step 6: Confirm that other options either misinterpret or do not fully capture the monitoring method.

Verification / Alternative check:
Option A, “By testing brain power”, is vague and does not refer to a specific instrument. Option B, “By allowing REM and NREM sleep”, describes what happens to the rats but not how researchers measure it. Option D, “By recording body temperature”, captures only one parameter and is not identified as the main measure of sleep-wake cycles. Option E, “By checking only eye movements”, is incomplete and not supported by the passage. Therefore, only option C correctly represents the method described.

Why Other Options Are Wrong:
Testing brain power: The passage mentions brain activity testing with EEG, but “brain power” is an imprecise term and not the method used. Allowing REM and NREM sleep: This describes the occurrence of sleep stages, not the monitoring technique. Recording body temperature: This is one of the research measurements but does not directly equate to tracking sleep-wake cycles. Checking only eye movements: The text does not say that eye movements alone were used as an index; it emphasises EEG instead.

Common Pitfalls:
Students sometimes overlook technical terms in a passage or feel intimidated by them. As a result, they may skip over “electroencephalogram (EEG)” and choose a more familiar-sounding but incorrect option. In scientific reading passages, it is important to pay attention to such terms, because exam questions often focus exactly on these details. Underline or mentally note any specialised instrument names when reading.

Final Answer:
In this study, sleep-wake cycles are monitored by using EEG, that is, electroencephalogram recordings of brain activity over time.