Passage
At the blood-brain barrier, the cerebral spinal fluid (CSF) is separated from lymphatic circulation by epithelial cells bound by tight junctions. Within the central nervous system (CNS) , CSF surrounds and protects the brain and spinal cord and is believed to function in waste clearance for the CNS analogous to the role of the lymphatic system within the body.This waste clearance system has been dubbed the "glymphatic system." Although the mechanism of clearance is largely unknown, specialized glial cells known as astrocytes appear to modify the interstitial volume between neurons. This increase in interstitial volume allows for greater CSF flow, which increases the efficiency of neurotoxic clearance. Waste products removed from the brain include metabolic products such as ammonia and harmful compounds such as amyloid proteins.Recent advances in imaging technology suggest that interstitial clearance may be modified during sleep. To test this hypothesis, researchers indirectly studied changes in interstitial volume by measuring the percentage of CSF coverage in animal models during the first hour of sleep and again during the first hour of wakefulness (Figure 1) .
Figure 1. Percentage of CSF coverage of interstitial space during sleep and wakefulness
-A second study is performed to measure CSF coverage against brain wave frequency, measured by electroencephalography. Which of the following findings would best support the data provided in the passage?

Question

Passage
At the blood-brain barrier, the cerebral spinal fluid (CSF) is separated from lymphatic circulation by epithelial cells bound by tight junctions. Within the central nervous system (CNS) , CSF surrounds and protects the brain and spinal cord and is believed to function in waste clearance for the CNS analogous to the role of the lymphatic system within the body.This waste clearance system has been dubbed the "glymphatic system." Although the mechanism of clearance is largely unknown, specialized glial cells known as astrocytes appear to modify the interstitial volume between neurons. This increase in interstitial volume allows for greater CSF flow, which increases the efficiency of neurotoxic clearance. Waste products removed from the brain include metabolic products such as ammonia and harmful compounds such as amyloid proteins.Recent advances in imaging technology suggest that interstitial clearance may be modified during sleep. To test this hypothesis, researchers indirectly studied changes in interstitial volume by measuring the percentage of CSF coverage in animal models during the first hour of sleep and again during the first hour of wakefulness (Figure 1) .

Figure 1. Percentage of CSF coverage of interstitial space during sleep and wakefulness
-A second study is performed to measure CSF coverage against brain wave frequency, measured by electroencephalography. Which of the following findings would best support the data provided in the passage?

Quizplus · Accepted Answer

11ecba2d_0f38_5fb4_a3bf_fd692e30fa5f_MD0008_00 The data in Figure 1 suggest that CSF coverage is greater during sleep than during wakefulness, at least within the first 60 minutes. Because the first few stages of sleep involve a progression from higher to lower frequency brainwaves, these findings are best supported by the graph showing that CSF coverage increases as brain wave frequency decreases within the first hour of sleep. Educational objective: Brain frequencies observed during most sleep stages are lower than brain frequencies observed during wakefulness.

Passage At the Blood-Brain Barrier, the Cerebral Spinal Fluid (CSF) Is