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Scientific advances in the latter half of the twentieth century have allowed researchers to study the chemical activities taking place in the human brain during the sleep cycle in more detail. In the 1970s, Jacobs employed these advances to postulate that dreams and hallucinations share a common neurochemical mechanism with respect to the neurotransmitters serotonin and norepinephrine that accounts for the observable similarities between the two states of mind. To test the theory, researchers attempted to elucidate the role of these transmitters in the normal sleep cycle and the effect of hallucinogenic drugs on them.
Serotonin appears important for managing sleep, mood, and appetite, among other functions, while norepinephrine facilitates alertness and mental focus. Both neurotransmitters are discharged in high quantities only during waking states. At the onset of sleep, the neurons that release these neurotransmitters become less active, allowing the brain to enter the three non-rapid eye movement (non-REM) stages of sleep. The non-REM stages typically are not associated with normal dreaming, though parasomnias, such as sleepwalking and confusional arousals, are most common during stage 3. When the brain is ready to enter the fourth stage, REM, which is strongly associated with dreaming, the levels of these two chemicals drop virtually to zero. The Jacobs hypothesis held that the absence of norepinephrine was required to enable the brain to remain asleep, while the absence of serotonin was necessary to allow dreaming to occur
Lysergic acid diethylamide, or LSD, is a semi-synthetic psychedelic drug which causes significant alteration of the senses, memories and awareness; at doses higher than 20 micrograms, it can have a hallucinogenic effect. LSD mimics serotonin well enough to be able to bind at most of the neurotransmitter’s receptor sites, largely inhibiting normal transmission. In addition, the drug causes the locus ceruleus, a cluster of neurons containing norepinephrine, to greatly accelerate activity. If the drug stimulates norepinephrine, thereby precluding sleep, and inhibits serotonin, which Jacobs had postulated was a necessary condition for dreaming, then the resulting hallucinations could merely be “dreaming while awake.” The research thus far is promising but inconclusive; future scientific advances should allow this theory to be tested more rigorously.
1. According to the passage, which of the following is true of the drug lysergic acid diethlyamide?
(A) Research into the drug is promising but inconclusive.
(B) The neuron receptor sites that normally bind serotonin will also bind the drug.
(C) The locus ceruleus causes the drug to affect bodily systems more rapidly than normal.
(D) The drug stimulates norepinephrine and serotonin.
(E) A person who ingests more than 20 micrograms of the drug will have hallucinations.
2. Which of the following best represents the author's primary goal in writing the passage?
(A) to outline a theory and suggest options for further research
(B) to act as an advocate for additional research to help elucidate a particular theory's validity
(C) to introduce a theoretical construct that has not yet been sufficiently proven
(D) to demonstrate the complexities involved in conducting a certain type of scientific research
(E) to articulate a hypothesis and lay out the case for proving it
3. Which of the following, if true, would most undermine the central premise of the Jacobs hypothesis?
(A) LSD does not cause as much long-term neurological damage as previously thought.
(B) Serotonin and norepinephrine rise and fall in tandem.
(C) Researchers prove conclusively that the level of norepinephrine in the brain is a significant factor in enabling the brain to sleep.
(D) Some semi-synthetic hallucinogenic drugs other than LSD do not inhibit serotonin.
(E) The first four stages of sleep are as crucial to the process of dreaming as is the fifth stage.
4. According to the passage, all of the following are true EXCEPT
(A) Norepinephrine and serotonin are discharged only during waking states.
(B) Ingesting more than 20 micrograms of LSD will cause some people to hallucinate.
(C) Rapid eye movement is the stage of sleep during which people dream.
(D) LSD causes neurons to increase the rate at which they discharge norepinephrine.
(E) The absence of serotonin seems to be necessary in order to enable the brain to dream.
5. The passage implies which of the following about the fourth stage of sleep?
(A) One enters the fourth stage of sleep only after passing through the first three stages.
(B) Parasomnias, such as sleepwalking and confusional arousals, don’t occur during the fourth stage of sleep.
(C) “Normal” dreaming occurs more frequently during the fourth stage of sleep than during the first three.
(D) Certain neurotransmitter levels fluctuate rapidly during the fourth stage of sleep.
(E) Serotonin and norepinephrine drop as the result of the brain entering the fourth stage of sleep.
参考答案： BCDAC
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发表于 2021-7-6 07:48:12
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