Scientists studying the activity of the
living brain with widely used new imaging techniques have been missing some of
the earliest steps in brain activity because those changes are subtle and are
masked by reactions that happen seconds later, Israeli scientists say.
The imaging techniques — positron emission tomography scanning and
magnetic resonance imaging, known as PET and functional M. R. I. scans — are
used prominently in studies of brain activity. The most active brain areas
appear to light up on the scans as specific tasks are performed. The two
techniques do not measure nerve-cell activity directly; they measure the extra
flow of blood that surges to the most active brain areas.
Researchers at the Weizmann Institute of Science in Rehovot, Israel, have
monitored these changes in blood flow in anesthetized cats by removing parts of
the
A. Because there is early oxygen transfer.
B. Because they do not form their images quickly enough to follow such rapid changes.
C. Because researchers control the changes in blood flow.
D. Because early oxygen transfer gives the flow blood energy.
更多"Scientists studying the activity of"的相关试题:
[单项选择]
Scientists studying the activity of the
living brain with widely used new imaging techniques have been missing some of
the earliest steps in brain activity because those changes are subtle and are
masked by reactions that happen seconds later, Israeli scientists say.
The imaging techniques — positron emission tomography scanning and
magnetic resonance imaging, known as PET and functional M. R. I. scans — are
used prominently in studies of brain activity. The most active brain areas
appear to light up on the scans as specific tasks are performed. The two
techniques do not measure nerve-cell activity directly; they measure the extra
flow of blood that surges to the most active brain areas.
Researchers at the Weizmann Institute of Science in Rehovot, Israel, have
monitored these changes in blood flow in anesthetized cats by removing parts of
the
A. those changes are subtle and masked by some reactions
B. subtle changes in blood flow began earlier
C. the imaging techniques are out of place
D. the flow of blood to increase to an area of the brain is slow
[单项选择] Scientists studying the effect of large volcanic eruptions on global climate have long focused on the major quantities of carbon dioxide (C02), a gas known to contribute to the greenhouse effect, produced by these eruptions. It is well observed that such greenhouse gases trap heat radiated from the surface of the earth, thereby forming a type of insulation around the planet. The greenhouse effect is essential for ecological equipoise because it maintains the temperature of the planet within habitable parameters, but there is growing concern that man-made production of gases such as CO[,2] from the burning of fossil fuels may be threatening the system’’s tolerance, and have resulted in excessive warming on a global scale. While volcanic eruptions indubitably metabolize and accumulate C0[,2] in the atmosphere, it has been recently discovered that their impact is virtually trivial compared to the quantity produced by human activities, especially heavy industry. In reality, the more subs
A. The deep and enduring effect that volcanic eruptions have on the environment
B. The process by which classic volcanic eruptions tend to occur
C. The relative dearth of cases with scientists can judge the effects of volcain eruptions
D. A sample case with which later volcanic explosions are compared
E. The global cooling effects of one of the best-studied volcanic eruptions
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