2005年上海交大考博英语真题

2014-01-17 18:46:29来源：新东方在线整理

passage 3

You can have toomuch of a good thing,it seems---at least when it comes to physiotherapy after astroke. Many doctors believe that it is the key to recovery:exetcising apartially paralyzed limb can help the brain “rewire”itself and replace neuralconnections destroyed by a clot in the brain.

But the latest animalexperiments suggest that too much exercise too soon after a brain injury canmake the damage worse. “It’s something that clinicians are not aware of,”saysTimothy Schallert of the University at Austin,wholed the research.

In some trials,stroke victims asked to puttheir good arm in a sling---to force them to use their partially paralyzedlimb---had made much better recoveries than those who used their good arm. Butthese patients were treated many months after their strokes.Earlier intervention,Schallertreasoned,should lead to even more dramatic improvements.

To test this theory,Schallert and hiscolleagues placed tiny casts on the good forelimbs of rats for two weeksimmediately after they were given a small brain injury that partially paralyzedone forelimb.Several weeks later, the researchers were astonished to find thatbrain tissue surruouding the original injury had also died. “The size of theinjury doubled. It’s very dramatic effect.”says Schallert.

Brain-injured rats that were not forced tooveruse their partially paralyzed limbs showed no similar damage,and the castsdid not cause a dramatic loss of brain tissue in animals that had not alreadysuffered minor brain damage.In subsequent experiments,the researchers havefound that the critical period for exercise-induced damage in rats is the firstweek after the initial brain injury.

The spreading brain damage witnessed bySchaller’s team was probably caused by the release of glutamate,aneurotransmitter,from brain cells stimulated during limb movement.At high doses,glutamateis toxic even to healthy nerve cells.And Schallert believes that a brain injurymakes neighboring cells unusually susceptible to the neurotransmitter’s toxiceffects.

RandolphNudo of the University of Texas Health Science Center at Houston,who studiesbrain injury in primates,agrees that glutamate is the most likely culprit.Inexperiments with squirrel monkeys suffering from stroke-like damage,Nudo triedbeginning rehabilitation within five days of injury.Although the treatment wasbebeficial in the long run,Nudo noticed an initial worsening of the paralysisthat might also have been due to brain damage brought on by exercise.

Schallert stresses that mild exercise islikely to be beneficial however soon it begins.He adds that it is unclearwhether human victims of strokes,like brain -injured rats,could make theirproblems worse by exercising too vigorously,too soon.

Some clinics do encourage patients to beginphysiotherapy within a few weeks of suffering a traumatic head injury orstroke,says David Hovda,director of brain injury research at the University ofCalifornia,Los Angeles.But even if humans do have a similar period ofvulnerability to rat,he speculates that it might be possible to use drugs toblock the effects of glutamate.

71. Schallert issued a warning tothose who____

A.believe in the possibility of rewiring thebrain

B.are ignorant of physiotherapy in the clinic

C.add exercise to partially paralyzed limbs

D.are on the verge of a stroke

72.Which of the following isSchallert’s hypothesis for his investigation.?

A.Earlier intervention should lead to evenmore dramatic improvements.

B.The critical period for braim damage is oneweek after injury.

C.A partially paralyzed limb can cause braindamages

D.Physiotherapy is the key to brain recovery.

73.The results from Schallert’s research____

A.reinforcedthe singificance of physiotherapy after a stroke