(2019·桂林联考)By trying to tickle(使发痒) rats and recording how their nerve cells respond，Shimpei Ishiyama and his adviser are discovering a mystery that has puzzled thinkers since Aristotle expected that humans，given their thin skin and unique ability to laugh，were the only ticklish animals.
It turns out that Aristotle was wrong.In their study published on Thursday，Ishiyama and his adviser Michael Brecht found that rats squeaked and jumped with pleasure when tickled on their backs and bellies.These signs of joy changed according to their moods.And for the first time，they discovered a special group of nerve cells.These nerve cells made this feeling so powerful that it causes a rat being tickled to lose control.
To make sure that he had indeed found a place in the brain where tickling was processed，Ishiyama then stimulated(刺激) that area with electrical currents.The rats began to jump like rabbits and sing like birds.
“It's truly ground－breaking，”said Jeffrey Burgdorf，a neuroscientist at Northwestern University who reviewed the paper.“It takes the study of emotion to a new level.”
Burgdorf has played a central role in our understanding of animal tickling.He was part of a team that first noticed，in the late 1990s，that rats made special noises when they were experiencing social pleasure.Others had already noted that rats repeatedly made short and high sounds during meals.But the lab where Burgdorf worked noticed that they emitted similar sounds while playing.And so one day，the senior scientist in the lab said，“Let's go and tickle some rats.” They quickly found that those cries of pleasure doubled.
“The authors have been very adventurous，” said Daniel O'Connor，a neuroscientist at Johns Hopkins University.To him，that finding was very surprising.
“Why does the world literally feel different when you are stressed out？” he said.“This is the first step towards answering that question.It gives us a way to approach it with experimental rigor(严谨)．”
【语篇解读】 本文是一篇说明文。文章中科学家通过刺激老鼠来记录它们的神经细胞的反应，所得出的结论将对情绪的研究提升到了一个新的高度。
1．What contributed to humans' being ticklish according to Aristotle?
A．Their special skin.
B．Their social pleasure.
C．Their nervous system.
D．Their willingness to touch.
A [细节理解题。根据文章第一段中的“since Aristotle expected that humans，given their thin skin and unique ability to laugh，were the only ticklish animals”可知，亚里士多德认为人类由于其皮肤薄，而且有独特的笑的能力而成为唯一怕痒的动物，所以正确答案为A。]
2．Which of the following statements will Jeffrey Burgdorf agree with?
A．The research process is full of risks.
B．The finding of the study is surprising and unbelievable.
C．The new discovery is beneficial for the study of emotion.
D．The finding of the study actually contradicts modern science.
C [推理判断题。根据文章第四段中的“It takes the study of emotion to a new level”可知，这项研究成果把对情绪的研究提升到了一个新的高度，显然，这对情绪的研究是有益处的。故答案为C。]
3．The underlined word “squeaked” in Paragraph 2 may be replaced by “ ．”
A．gave a smile
B．made a noise
C．burst into tears
D．watched with staring eyes
B [词义猜测题。根据该词后面的“jumped with pleasure when tickled on their backs and bellies”可知，当在老鼠的背部和腹部挠痒痒的时候，它们会高兴地跳起来，再结合第三段中的“The rats began to jump like rabbits and sing like birds”可知，此处是“发出声音”的意思，故选B。]
4．What is the best title for the text?
A．The Life of Rats
B．How Rats Laugh
C．A Wonderful Scientist
D．A New Discovery about Rats
D [标题归纳题。根据全文内容可知，文章主要讲述了一项关于老鼠的新发现。故答案为D。]
