Motherhood may make women smarter and may help prevent dementia(痴呆) in old age by bathing

Motherhood may make women smarter and may help prevent dementia(痴呆) in old age by bathing the brain in protective hormones(荷尔蒙) , U.S. reseachers reported on Thursday.
Tests on rats show that those who raise two or more litters of pups do considerably better in tests of memory and skills than rats who have no babies, and their brains show changes that suggest they may be protected against diseases such as Alzheimer’s(老年痴呆症). University of Richmond psychology professor Craig Kinsley believes his findings will translate into humans.
“Our research shows that the hormones of pregnancy are protecting the brain, including estrogen(雌激素), which we know has many neuroprotective (保护神经的) effects,” Kinsley said.  
“It’s rat data but humans are mammals just like these animals are mammals,” he added in a telephone interview. “They go through pregnancy and hormonal changes.”
Kinsley said he hoped public health officials and researchers will look to see if having had children protects a woman from Alzheimer’s and other forms of age-related brain decline.
“When people think about pregnancy, they think about what happens to babies and the mother from the neck down,” said Kinsley, who presented his findings to the annual meeting of the Society of Neuroscience in Orlando, Florida.
“They do not realize that hormones are washing on the brain. If you look at female animals who have never gone through pregnancy, they act differently toward young. But if she goes through pregnancy, she will sacrifice her life for her infant—that is a great change in her behavior that showed in genetic alterations(改变) to the brain.”
【小题1】What can protect the brain of a woman according to the passage?( within 4 words)
【小题2】 How do scientists know “Motherhood may make women smarter”?( within 8 words)
【小题3】“It’s rat data but humans are mammals just like these animals are mammals.” What does the sentence suggest?  ( within 13 words)
【小题4】What’s the main idea of this passage? (within 10 words)The hormones of pregnancy.