French paediatric neurosurgeon Georg Dorfmuller (61-year-old) poses in a room at the post COVID-19 unit of the Le Parc Hospital in Taverny near Paris during the outbreak of the coronavirus disease (COVID-19) in France, April 30, 2020. REUTERS/Benoit Tessier

French paediatric neurosurgeon Georg Dorfmuller (61-year-old) practices re-education exercises with physiotherapist Laura Ciocanas at the post COVID-19 unit of the Le Parc Hospital in Taverny near Paris during the outbreak of the coronavirus disease (COVID-19) in France, April 30, 2020. REUTERS/Benoit Tessier

French paediatric neurosurgeon Georg Dorfmuller (61-year-old) practices re-education exercises with physiotherapist Laura Ciocanas at the post COVID-19 unit of the Le Parc Hospital in Taverny near Paris during the outbreak of the coronavirus disease (COVID-19) in France, April 30, 2020. REUTERS/Benoit Tessier

French paediatric neurosurgeon Georg Dorfmuller (61-year-old) poses in a room at the post COVID-19 unit of the Le Parc Hospital in Taverny near Paris during the outbreak of the coronavirus disease (COVID-19) in France, April 30, 2020. REUTERS/Benoit Tessier

French paediatric neurosurgeon Georg Dorfmuller (61-year-old) practices re-education exercises with physiotherapist Laura Ciocanas at the post COVID-19 unit of the Le Parc Hospital in Taverny near Paris during the outbreak of the coronavirus disease (COVID-19) in France, April 30, 2020. REUTERS/Benoit Tessier

French paediatric neurosurgeon Georg Dorfmuller (61-year-old) poses in a room at the post COVID-19 unit of the Le Parc Hospital in Taverny near Paris during the outbreak of the coronavirus disease (COVID-19) in France, April 30, 2020. REUTERS/Benoit Tessier

Alim Louis Benabid, a neurosurgeon and professor at the University of Grenoble, shows one of two recording devices containing 64 electrodes which collected brain signals to be implanted one either side of the patient's head during a news conference after Thibault, a 28-year-old man, paralyzed from the shoulders down, had been able to walk using a robotic exoskeleton controlled by his own mind, at the French research center Clinatec in Grenoble, France, October 7, 2019. REUTERS/Emmanuel Foudrot

Alim Louis Benabid, a neurosurgeon and professor at the University of Grenoble, attends a news conference after Thibault, a 28-year-old man, paralyzed from the shoulders down, had been able to walk using a robotic exoskeleton controlled by his own mind, at the French research center Clinatec in Grenoble, France, October 7, 2019. REUTERS/Emmanuel Foudrot

Alim Louis Benabid, a neurosurgeon and professor at the University of Grenoble, attends a news conference after Thibault, a 28-year-old man, paralyzed from the shoulders down, had been able to walk using a robotic exoskeleton controlled by his own mind, at the French research center Clinatec in Grenoble, France, October 7, 2019. REUTERS/Emmanuel Foudrot

Alim Louis Benabid, a neurosurgeon and professor at the University of Grenoble, attends a news conference after Thibault, a 28-year-old man, paralyzed from the shoulders down, had been able to walk using a robotic exoskeleton controlled by his own mind, at the French research center Clinatec in Grenoble, France, October 7, 2019. REUTERS/Emmanuel Foudrot

Oscar Antonio Navarrete, 18, a student, who was injured during a protest against Venezuela's President Nicolas Maduro's government, lies in a hospital bed, in Caracas, Venezuela, August 17, 2017. Relatives of Navarrete said he was hit in the chest by a tear gas canister on May 18, 2017. He lost consciousness and his heart stopped for several minutes. He cannot walk, suffers short-term memory loss, severe motor sequelae and has cerebral edema - an accumulation of fluid in the brain. Today, he lives in a hospital and needs rehabilitation and treatment by specialist doctors including neurosurgeons, speech therapists and psychologists. Oscar's mother says her son was angry about crisis in the country, and protested because it affected everyone. "It was worth it, because none of this will be forgotten. The world needs to see all this, I have faith that things will change," said Navarrete's mother Elizabeth. REUTERS/Ueslei Marcelino SEARCH "VENEZUELA INJURIES" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES.

U.S. President Donald Trump and Ben Carson (C), his nominee to lead the Department of Housing and Urban Development (HUD), joined by Carson's wife, Candy Carson, look at the exhibit dedicated to Carson's distinguished career as a neurosurgeon during a visit to the National Museum of African American History and Culture on the National Mall in Washington, U.S., February 21, 2017. REUTERS/Jonathan Ernst

U.S. President Donald Trump and Ben Carson (C), his nominee to lead the Department of Housing and Urban Development (HUD), look at the exhibit dedicated to Carson's distinguished career as a neurosurgeon during a visit to the National Museum of African American History and Culture on the National Mall in Washington, U.S., February 21, 2017. REUTERS/Jonathan Ernst

U.S. President Donald Trump (R) and Ben Carson (2nd R), his nominee to lead the Department of Housing and Urban Development (HUD), look at the exhibit dedicated to Carson's distinguished career as a neurosurgeon during a visit to the National Museum of African American History and Culture on the National Mall in Washington, U.S., February 21, 2017. REUTERS/Jonathan Ernst

Italian neurosurgeon Dr. Sergio Canavero who hopes to perform the world's first human head transplant speaks to media ahead of a medical conference in Glasgow , Scotland, Britain November 18 2016. REUTERS/Russell Cheyne

Italian neurosurgeon Dr. Sergio Canavero who hopes to perform the world's first human head transplant speaks to media ahead of a medical conference in Glasgow , Scotland, Britain November 18 2016. REUTERS/Russell Cheyne

Italian neurosurgeon Dr. Sergio Canavero who hopes to perform the world's first human head transplant speaks to media ahead of a medical conference in Glasgow , Scotland, Britain November 18 2016. REUTERS/Russell Cheyne

Italian neurosurgeon Dr. Sergio Canavero who hopes to perform the world's first human head transplant speaks to media ahead of a medical conference in Glasgow , Scotland, Britain November 18 2016. REUTERS/Russell Cheyne

Italian neurosurgeon Dr. Sergio Canavero who hopes to perform the world's first human head transplant speaks to media ahead of a medical conference in Glasgow , Scotland, Britain November 18 2016. REUTERS/Russell Cheyne

Italian neurosurgeon Dr. Sergio Canavero, who hopes to perform the world's first human head transplant, speaks to media ahead of a medical conference in Glasgow, Scotland, Britain November 18 2016. REUTERS/Russell Cheyne

Italian neurosurgeon Dr. Sergio Canavero, who hopes to perform the world's first human head transplant, speaks to media ahead of a medical conference in Glasgow, Scotland, Britain November 18 2016. REUTERS/Russell Cheyne

Neurosurgeon Linda Liau, MD, 49, Professor and Director of the UCLA Brain Tumor Program (C) removes a brain tumour from a patient at the Ronald Reagan UCLA Medical Center in Los Angeles, California, United States, May 26, 2016. Liau has been a neurosurgeon for 25 years and has developed a brain cancer vaccine that is in clinical trials. “It’s a very male-dominated profession... When you walk into the room they assume you’re the nurse or the assistant as opposed to the actual surgeon," Liau said. "I think ultimately the goal would be to be gender-blind completely, so the fact that we’re even talking about having a female president as a novelty is in a way sad." Picture taken May 26, 2016. REUTERS/Lucy Nicholson SEARCH "WOMEN WORKERS" FOR THIS STORY. SEARCH "THE WIDER IMAGE" FOR ALL STORIES

Neurosurgeon Linda Liau, MD, 49, Professor and Director of the UCLA Brain Tumor Program walks out of the operating theatre after successfully removing a tumour from a patient at the Ronald Reagan UCLA Medical Center in Los Angeles, California, United States, May 26, 2016. Liau has been a neurosurgeon for 25 years and has developed a brain cancer vaccine that is in clinical trials. ÒItÕs a very male-dominated profession... When you walk into the room they assume youÕre the nurse or the assistant as opposed to the actual surgeon," Liau said. "I think ultimately the goal would be to be gender-blind completely, so the fact that weÕre even talking about having a female president as a novelty is in a way sad." Picture taken May 26, 2016. REUTERS/Lucy Nicholson SEARCH "WOMEN WORKERS" FOR THIS STORY. SEARCH "THE WIDER IMAGE" FOR ALL STORIES

Ben Carson, retired American neurosurgeon and former candidate for President of the United States, speaks at the Republican National Convention in Cleveland, Ohio, U.S. July 19, 2016. REUTERS/Aaron Josefczyk

Ben Carson, retired American neurosurgeon and former candidate for President of the United States, speaks at the Republican National Convention in Cleveland, Ohio, U.S. July 19, 2016. REUTERS/Mark Kauzlarich

Ben Carson, retired American neurosurgeon and former candidate for President of the United States, speaks at the Republican National Convention in Cleveland, Ohio, U.S. July 19, 2016. REUTERS/Aaron P. Bernstein

A traffic sign for Baltimore is seen on a highway near Baltimore, Maryland November 5, 2015. For many who knew Ben Carson in Baltimore, his U.S. presidential candidacy comes as a surprise. Over more than three decades as a Baltimore resident ending in 2013, Carson - now a front-runner in the race for the Republican Party nomination - rarely spoke about his political views. An unassailable local hero, a Johns Hopkins Hospital neurosurgeon, Carson put his wealth to use helping the poor. He established a scholarship program for school children and hosted a banquet each year to honor its recipients. Picture taken November 5, 2015. REUTERS/Carlos Barria

A man crosses a street in front of the John Hopkins Hospital in Baltimore, Maryland November 4, 2015. For many who knew Ben Carson in Baltimore, his U.S. presidential candidacy comes as a surprise. Over more than three decades as a Baltimore resident ending in 2013, Carson - now a front-runner in the race for the Republican Party nomination - rarely spoke about his political views. An unassailable local hero, a Johns Hopkins Hospital neurosurgeon, Carson put his wealth to use helping the poor. He established a scholarship program for school children and hosted a banquet each year to honor its recipients. Picture taken November 4, 2015. REUTERS/Carlos Barria

A popeyes restaurant sign is seen on the intersections of Broadway and New Orleans a cross the street from the John Hopkins Hospital in Baltimore, Maryland November 4, 2015. For many who knew Ben Carson in Baltimore, his U.S. presidential candidacy comes as a surprise. Over more than three decades as a Baltimore resident ending in 2013, Carson - now a front-runner in the race for the Republican Party nomination - rarely spoke about his political views. An unassailable local hero, a Johns Hopkins Hospital neurosurgeon, Carson put his wealth to use helping the poor. He established a scholarship program for school children and hosted a banquet each year to honor its recipients. Picture taken November 4, 2015. REUTERS/Carlos Barria

The John Hopkins Hospital is seen at a area near the downtown of Baltimore, Maryland November 4, 2015. For many who knew Ben Carson in Baltimore, his U.S. presidential candidacy comes as a surprise. Over more than three decades as a Baltimore resident ending in 2013, Carson - now a front-runner in the race for the Republican Party nomination - rarely spoke about his political views. An unassailable local hero, a Johns Hopkins Hospital neurosurgeon, Carson put his wealth to use helping the poor. He established a scholarship program for school children and hosted a banquet each year to honor its recipients. Picture taken November 4, 2015. REUTERS/Carlos Barria

A holy Bible Book is seen at the Spencerville Seventh Day Adventist Church in Silver Spring, Maryland November 4, 2015. For many who knew Ben Carson in Baltimore, his U.S. presidential candidacy comes as a surprise. Over more than three decades as a Baltimore resident ending in 2013, Carson - now a front-runner in the race for the Republican Party nomination - rarely spoke about his political views. An unassailable local hero, a Johns Hopkins Hospital neurosurgeon, Carson put his wealth to use helping the poor. He established a scholarship program for school children and hosted a banquet each year to honor its recipients. Picture taken November 4, 2015. REUTERS/Carlos Barria

A man walks by a popeyes restaurant a cross the street from the John Hopkins Hospital in Baltimore, Maryland November 4, 2015. For many who knew Ben Carson in Baltimore, his U.S. presidential candidacy comes as a surprise. Over more than three decades as a Baltimore resident ending in 2013, Carson - now a front-runner in the race for the Republican Party nomination - rarely spoke about his political views. An unassailable local hero, a Johns Hopkins Hospital neurosurgeon, Carson put his wealth to use helping the poor. He established a scholarship program for school children and hosted a banquet each year to honor its recipients. Picture taken November 4, 2015. REUTERS/Carlos Barria

The John Hopkins Hospital is seen at a area near the downtown of Baltimore, Maryland November 4, 2015. For many who knew Ben Carson in Baltimore, his U.S. presidential candidacy comes as a surprise. Over more than three decades as a Baltimore resident ending in 2013, Carson - now a front-runner in the race for the Republican Party nomination - rarely spoke about his political views. An unassailable local hero, a Johns Hopkins Hospital neurosurgeon, Carson put his wealth to use helping the poor. He established a scholarship program for school children and hosted a banquet each year to honor its recipients. Picture taken November 4, 2015. REUTERS/Carlos Barria

A man walks by the John Hopkins Hospital in Baltimore, Maryland November 4, 2015. For many who knew Ben Carson in Baltimore, his U.S. presidential candidacy comes as a surprise. Over more than three decades as a Baltimore resident ending in 2013, Carson - now a front-runner in the race for the Republican Party nomination - rarely spoke about his political views. An unassailable local hero, a Johns Hopkins Hospital neurosurgeon, Carson put his wealth to use helping the poor. He established a scholarship program for school children and hosted a banquet each year to honor its recipients. Picture taken November 4, 2015. REUTERS/Carlos Barria

A countryside road is seen during a hazy day in Upperco Maryland November 5, 2015. For many who knew Ben Carson in Baltimore, his U.S. presidential candidacy comes as a surprise. Over more than three decades as a Baltimore resident ending in 2013, Carson - now a front-runner in the race for the Republican Party nomination - rarely spoke about his political views. An unassailable local hero, a Johns Hopkins Hospital neurosurgeon, Carson put his wealth to use helping the poor. He established a scholarship program for school children and hosted a banquet each year to honor its recipients. Picture taken November 5, 2015. REUTERS/Carlos Barria

The Spencerville Seventh Day Adventist Church is seen in Silver Spring, Maryland November 4, 2015. For many who knew Ben Carson in Baltimore, his U.S. presidential candidacy comes as a surprise. Over more than three decades as a Baltimore resident ending in 2013, Carson - now a front-runner in the race for the Republican Party nomination - rarely spoke about his political views. An unassailable local hero, a Johns Hopkins Hospital neurosurgeon, Carson put his wealth to use helping the poor. He established a scholarship program for school children and hosted a banquet each year to honor its recipients. Picture taken November 4, 2015. REUTERS/Carlos Barria

Cars are seen waiting on traffic as they enter Baltimore, Maryland November 5, 2015. For many who knew Ben Carson in Baltimore, his U.S. presidential candidacy comes as a surprise. Over more than three decades as a Baltimore resident ending in 2013, Carson - now a front-runner in the race for the Republican Party nomination - rarely spoke about his political views. An unassailable local hero, a Johns Hopkins Hospital neurosurgeon, Carson put his wealth to use helping the poor. He established a scholarship program for school children and hosted a banquet each year to honor its recipients. Picture taken November 5, 2015. REUTERS/Carlos Barria

An abandon building is seen near the John Hopkins Hospital in Baltimore, Maryland November 5, 2015. For many who knew Ben Carson in Baltimore, his U.S. presidential candidacy comes as a surprise. Over more than three decades as a Baltimore resident ending in 2013, Carson - now a front-runner in the race for the Republican Party nomination - rarely spoke about his political views. An unassailable local hero, a Johns Hopkins Hospital neurosurgeon, Carson put his wealth to use helping the poor. He established a scholarship program for school children and hosted a banquet each year to honor its recipients. Picture taken November 5, 2015. REUTERS/Carlos Barria

A sign which reads "Run Ben Run" is support of presidential candidate Ben Carson is seen next to a countryside road in Upperco Maryland November 5, 2015. For many who knew Ben Carson in Baltimore, his U.S. presidential candidacy comes as a surprise. Over more than three decades as a Baltimore resident ending in 2013, Carson - now a front-runner in the race for the Republican Party nomination - rarely spoke about his political views. An unassailable local hero, a Johns Hopkins Hospital neurosurgeon, Carson put his wealth to use helping the poor. He established a scholarship program for school children and hosted a banquet each year to honor its recipients. Picture taken November 5, 2015. REUTERS/Carlos Barria

An man sits on a bench near the John Hopkins Hospital in Baltimore, Maryland November 5, 2015. For many who knew Ben Carson in Baltimore, his U.S. presidential candidacy comes as a surprise. Over more than three decades as a Baltimore resident ending in 2013, Carson - now a front-runner in the race for the Republican Party nomination - rarely spoke about his political views. An unassailable local hero, a Johns Hopkins Hospital neurosurgeon, Carson put his wealth to use helping the poor. He established a scholarship program for school children and hosted a banquet each year to honor its recipients. Picture taken November 5, 2015. REUTERS/Carlos Barria

A campaign sign for U.S. Republican presidential candidate and retired Johns Hopkins neurosurgeon Ben Carson is displayed outside the Iowa State Fair in Des Moines, Iowa August 15, 2015. REUTERS/Joshua Lott

Books titled "Rx For America", about retired neurosurgeon Ben Carson, are seen on a table at the Western Conservative Summit in Denver, Colorado June 27, 2015. REUTERS/Mark Leffingwell

Valery Spiridonov, a man who has volunteered to be the first person to undergo a head transplant, attends a news conference in Vladimir, Russia, June 25, 2015. The 30-year-old Russian, who has a degenerative muscle condition known as Werdnig-Hoffman, wants to become the first person ever to undergo a human head transplant performed by Italian neurosurgeon Dr. Sergio Canavero who says he believes he has a 90 percent chance of success. REUTERS/Maxim Zmeyev

Valery Spiridonov, a man who has volunteered to be the first person to undergo a head transplant, attends a news conference in Vladimir, Russia, June 25, 2015. The 30-year-old Russian, who has a degenerative muscle condition known as Werdnig-Hoffman, wants to become the first person ever to undergo a human head transplant performed by Italian neurosurgeon Dr. Sergio Canavero who says he believes he has a 90 percent chance of success. REUTERS/Maxim Zmeyev

Valery Spiridonov (L), a man who has volunteered to be the first person to undergo a head transplant, attends a news conference in Vladimir, Russia, June 25, 2015. The 30-year-old Russian, who has a degenerative muscle condition known as Werdnig-Hoffman, wants to become the first person ever to undergo a human head transplant performed by Italian neurosurgeon Dr. Sergio Canavero who says he believes he has a 90 percent chance of success. REUTERS/Maxim Zmeyev

Valery Spiridonov (L), a man who has volunteered to be the first person to undergo a head transplant, smiles after attending a news conference in Vladimir, Russia, June 25, 2015. The 30-year-old Russian, who has a degenerative muscle condition known as Werdnig-Hoffman, wants to become the first person ever to undergo a human head transplant performed by Italian neurosurgeon Dr. Sergio Canavero who says he believes he has a 90 percent chance of success. REUTERS/Maxim Zmeyev

Valery Spiridonov, a man who has volunteered to be the first person to undergo a head transplant, attends a news conference in Vladimir, Russia, June 25, 2015. The 30-year-old Russian, who has a degenerative muscle condition known as Werdnig-Hoffman, wants to become the first person ever to undergo a human head transplant performed by Italian neurosurgeon Dr. Sergio Canavero who says he believes he has a 90 percent chance of success. REUTERS/Maxim Zmeyev

Valery Spiridonov, a man who has volunteered to be the first person to undergo a head transplant, is assisted before a news conference in Vladimir, Russia, June 25, 2015. The 30-year-old Russian, who has a degenerative muscle condition known as Werdnig-Hoffman, wants to become the first person ever to undergo a human head transplant performed by Italian neurosurgeon Dr. Sergio Canavero who says he believes he has a 90 percent chance of success. REUTERS/Maxim Zmeyev

Valery Spiridonov (C), a man who has volunteered to be the first person to undergo a head transplant, looks on after a news conference in Vladimir, Russia, June 25, 2015. The 30-year-old Russian, who has a degenerative muscle condition known as Werdnig-Hoffman, wants to become the first person ever to undergo a human head transplant. Italian neurosurgeon Dr. Sergio Canavero is expected to perform the first human head transplant and says he believes he has a 90 percent chance of success. REUTERS/Maxim Zmeyev

Valery Spiridonov, a man who has volunteered to be the first person to undergo a head transplant, attends a news conference in Vladimir, Russia, June 25, 2015. The 30-year-old Russian, who has a degenerative muscle condition known as Werdnig-Hoffman, wants to become the first person ever to undergo a human head transplant performed by Italian neurosurgeon Dr. Sergio Canavero who says he believes he has a 90 percent chance of success. REUTERS/Maxim Zmeyev

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Valery Spiridonov, a man who has volunteered to be the first person to undergo a head transplant, is assisted while being transported during a news conference in Vladimir, Russia, June 25, 2015. The 30-year-old Russian, who has a degenerative muscle condition known as Werdnig-Hoffman, wants to become the first person ever to undergo a human head transplant. Italian neurosurgeon Dr. Sergio Canavero is expected to perform the first human head transplant and says he believes he has a 90 percent chance of success. REUTERS/Maxim Zmeyev

Republican presidential candidate Ben Carson speaks during a Memorial Day rally in Myrtle Beach, South Carolina, May 25, 2015. Carson, a former neurosurgeon, took 25 percent of the vote in a field of 17 candidates at Friday night's Southern Republican Leadership Conference. REUTERS/Randall Hill

Republican presidential candidate Ben Carson speaks during a Memorial Day rally in Myrtle Beach, South Carolina, May 25, 2015. Carson, a former neurosurgeon, took 25 percent of the vote in a field of 17 candidates at Friday night's Southern Republican Leadership Conference. REUTERS/Randall Hill

Republican presidential candidate Ben Carson speaks during a Memorial Day rally in Myrtle Beach, South Carolina, May 25, 2015. Carson, a former neurosurgeon, took 25 percent of the vote in a field of 17 candidates at Friday night's Southern Republican Leadership Conference. REUTERS/Randall Hill

Republican presidential candidate Ben Carson (C) is greeted by supporters during a Memorial Day rally in Myrtle Beach, South Carolina, May 25, 2015. Carson, a former neurosurgeon, took 25 percent of the vote in a field of 17 candidates at Friday night's Southern Republican Leadership Conference. REUTERS/Randall Hill

Political buttons are displayed at a rally for Republican presidential candidate Ben Carson during a Memorial Day rally in Myrtle Beach, South Carolina, May 25, 2015. Carson, a former neurosurgeon, took 25 percent of the vote in a field of 17 candidates at Friday night's Southern Republican Leadership Conference. REUTERS/Randall Hill

Helen Haendle of Murrells Inlet, South Carolin, hands out small American flags during a rally for Republican presidential candidate Ben Carson in Myrtle Beach, South Carolina, May 25, 2015. Carson, a former neurosurgeon, took 25 percent of the vote in a field of 17 candidates at Friday night's Southern Republican Leadership Conference. REUTERS/Randall Hill

Republican presidential candidate Ben Carson (L) talks with a supporter during a Memorial Day rally in Myrtle Beach, South Carolina, May 25, 2015. Carson, a former neurosurgeon, took 25 percent of the vote in a field of 17 candidates at Friday night's Southern Republican Leadership Conference. REUTERS/Randall Hill