Power
You can control minds. Sort of.
Brain surgeons can literally control people's ability to use their brains. However, there have been very few new developments in mind control. There's always a lobotomy, but that practice is nearly extinct—for a good reason.
A lobotomy is a medical procedure that consists of the brain surgeon cutting connections from the thalamus to the prefrontal cortex. The point of the surgery was to inhibit a patient's ability to feel emotions. Generally, lobotomies were given to patients with severe mental illnesses.
During the 1940s and 1950s, over 40,000 people received lobotomies—in other words, over 40,000 people had a trusted medical professional basically remove their personality and turn them into a zombie. Yikes.
One Flew Over the Cuckoo's Nest shoved the ethical implications of this medical procedure into the spotlight. It didn't seem like such a good idea anymore once everyone saw that it was basically a removal of the patient's personality. Not everyone has the greatest personality, but it isn't really the surgeon's place to determine whether or not they get to keep it.
The practice declined thanks to new anti-psychotic drugs that are now on the market. Nowadays, neurosurgeons' power is carried out a little more ethically. You'll have the power over life and death, the power to prescribe something that can help a patient live a normal life, and the power to decide who gets a lollipop at the end of the appointment. Use it wisely.