We all know from experience that some pretty terrible people end up in power. But if they're so nasty and incompetent how did they get there?

In the short-term, delusional overconfidence can definitely aid a leader's rise, as can unpleasant behavior. But you'd think that, at some stage at least, merit would matter and the most egregious offenders would be weeded out. Sadly, all too often that doesn't seem to be the case.

New science suggests an intriguing explanation -- it's not that abysmal people rise, it's that once you get power, you tend to become kind of abysmal.

Is power a kind of traumatic brain injury?

This isn't an entirely new insight, of course. Literature and history are littered with examples of the truism "power corrupts." But as Jerry Useem explained in The Atlantic recently, science is adding a new dimension to this age old wisdom by showing that power doesn't just change our behavior, it physically changes our brains too.

When Sukhvinder Obhi, a neuroscientist at Canada's McMaster University, "put the heads of the powerful and the not-so-powerful under a transcranial-magnetic-stimulation machine, he found that power, in fact, impairs a specific neural process, 'mirroring,' that may be a cornerstone of empathy," writes Useem.

That means that "once we have power, we lose some of the capacities we needed to gain it in the first place." he adds.

If that seems extreme to you, Useem's in-depth article is packed with further evidence. Not only do the brain scans of the powerful look different, but decades of research shows that those at the top behave "as if they had suffered a traumatic brain injury--becoming more impulsive, less risk-aware, and, crucially, less adept at seeing things from other people's point of view," he claims.

Even when researchers specifically ask the powerful to try to be more empathetic, they are terrible at it. Which shows that it's not just that those in authority get out of the habit of empathizing, but that they actually lose the capacity entirely.

Lessons for would-be leaders

These are gloomy findings for anyone who hopes to rise to the top and retain both basic human decency and the capacity to understand and connect with others. But thankfully, while power exerts a powerful pull away from empathy, that doesn't mean you can't swim with all your might in the opposite direction.

"Recalling an early experience of powerlessness seems to work for some people," Useem suggests. Another idea is to get "a toeholder" who tugs you back towards reality whenever you threaten to float away on your inflated ego. Winston Churchill's wife, for instance, called him out if he got too big for his britches. PepsiCo CEO Indra Nooyi's mother ordered her go buy some milk when she crowed about her appointment to the company's board. "Leave that damn crown in the garage," added mom.

Another expert Useem talks to suggests "watching documentaries about ordinary people" and "making a habit of reading constituents' [or customers'] letters."

But perhaps the best inoculation against power-induced brain damage is simply knowing it exists. If you're aware that power can seriously erode the skills that helped you to rise in the first place, you're more likely to work hard to stay grounded and compassionate.