Muammar Qaddafi is insane. His actions, like the actions of countless dictators and cult leaders before him, seem inhuman. He has gone from 'bad person' to 'barely sentient'. All hints of conscience, even consciousness, seem to be fading. It is if a bizarre alien has taken over his brain.
It has now become a cliche to say, "Power corrupts. Absolute power corrupts absolutely." Here's the original quote:
I cannot accept your canon that we are to judge Pope and King unlike other men with a favourable presumption that they did no wrong. If there is any presumption, it is the other way, against the holders of power, increasing as the power increases. Historic responsibility has to make up for the want of legal responsibility. All power tends to corrupt and absolute power corrupts absolutely. Great men are almost always bad men, even when they exercise influence and not authority: still more when you superadd the tendency or certainty of corruption by full authority. There is no worse heresy than that the office sanctifies the holder of it. ( Lord Acton )
Research in psychology, most famously the Stanford prison experiment, confirmed this. Power makes people act very badly. Even a hint of power can do the same thing.
Recent research and theoretical developments in neuroscience explain why humans do this. People used to think that humans had large brains in order to understand and deal with the natural world and to make tools. But it does not take much brainpower to use tools, and brains are very metabolically expensive. Also, we know that humans are not, instinctively, very good at using tools and solving problems. So we need a new theory to explain why people have such large brains.
The Social Intelligence Hypothesis says that humans have large brains in order to manage social relationships. There is a very large advantage to working in a large, well-coordinated group, and this advantage is what drove the development of larger brains. Casual observation supports this theory. Most normal people instinctively employ social strategies that are amazingly sophisticated from a mathematical game-theory point of view. The same people who struggle with basic arithmetic will often do things in their social life that our best and most sophisticated mathematical models can barely replicate. For example, people will spread gossip in order to test and monitor the social connections of their peers
The key to human coordination is our theory of mind. This is, briefly, the ability to imagine that other people have their own thoughts, desires, and knowledge. We are the only species that has a well-developed theory of mind, although other social animals like dogs and wolves have somewhat similar abilities.
In order to imagine and predict the thoughts of others, we have to be able to analyze our own thoughts. It is very hard to model how others might be thinking just by collecting data from the world. Even our best computers and our best analytical techniques, supplied with mountains of data, will take a long time to estimate anything just based on data with no guiding theory programmed in. It is much, much easier to be able to look at your own thoughts, ask yourself why you did what you did, ask yourself what you would do in an imaginary situation, and then assume others might act in a similar way. In other words, consciousness mainly exists because it is a useful social tool.
This analysis of our own thoughts, and our ability to see ourselves as part of a larger society, is perhaps the most defining feature of humanity. But there are two things to keep in mind. The first is that the 'consciousness process' is grafted onto an animal brain, and it is not essential for maintaining life. The second is that the human body is amazingly lazy. Most things that are not regularly will atrophy. This applies to muscles, bones, connective tissue, and also neurons and their connections. Any mental process that is not used will be shut down.
So is perfectly possible for consciousness, like any other mental skill, to wither away from disuse. Now remember that consciousness exists only to navigate society. In order to get things from others, you have to interact with them. For almost all people, getting what you want means keeping other people happy. But what happens when you can get whatever you want without having to care about what other people are thinking? If you are in a position of power, you do not need to navigate social complexities. You just tell other people what to do and they do it. There is no need to activate your social intelligence.
With this background knowledge, the corrupting nature of power becomes more clear. People who are in power for an extended period of time start to lose their theory of mind. They lose the ability to analyze the thoughts and desires of others. There is no need to analyze and reflect on their thoughts, so they simply stop doing it.* Over time, their brains simply stop bothering to be conscious, or even human. They are left with nothing but animalistic desires and an ability to use language to express those desires.
Or, put simply:
Power means not having to think about what other people think. Sentience is thinking about what other people think. Therefore, more power means less sentience.
An extended period of power will literally make someone inhuman.
*Note that people who have lots of power, but bigger ambitions, do not suffer this. If you are the absolute and unchallenged ruler of a country, but you want to make your country larger and more powerful, you will have to constantly analyze the thoughts of the people in the surrounding countries. You will make alliances and deals with neighboring rulers, and this will keep your brain exercised. Conversely, people who have a tiny amount of power, but who are unchallenged in that tiny sphere and have no desire for anything else, can suffer these mental effects.