The Sahasrara or Crown chakra is about wisdom and being one with the world. When this chakra is open, you are unprejudiced and quite aware of the world and yourself.
If it is under-active, you're not very aware of spirituality. You're probably quite rigid in your thinking.
If this chakra is over-active, you are probably intellectualizing things too much. You may be addicted to spirituality and are probably ignoring your bodily needs.
Chakras are centers of energy, located on the midline of the body. There are seven of them, and they govern our psychological properties. The chakras located on the lower part of our body are our instinctual side, the highest ones our mental side.
Chakras on the midline of the body The chakras can have various levels of activity. When they're "open," they're considered operative in a normal fashion.
Ideally, all chakras would contribute to our being. Our instincts would work together with our feelings and thinking. However, this is usually not the case. Some chakras are not open enough (being under-active), and to compensate, other chakras are over-active. The ideal state is where the chakras are balanced. To find out what the state of your chakras is, do the chakra test.
There exist lots of techniques to balance the chakras. Mostly techniques to open chakras are used. It makes no sense to try to make over-active chakras less active, as they are compensating for other chakras. To restore the compensation they'd be over-active again in no time. To stop them from compensating, the chakras they are compensating for must be opened. See the techniques to open chakras.