What part of the brain is responsible for monitoring incoming information and alerting higher brain areas?

The right answer is the reticular activating system (RAS).

The Reticular Activation System. This is an element of your brain that is useful for capturing your attention and for achieving your goals more easily.

Let's take an example immediately to illustrate what the RAS really means: A loudspeaker announces your name and asks you to pick up your daughter at the reception. And there, your brain, your RAS gets in motion: your attention is at its highest level and you distinctly and clearly distinguish the message and its content addressed to you.

Thus, thanks to the RAS, which starts automatically in your brain, the relevant information is brought to your attention. The RAS plays a role of intermediary, a filter between the conscious part and the unconscious part of your brain. The latter can not store all the information, it is necessary that a relevant sorting is done between them. It's the RAS that does it. It is he who decides what is worthy of attention and what is not. As soon as it judges that information concerns you to the highest degree, he will "wake up" your brain that will absorb it. Thus, as part of our example, the RAS has been instructed to wake up your attention as soon as your name is spoken in the speaker.