What Is the Default Mode Network?

More than half your brain is dedicated to sensory processing. If you hear something monotonous, like our verbial professor giving the lecture, these nerons are getting bored and they want input. So if that professor is droning on and on and on, then your reward system is also bored. It's looking for something new. It wants that unexpected reward. And when something unexpected happens, say, an unexpected reward, then you get an increase in dopum anurgic firing. There's a spike in the dopomine response.