Tranel et al. (20003 gives a succinct definition of higher level brain functions in their chapter abstract:
Higher brain functions are the operations of the brain that stand at
the pinnacle of evolution and are largely unique to humans. Verbal
communication, the ability to “think in the future,” and the capacity
to hold multiple tracks of complex ...
The Neurons become refractory which means that they can't fire again until time has passed. Look up Action Potential and the limits of firing rating.
There is also a competition for different circuits to become conscious so when one becomes tried the other takes over. This is why it is hard to continue to think about one thing, without soon considering ...