According to MacLean, the limbic system served with the most primitive mammals and on the basis of the reptilian complex. MacLean raised it as the structure responsible for the appearance of the emotions associated with each of the experiences on an emotional level.
If a behavior produces pleasant emotions, we will tend to repeat it or try to change our environment so that it occurs again, while if it produces pain we will remember that experience and avoid having to experience it again.
This component would have a fundamental role in processes such as classical conditioning or operant conditioning.