From Creatures Wikia
The Concept lobe is the biggest lobe in a Norn's brain. In Creatures 1 it has a size of 640 neurons. The concept lobe is the region of the brain where memories of certain events in a creature's life are laid down and evoked.
This lobe receives input signals from the different sense lobes (via the perception lobe in C1 and C2). One neuron of this lobe may have between one and three input dendrites. All inputs of a single neuron are calculated together with a logical AND operation. This is why this lobe is also called "Combination lobe" in Creatures 3 - it simply combines up to three different inputs to one output.
The output of the neurons in this lobe is passed to the decision lobe. These dendrites may get positive or negative strength values, so they represent what the creature should or should not do in a certain situation.
The dendrite's strength is increased by the "reward" chemical and decreased by the "punish" chemical. Dendrites with a strength near zero may migrate to connect to different active input signals, making new random connections possible.