Balancing and unbalancing of the pleasure processes in the brain. In the normal brain, wanting, liking, and learning processes are balanced over time (column 1). The breakdown of the balance between these processes can lead on the one hand to anhedonia (the lack of pleasure 'liking'), or of avolition and apathy (the lack of incentive salience 'wanting'). On the other hand, an opposite imbalance can lead to addiction or related impulsive-compulsive motivation disorders (excessive incentive salience 'wanting'). The above depicts a progressive decrease in both wanting and liking (column 2) which is markedly different from an addictive increase in wanting, which can induce excessive motivation even if there is a decrease in liking (column 3). This has been proposed to be the case in addiction (Robinson and Berridge 1993).