. I present a hypothesis concerning the neuronal, mental and behavioral effects of all kinds of affective (emotional) stimuli, i.e., of unpleasant and pleasant stimuli. I use the term stimulus in its broad sense. Affective stimuli evoke two associated percepts: ?cognitive? and ?affective?. A food in the mouth, for example, evokes the gustatory percept and the percept of pleasure. However, affective percepts are unstable parts of cognitive-affective compounds. Five types of affective percepts are pain, fear, pleasure, ?desire? and appetite in the broad sense of these words. Desire is evoked by inadequate pleasant stimuli. Affective percepts are ?lower? or ?higher?. The latter are not directly associated with bodily needs. Esthetic and social percepts are higher, for example. Although pain and pleasure are essentially innate, they can be modified by sensory experience. Alimentary and esthetic preferences and social values are modifiable, for example. The neurons of pain and fear and of the unpleasant components of desire and appetite motivate four types of voluntary actions. These are, respectively, escape, avoidance, ?optimization? and approach actions. All these actions eliminate the motivating displeasure. In addition, avoidance actions protect from the signaled pain, optimization actions increase the existing pleasure and approach actions provide the signaled pleasure. Thus, voluntary actions associated with different percepts occur according to one universal principle. Voluntary actions are ?internal? and behavioral. During internal actions a goal and then an action plan are decided. These actions often provide the images of the goal stimuli and of particular movements.