Introduction: The traditional circumplex model on the structure of emotion postulates that this process is organized in two basic dimensions: valence (positive negative) and activation (relaxing activating). This model assumes that the valence activates a single evaluative system. With regard to cerebral activity, two ideas are derived from this assumption: 1) a single set of mechanisms and neural circuits becomes activated in response to both positive and negative events, 2) the faculty of response to adverse and pleasant responses (i.e., latency and intensity with which the neural structures involved can respond) is potentially balanced.
Development: We describe the debates on these two issues and, subsequently, the current data regarding them are also described. These data indicate that, in response to aversive stimuli (often noxious), neural systems characterized by their ability to produce an immediate response are preferentially activated. On the other hand, pleasant stimuli (which lead to an approaching behavior towards the stimulus) preferentially activate systems associated with more intense and precise information processing. This is a slower but longer lasting type of activity.
Conclusion: The data suggest that there are separate mechanisms for the evaluation and preparation of a response according to whether the stimulus is negative or positive.