Negative brain: an integrative review on the neural processes activated by unpleasant stimuli.

Evolutionary pressure has led the nervous system to guarantee rapid and intense responses to negative events (dangerous, harmful or repugnant). Thus, the 'negative brain' (the set of neural mechanisms triggered by unpleasant or negative stimuli) is equipped with several specific characteristics. This review organizes the current data on the human negative brain in three blocks. Firstly, the "Input mechanisms" block describes those structures responsible for the rapid distribution of all sensory information. Secondly, the "Evaluation systems" block refers to the key pieces: those responsible for evaluating negative consequences of stimulation and deciding which response is the most appropriate for coping with them. Thirdly, the "Associated and output processes" block describes how evaluative elements may interact with other brain structures to modulate attention, store and recover situational information, activate defense/withdrawal motor programs (or plan new actions) and develop autonomic/motor actions to cope with the unpleasant event. Finally, an integrative summary that serves as a tentative model of the negative brain is provided.