Comparing the emotional brain of humans and other animals

By some accounts, the human emotional brain seems to extend up from the amygdala, whereas the emotional brain of nonhuman animals seems to extend from the amygdala down. Affective neuroscience studies of humans have tended to focus on particular regions of the neocortex and adjacent structures (e.g., prefrontal cortex, cingulate cortex, and amygdala in the temporal lobe). By comparison, affective neuroscience studies of nonhuman animals focus more often on subcortical brain structures (e.g., amygdala, nucleus accumbens and mesolimbic projections, hypothalamus, ventral pallidum, septum, brainstem). But the emotional brain is not really so different between humans and other animals. This chapter reviews the roles of various cortical and subcortical brain structures, and shows that each structure plays a similar role in humans and animals. Instead, the apparent difference in emotional substrates is due largely to differences in the goals and procedures of studies of humans and animals. Human affective neuroscience studies have emphasized cortex because they study highlevel emotional cognition (rather than more basic emotional reaction), because they study correlational relations (rather than causal relations between brain activity and emotion), and because their techniques are better suited for detecting cortical than subcortical involvement. Animal studies have emphasized subcortical structures because they focus on basic types of emotional reaction (rather than emotional cognition), and on the neural causation of those emotional reactions (rather than brain activation correlated more widely correlated to emotion, but not necessarily causal). The emotional brain of humans is different from that of other animals in only one major respect: the degree of encephalization of function, or spread of emotional processing upwards into cortical circuits, and in the consequent ramifications of increased cognitive involvement in human emotion. The result has not been to move the human emotional brain from subcortical structures to cerebral cortex, but rather to raise the level of cortical interaction with subcortical circuits of emotion.