The experience of emotion—even on a subconscious level—has a powerful influence on the neural faculties responsible for making rational decisions. Evidence for this statement has come principally from studies of patients with damage to parts of the orbital and medial prefrontal cortex, as well as patients with injury or disease involving the amygdala (see Box D). Such patients have in common an impairment in emotional processing, especially emotions engendered by complex personal and social situations, and an inability to make advantageous decisions (see also Chapter 26).

Antonio Damasio and his colleagues at the University of Iowa have suggested that such decision making entails the rapid evaluation of a set of possible outcomes with respect to the future consequences associated with each course of action. It seems plausible that the generation of conscious or subconscious mental images that represent the consequences of each contingency triggers emotional states that involve either actual alterations of somatic and visceral motor function, or the activation of neural representations of such activity. Whereas William James proposed that we are “afraid because we tremble,” Damasio and his colleagues suppose a vicarious representation of motor action and sensory feedback in the neural circuits of the frontal and parietal lobes. It is these vicarious states, according to Damasio, that give mental representations of contingencies the emotional valence that helps an individual to identify favorable or unfavorable outcomes.

Experimental studies of fear conditioning have suggested just such a linking role for the amygdala in associating sensory stimuli with aversive consequences. Indeed, the patient described in Box D showed an inability to recognize and experience fear, together with impairment in rational decision making. Similar evidence of the emotional influences on decision making have also come from studies of patients with lesions in the orbital and medial prefrontal cortex. These clinical observations suggest that the amygdala and prefrontal cortex, as well as their striatal and thalamic connections, are not only involved in processing emotions, but also participate in the complex neural processing responsible for what we consider rational thinking.