Damasio describes testing the limits of the somatic-marker hypothesis. First, he used skin conductance response to see whether patients with prefrontal damage could still elicit a change in their somatic state. The process involved using various types of stimuli on a patient and running an electric current under their skin to test whether their autonomic nervous system increased the production of fluid from the skin’s sweat glands in response to the stimuli. Damasio found that patients with and without prefrontal damage both had an increase in fluids secretion from sweat glands, indicating a change in their somatic state. However, when confronted with emotional imagery, all subjects without prefrontal damage saw a change in their skin conductance responses, while those with prefrontal damage, including Elliot, did not at all. Even though they could describe the images they saw in detail and knew what types of emotional response would be appropriate, they could not get their bodies to respond to the images. In other words, clinical testing revealed a clear distinction between primary and secondary emotions, which indicated that the somatic-marker hypothesis was worth pursuing.