The Brain and Emotion

In 1938, B. F. Skinner proposed that all of behavior reflects reaction to rewards and punishments (reinforcers) provided by the environment. He believed that the voluntary behavior of organisms is shaped by these reinforcing events and thus operates under selective principles similar to those proposed by Darwin for the origin of species. In this treatment of the brain mechanisms of reward and punishment, Edmund Rolls illustrates how far we have come in elucidating the mechanisms by which such selection works. Skinner was forced to rely on the reflex principle for his chief mechanism, a brilliant if necessarily crude proposal for a one-to-one correspondence between stimulus and response. What lay in between was irrelevant because it was not available for objective analysis. For Rolls, the workings of the brain are no longer hidden. The step-by-step process by which stimulus valence is represented in higherlevel systems for taste and for vision is beautifully laid out in Chapters 1 and 2 of this important volume. Rolls argues that the reward value of stimuli are tied, not to their crude sensory analysis, but to high-level sensory representations of objects that reflect their invariant properties. Rolls begins with the mechanisms that code reactions to food, but the approach clearly generalizes to all sensory systems. The largest portion of the volume is devoted to the brain mechanisms related to emotion. In Chapter 3 emotion is defined in terms of the reaction of the organism to rewards and punishments, the brain systems underlying processing of emotion are described in Chapter 4, and the issue of emotion as subjective experience is left until Chapter 9, with its evolutionary significance dealt with in Chapter 10. Defining emotions in terms of rewards and punishments is reminiscent of many efforts in behavioral psychology, particularly those of LeDoux and Mowrer, to understand emotion in relation to the major events in classical conditioning. This ties emotion to stimulus events and makes it much easier to trace the neural systems that respond. However, the earlier work dealt mostly with rodents, whereas Rolls draws upon nonhuman primate and human imaging studies. As a result, Rolls’ book provides a particularly strong treatment of frontal cortical areas and even of the lateralization involved in the coordination of emotion in relation to cognition. Generally, Rolls’ approach recognizes conceptual similarity to the recent effort of LeDoux. However, LeDoux deals mostly with fear, whereas Rolls deals with a larger range of emotions. In his studies of fear conditioning in rats, LeDoux put central emphasis on the amygdala, whereas Rolls also stresses cortical areas. In Rolls’ studies, emotion is not confined to any one brain area, but resides in complex networks whose nodes have distinct functions. In the later chapters, Rolls also attempts to incorporate subjective experience and evolutionary thinking. These sections are likely to be of importance for those interested in a modern analysis of the interaction of cognition and emotion that would allow important but complementary roles for both. According to Chapter 9, consciousness is involved when it is necessary to construct multi-step plans in the pursuit of reward. There are two competing routes to behavior: one fast and based on past reward value; the other slower, conscious and based on calculations of where long-term rewards lie. The attractiveness of this proposal is that it provides some hope that one could connect feelings to conscious thought. However, Rolls’ definition of emotion as related to rewards and punishments limits his treatment of complex emotions and their interactions with cognition, a topic that has been explored somewhat in two other recent books on emotion. The Rolls volume skillfully interweaves detailed accounts of brain anatomy, and ideas from neural network modeling, with examples that might help the reader understand more of their own behavior, including their sexual preferences. This is an impressive achievement. Rolls’ definition of emotions might be too narrow to encompass their full range or to explain why there are differences between individuals and cultures. Moreover, his treatment of consciousness does not begin to capture the full texture of emotional experience. Nonetheless, if you want to understand what is known about a significant part of the study of emotion, this is a book you need to read. There are many recent treatments of emotion; some, I suspect, will sell more volumes, but they may not provide the rewards for the brain in this fascinating book.