Common and Distinct Neural Mechanisms

Emotions are generally thought to arise through the interaction of bottom-up and top-down processes. However, prior work has not delineated their relative contributions. In a sample of 20 females, we used functional magnetic resonance imaging to compare the neural correlates of negative emotions generated by the bottom-up perception of aversive images and by the top-down interpretation of neutral images as aversive. We found that (a) both types of responses activated the amygdala, although bottom-up responses did so more strongly; (b) bottom-up responses activated systems for attending to and encoding perceptual and affective stimulus properties, whereas top-down responses activated prefrontal regions that represent highlevel cognitive interpretations; and (c) self-reported affect correlated with activity in the amygdala during bottom-up responding and with activity in the medial prefrontal cortex during top-down responding. These findings provide a neural foundation for emotion theories that posit multiple kinds of appraisal processes and help to clarify mechanisms underlying clinically relevant forms of emotion dysregulation. How do emotions arise? Do they arise via low-level processes that provide quick, bottom-up affective analyses of stimuli? Or do they arise via high-level, top-down cognitive appraisal processes that draw upon stored knowledge? This has long been one of the most contentious issues in the field (Lazarus, 1982; Zajonc, 1984), and these opposing viewpoints have only gradually yielded to a synthetic perspective holding that both types of processes are important for emotion generation (Scherer, Schorr, & Johnstone, 2001). BOTTOM-UP AND TOP-DOWN PROCESSES IN EMOTION GENERATION Despite the long history of interest in this issue, direct evidence of separable bottom-up and top-down processes in emotion generation is remarkably scarce. In part, this is because behavioral studies that have been the coin of the realm for much of the field’s history measure only the inputs to and outputs of emotion-generation processes and, as a consequence, cannot specify which particular processes were involved in generating a given emotion. Researchers in other areas have dealt with this type of problem by using neuroscience methods to clarify the mechanisms underlying processes of interest (Kosslyn, 1994). Although neuroscience methods have a similar potential in the domain of emotion, to date neuroscientists have focused primarily on the bottom-up processes involved in simple forms of affective perception, learning, and memory (LeDoux, 2000; Phelps, 2006). In so doing, they have successfully identified brain systems—such as the amygdala—involved in the learning and bottom-up triggering of emotion in various species. But they have paid less attention to cognitive processes involved in top-down emotion generation (Wager, Barrett, et al., 2008). Although neuroimaging studies have begun to examine top-down processes, they have not been designed to distinguish the relative contributions of bottom-up and top-down processes to a given emotional response (e.g., Phelps et al., 2001; Teasdale et al., 1999).