ReviewThe amygdala and appraisal processes: stimulus and response complexity as an organizing factor
Section snippets
Background: the intrices of Pavlovian fear conditioning
Pavlovian conditioning has a long and illustrious history, starting from its namesake and continuing today [44]. Based on the immense literature addressing the behavioral characteristics of Pavlovian conditioning, it is the paradigm of choice for research on the neurobiology of learning and memory, and it constitutes the general methodological framework of the present review.
One form of Pavlovian conditioning that has received considerable attention in neuroscientific studies over the last
The amygdala and fear conditioning: the significance of circuitry
Since the discovery that lesions of the amygdala produce altered social responses in a variety of conditions [25], a role has been ascribed for the amygdala in associating stimuli with specific outcomes, such as an impending fearful situation. It is well embedded within contemporary views of emotional learning that the amygdala plays a pivotal role in the formation and consolidation of aversive memories formed during fear conditioning [9], [27], [38].
The amygdala is a multinuclear complex.
The complexity dimension as an organizing factor of amygdala circuitry: a hypothesis
Given that the processing of a tone may be considered simple because of its unimodal and discrete nature, whereas the processing of a background context may be more complex because it is multimodal and temporally diffuse ([3], [12], [14], above discussion), we would like to argue that the functional dissociation in the amygdala could be based on the differential processing of elemental versus configural association. If this is true, then B may function as a primary amygdaloid processor for
Implications of the complexity hypothesis: remodelling associative fear conditioning
Based on investigations of the neural basis of fear conditioning in rodents, prevailing theories of amygdala refer either to the LA (e.g., Ref. [40]) or the entire BLA complex (e.g., Ref. [66]) as the principal site of convergence of neural pathways that carry information about CSs and USs. The above evidence and discussion imply, however, that this conception needs to be modified when discussing complex, configural CSs, such as an environmental context. In particular, it must be considered
Beyond S-R: an extended role of the amygdala
The amygdala integrates information from the external and internal milieu and has direct output connections to nuclei that control physiologic, autonomic and behavioural fear-induced responses. The evidence discussed thus far suggests that a consideration of the complexity dimension of motivational stimuli as well as that of the emotional responses may contribute to our understanding of the functional anatomy of the amygdala. What is clearly missing in the picture as presented, however, is how
Conclusion
The results reviewed here support the notion that functionally dissociable amygdala subsystems are involved in associative processes underlying aversive and possibly, appetitive emotional behavior. We suggest that in this dissociation, a complexity dimension may be an organizing factor both of input and output pathways of the amygdala. Yet, the potential variability of emotional responses to motivational stimuli of varying degrees of complexity assumes an important role for intra-amygdala
Acknowledgements
The authors thank Prof. Joseph LeDoux (NYU) for valuable comments.
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- 1
Present address: Center for Neurobiology and Behavior, Columbia University, New York, NY 10032, USA.
- 2
D.Y. and A.D. contributed equally to the work.
- 3
Present address: The Weizmann Institute of Science, Department of Neurobiology, Brain Research Building, Rehovot 76100, Israel.