In this review, the authors examine the anatomical and physiological substrates proposed …

• Abstract
• Introduction
• The amygdaloid complex
• Afferent and efferent connections
• Intra-amygdaloid connections
• Morphology and physiology: basolateral complex
• Morphology and physiology: central nucleus
• Morphology and physiology: other nuclei
• Role of the amygdaloid complex
• The amygdala and fear conditioning
• Synaptic plasticity and fear conditioning
• Conclusions
• References
• Figures

Biology Articles » Anatomy & Physiology » The Amygdaloid Complex: Anatomy and Physiology » Conclusions

Conclusions

- The Amygdaloid Complex: Anatomy and Physiology

Studies performed over the last 50 years have clearly establishedthe role of the amygdala in a range of related learning andmemory tasks. The anatomy of the amygdaloid complex, its localconnectivity, and afferent and efferent systems that interactwith the amygdaloid complex are now known in great detail.However, there is a paucity of knowledge of information transferthrough this structure. In addition, although much is knownanatomically about cell types present in most areas of theamygdala, the physiology of cell types has been examined indetail in only a few nuclei. Furthermore, an analysis of thephysiology of local connections within the amygdaloid nucleihas largely been ignored. An analysis of the physiology ofthe local circuitry is essential to elucidate the nature ofinformation processing within the amygdala.

Studies of fear conditioning have provided the most detailedunderstanding of the role of the amygdala and its afferentand efferent connections in this simple learning paradigm.Long-term synaptic plasticity, involving activation of glutamatereceptors within the LA, has been proposed as the mechanismunderlying the acquisition and storage of fear conditioning.However, the types of plasticity that are present and theirunderlying mechanism are just beginning to be studied and ingeneral are not always in good agreement with the behavioraldata. The modulation of processing within the amygdala by neuromodulatorsand hormones that are known to play key roles in memory formation(168, 169) has been largely ignored. A recent report examiningthe changes in synaptic input to neurons in the LA followingodor-induced fear conditioning has found that that the plasticityinduced during conditioning required activation of dopaminergicsystems in vivo (238). It is therefore tempting to speculatethat some of the differences between results obtained in vivoand those seen in vitro might result from changes in the availabilityof some of these modulatory influences.

The major challenge for the future is in the study of the localphysiology and types and properties of receptors and ion channelspresent in the amygdala. Fear conditioning is a relativelysimple learning paradigm, and the involvement of the amygdalain its induction is clear. An analysis of the physiologicalproperties of the circuits underlying fear conditioning willprovide a deeper understanding of the neural mechanisms underlyingthe acquisition and storage of emotionally related memories.These studies will set the foundations for understanding theneurological basis of fear and nervous disorders related tofear.

ACKNOWLEDGMENTS

We thank Dr. Denis Paré and Alexander McDonald for helpful comments on the manuscript and Dr. Paré for providing the data for Figure 9.

M. Lopez de Armentia is supported by a grant from the Secretaria de Estado de Educacion y Universidades (Spain).

Address for reprint requests and other correspondence: P. Sah, School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia. (E-mail: pankaj.sah@anu.edu.au).