Review
Amygdala oscillations and the consolidation of emotional memories

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Abstract

The amygdala receives multi-modal sensory inputs and projects to virtually all levels of the central nervous system. Via these widespread projections, the amygdala facilitates consolidation of emotionally arousing memories. How the amygdala promotes synaptic plasticity elsewhere in the brain remains unknown, however. Recent work indicates that amygdala neurons show theta activity during emotional arousal, and various types of oscillations during sleep. These synchronized neuronal events could promote synaptic plasticity by facilitating interactions between neocortical storage sites and temporal lobe structures involved in declarative memory.

Section snippets

Multiple functions of the amygdala

As a group, amygdala nuclei receive inputs from and project to virtually all levels of the central nervous system (Box 2). Indeed, they have access to sensory inputs of all modalities, and they innervate cortical and subcortical structures involved in functions as diverse as memory, perception, behavioral state control and homeostatic regulation [5]. Accordingly, lesion and imaging studies indicate that the amygdala takes part in wide variety of functions. These include learning in positively

EEG correlates of behavioral states in the neocortex and hippocampus

The neocortex and hippocampus show contrasting activity patterns depending on the subject's state of vigilance.

Oscillations in the BL amygdala

We will now compare oscillatory activity observed in the neocortex, hippocampal formation and BL amygdala during different behavioral states. As the amygdala and hippocampus receive many of their neocortical inputs indirectly by way of the perirhinal cortex [34], we will also consider spontaneous EEG rhythms displayed by this cortical field.

Significance of oscillatory activity

The findings reviewed above indicate that the amygdala reflects a unique pattern of state-dependent oscillations. Like the rest of the brain, focal waves recorded in the amygdala during slow-wave sleep are dominated by waves of high amplitude and low frequencies. By contrast, faster activities of lower amplitude are predominant during wakefulness and paradoxical sleep. Similarities end here however. The lack of sleep spindles in the amygdala, the variable temporal relations seen between the

Conclusion

Compared with the neocortex and hippocampus, the study of neuronal oscillations in the amygdala is in its infancy. However, recent progress indicates that, like these better known structures, the amygdala exhibits a rich repertoire of oscillations. Understanding the role of these oscillations in synaptic plasticity is a major challenge. Undoubtedly, studying the relationship between population rhythms and coding by amygdala neurons will generate valuable insights into this issue. In addition,

Acknowledgements

We thank P. Giguère and D. Drolet for technical support. Supported by research grants to D.P. from the Canadian Institutes of Health Research and the Center for Molecular and Behavioral Neuroscience of Rutgers University. J.G.P. was supported by a scholarship from FCAR.

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