amygdala and emotion

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Vol. 6, No. 2, April 1996

The amygdala and emotion

[Review article]

Michela Gallagher, A Chiba

Current Opinion in Neurobiology 1996, 6:221-227.

Outline

Abstract

Abbreviations

Introduction

Emotion and amygdala damage in humans

Studies of associative learning in humans with amygdala damage

The modulation of memory after amygdala damage

Studies of fear conditioning in the rat

Specialized function of amygdala subsystems in associative learning

Conclusions

Acknowledgements

References and recommended reading

Copyright

Abstract

The amygdala complex has long been known as part of the neural circuitry

critical for emotion.

Beyond its role in emotional reactivity, studies of animal models and

patients with amygdala damage

demonstrate its importance in emotional learning, whereby cues acquire

significance through

association with rewarding or aversive events. Although its function in

associative learning has

become well established, other recent research has advanced the concept

that the amygdala

regulates additional cognitive processes, such as memory or attention.

For example, a

correspondence in the function of the amygdala has recently been shown

in the modulation of

memory in humans and laboratory animals. The use of animal models has

progressively defined the

circuitry for these functions within the amygdala and its

interconnections with other brain systems,

including pathways through which the amygdala modulates memory and

regulates attention. These

various lines of research are progressively advancing our understanding

of the amygdala's role in

providing linkages between affect and cognition.

Abbreviations

CS-conditioned stimulus;

SCR-skin conductance response;

US-unconditioned stimulus.

Introduction

Emotion encompasses a wide range of experience and can be studied in a

variety of ways, ranging

from verbal descriptions to the measurement of covert physiological

responses, such as heart rate. A

potentially useful framework for neurobiological studies is provided by

a model in which emotions

are considered along two dimensions [1]. On one dimension, emotional

states range from positive

(e.g. happy or confident) to negative (e.g. fear or anger). These

different emotional states, in turn, are

associated with different behavioral tendencies. In the case of positive

emotional states, there is a

tendency towards attraction or approach. In contrast, aversion and

defense are associated with

negative emotional states, in which withdrawal, escape and avoidance are

likely to occur. A second

dimension of emotion is arousal. Both positive and negative emotional

states can range on this

dimension from relative calm to high degrees of arousal. Consideration

of these dimensions of

emotion is useful in determining the neural circuits involved.

In their initial study of temporal lobe damage in nonhuman primates,

Klüver and Bucy ([2]; see also

[3]) described a loss of emotional reactivity, characterized by a

relative absence of arousal and a

change in behavioral responses to emotional stimuli. They observed that

monkeys with damaged

temporal lobes (including the amygdala, the hippocampal formation, as

well as the non-limbic

temporal cortex) were generally placid and approached objects that they

would normally perceive as

threatening. A similar pattern of hypoemotionality is commonly described

in clinical case reports of

human patients with amygdala damage[4]. Such effects of amygdala damage

suggest a global

function in the regulation of emotion. However, recent research,

discussed in this review, indicates

that distinct circuitry within the amygdala subserves specific aspects

of emotion, differing with respect

to behaviors regulated by negative and positive emotional states.

Moreover, distinct circuitry

underlies the control of arousal by the amygdala, providing evidence for

a dissociation in the arousal

and valence dimensions of emotion.

Emotion and amygdala damage in humans...

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