Comparative evidence for the importance of the amygdala in regulating reward salience
Section snippets
Amygdala anatomy and aversion processing
The amygdala is located in the temporal lobe and comprises a complex of subcortical nuclei. In knowledge obtained primarily from rodent studies, it is a major brain region in the neural circuitry of emotion in terms of: inputs received from sensory regions, for example, sensory thalamus, sensory cortex; cellular and microcircuit responding to innate emotional stimuli; learning about and storing memories for the association between neutral to-be-conditioned stimuli and innate emotional stimuli;
Human amygdala for reward processing and in emotional disorder
In human and rodent research, the contribution of the ventral tegmental area-nucleus accumbens (VTA-NAcc) dopaminergic mesolimbic pathway to reward processing [10, 11] and the contribution of the amygdala to aversion processing ([12]; see previous section), have both received considerable scientific attention. It is only relatively recently that the emphasis has started to shift towards recognizing that each of these (and other) brain regions is essential for both reward and aversion
Amygdala for reward including dedicated reward neurons
As in the human case, the small number of rodent studies of amygdala reward processing has yielded affirmative data [19]. For example, in rats it was demonstrated that LA lesion attenuated amphetamine-induced conditioned place preference [20]. Also in rats, subjects underwent sham-lesion or BLA-lesion and were then trained on an operant response-reward contingency and a stimulus-reward Pavlovian contingency, where reward was sweet food. In subsequent tests, BLA-lesioned rats exhibited
Basolateral amygdala reward neurons and the processing of reward salience
Therefore, whilst the critical details of the micro-circuitry of the BLA reward neurons and aversion neurons in terms of topography and projection regions is currently debated, the comparative evidence for existence of exclusively reward-sensitive and exclusively aversion-sensitive BLA neurons is conclusive (Figure 1a). With regards to function these neurons are stated to be emotion-valence specific. It can be hypothesized that in addition to this, within the emotion valence to which they are
Stress, amygdala and reward salience
Chronic exposure of animals to stress in the form of uncontrollable and/or unpredictable aversive stimuli allows for the study of its effects on amygdala function and could well provide important insights into amygdala pathophysiology in emotional disorders. Whilst chronic stress has been demonstrated to induce increased sensitivity to aversion in amygdala-dependent behavioural paradigms, for example, Pavlovian fear conditioning [29] and decreased sensitivity to reward [30, 31, 32], there have
Conclusions
There has been a relative lack of progress in discovering much-needed novel molecular targets and developing more effective treatments for stress-related mental disorders. To a large extent, paucity of knowledge of the neural circuitry underlying major psychological processes accounts for this lack of progress. In particular, this concerns the cellular and molecular changes in specific brain regions impacted by environmental and epigenetic aetiological factors that constitute the
Conflicts of interest statement
Nothing declared.
References and recommended reading
Papers of particular interest, published within the period of review, have been highlighted as:
• of special interest
•• of outstanding interest
Acknowledgements
This review was supported by a grant from the Swiss National Science Foundation (31003A-160147).
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