Visualising an emotional valence map in the limbic forebrain
Jianbo Xiu et al, Chinese Academy of Sciences
Nature Neuroscience, Vol. 17, No. 11, November 2014 www.nature.com/neuro
Summary and review of the above paper
The representation of emotional valences in the brain has long been regarded as a fundamental problem. Emotions are categorised along two dimensions, firstly valence or value ranging from negative to positive, and secondly, salience or intensity ranging from weak to strong.
This paper looks at the activity produced by contrasting emotional stimuli in the limbic areas of the forebrain. The understanding of emotional valences has not made the same progress as has the understanding of sensory representations in recent years, although different patterns of neural activation have been detected for rewarding and aversive signals.
In a study of two strong signals, one rewarding and one aversive, distinct neural ensembles were activated in the forebrain. However, there was also an overlap in the regions activated. Where there was a comparison of rewarding and aversive stimuli the responding neurons were intermingled in the nucleus accumbens. This type of organisation is also seen in the sensory areas.
Rewarding and aversive stimuli appear to be differently coded in the nucleus accumbens. It is suggested that neurons of opposite emotional value may inhibit one another. Where stimuli were both rewarding, there was a greater degree of overlap suggesting the existence of a valence-map. The neural representation of the emotional stimuli appeared to be stable. Thus repeat of the same emotional stimuli activated very similar neural groups, suggesting dedicated neural assemblies for particular stimuli. This is comparable to the encoding of spatial stimuli in the hippocampal region.
Note: Although there are references to the limbic forebrain as a whole, the emphasis of the paper appears to be on the nucleus accumbens reward centre rather than evaluative/decision making areas upstream of this.