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Is there an emotional brain? (arguments against)


The limbic system has been commonly referred to in scientific literature as the emotional brain. But we know now with more information and advanced technologies that the limbic system is an ambiguous concept, it is what LeDoux says is just a “useful anatomical shorthand”.

One evidence that challenges this theory is that areas that are considered unique to mammals (therefore termed the “mammalian brain”) is also present in ‘primitive’ creatures such as reptiles and amphibians. For example, a study conducted by Gilles Laurent and colleagues in 2018 using single cell RNA-sequencing technology showed that the neurons of the pallium of reptiles had similar genetic makeup to that of the hippocampus and amygdala of mouse and humans! These areas are what MacLean included in the limbic system theory, yet they are present in these ‘lower’ animals. Moreover, the same study showed that the anterior dorsal cortex of the pallium in reptiles was similar to the human neocortex, which is a layer that covers the limbic system and thought to have only existed in ‘higher’ mammals. This goes to show that since animals have different selective pressures, no single group can be thought of as representing the ancestral form of another.

Another piece of evidence is that there are other areas of the brain involved in what we consider as emotion. We see in recent emotion studies that emotion is not localized and is multifaceted. For example, in the famous patient S.M., we see that bilateral damage to her amygdala (limbic area) caused an isolated fear deficit, without involvement in other emotions. Moreover, although S.M. did not recognize fearful faces unless she was told to adjust her gaze to look at the eyes of the subject. Eye gaze is thought to involve various areas such as the inferior temporal lobe and superior temporal sulcus, areas not involved in the limbic system.
Other brain areas have connections to the limbic system and are involved in emotion. These include the hypothalamus that regulates physiological responses and the insular cortex for interoception, a hot topic for emotion researchers in studying the regulation of mood and overall body state.

Moreover, there are areas included in the limbic system that are not specific to emotional reaction. Although the hippocampus is involved in emotional associative learning, it is also involved in declarative memory, explicit memory that does not necessarily involve emotion.

Therefore, it could be suggested that calling the limbic system the ‘emotional brain’ would be misinterpreting the function of these brain regions, as well as oversimplifying the complexity of emotional reactions. As Lisa Feldman Barrett states in her book How Emotion is Made, emotion is a whole-brain process and localizing it to specific regions such as the limbic system is limiting our full understanding of these complex processes.

LeDoux – The Emotional Brain
Gazzaniga, Ivry, Mangun- Cognitive Neuroscience (5th Ed.)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6370519/
https://www.ncbi.nlm.nih.gov/pubmed/7482801
https://science.sciencemag.org/content/360/6391/881.long

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