The brain is an incredibly complex system of neurons, synapses and blood flow. It controls all the functions of the body and also regulates the emotional state, but how it processes the feelings people experience is difficult to understand fully. Mental illness is the manifestation of how something can go wrong in the brain, for instance when a person who suffers from anxiety can become stressed over a very minor occurrence that would not normally warrant a fear response.
Researchers at MIT have found new information on a part of the brain and the neurons in that area that transport electrical impulses and other information about events that are pleasant or unpleasant. The amygdala is very small, about the size of a large cashew but it’s responsible for routing crucial signals through the brain. The study is published in the March 31st
issue of the journal Neuron
In a press release about the study Kay Tye, the Whitehead Career Development Assistant Professor of Brain and Cognitive Sciences and a member of MIT’s Picower Institute for Learning and Memory said, “I think this project really cuts across specific categorizations of diseases and could be applicable to almost any mental illness. Learning more about how this information is routed and misrouted could shed light on mental illnesses including depression, addiction, anxiety, and posttraumatic stress disorder.”
This wasn’t the first time Tye and her colleagues have identified certain groups of neurons the process emotions. A paper published in April of 2015 in the journal Nature detailed how the brain handles “good” and “bad” feelings. In that study, they showed how the nucleus acumbens is part of how the brain deals with rewarding experiences, while another group of neurons sends negative information on a pathway to the centromedial amygdala.
Finding out where in the brain these emotions are processed was only the first part of the research. Tye and her colleagues wanted to know exactly what happens in these areas and what the neurons do. Using lab mice, they “tagged” with a protein that reactions with light, called channelrhodopsin . If this protein hadn’t been used, the researchers would not have been able to see how the neurons in different areas connect and carry the signals around. In three groups of mice the team tagged neurons in ventral hippocampus, the centromedial amygdala and the nucleus accumbens.
While the team found that there are no strict boundaries of specific emotions in specific areas of the brain there were some patterns observed. After training mice to associate a specific sound with either a reward of sugar water or a taste of something bitter, they found that in general neurons that directed their signals to the nucleus accumbens, did so as a result of being excited by the reward stimulus.. Conversely, the aversive stimulus of the bitter tasting food caused neurons to project to the central amygdala. This was a continuation of Tye’s earlier research which showed the brain areas that were active during positive and negative experiences, but did not show the actual dynamics of what was happening at the neuronal level. Postdoctoral fellow Anna Beyeler and graduate student Praneeth Namburi were the lead authors on the paper. The video below tells more about the specifics of the study and what treatments could eventually come about from this kind of research.
Sources: Neuron MIT Press Release Nature