It’s no secret that each of us have both positive and negative emotions in response to life’s circumstances. In some cases, situations create a sense of pleasure as a result of a favorable experience. Others, however, trigger fear and concern, especially when circumstances threaten our wellbeing. But where do these emotions come from, and more importantly, how do we know when to feel good or bad? While neuroscience has explored many aspects of the brain and thought, sources of emotions remain poorly defined. But thanks to some intriguing new research, it looks like we’re getting a little bit closer to understanding these mechanisms.
As many scientists have expected, both positive and negative emotions originate within the brain itself. But recent findings now suggest specific brain pathways help us determine whether some experience should be viewed favorably or not. In fact, there appears to be a brain switch that allows us to perceive events as either threatening or as desirable. This is intriguing from the standpoint of experiential learning since outcomes can shape these responses. And even more importantly, it’s interesting in relation to certain conditions where this brain switch may be under- or over-reactive. In essence, these new insights could lead to new therapies for a variety of mental health conditions.
“If you have a brain response to anything that is important, how does it differentiate whether it is good or bad? It’s a central problem in the field [of neuroscience].” – Daniela Schiller, Neuroscientist at the Icahn School of Medicine at Mount Sinai in New York City
Emotions and Experiential Learning
When it comes to the way we feel about specific experiences, some are instinctual while others are learned emotions. Inherently, our survival instincts may tell us to run from a predator. Having to learn firsthand that such a threat is not in our best interest would defeat the purpose on most cases. But other times, we gain insights from life’s experiences. We look upon dessert favorably because of the fond memories it provides. And we avoid social environments that cause us to feel anxious or uncomfortable. These are normal learned behaviors that result from the positive and negative emotions we have experienced in the past. But this doesn’t tell us the “how” these feelings develop in the first place.
While neuroscientists have only recently started to explore this subject, they have identified parts of the brain that are important. Many of the deeper parts of our brain, called the limbic system, tend to be linked to emotional reactions. Areas in the brain like the amygdala, basal ganglia, and thalamus are known to trigger specific positive and negative emotions. But it remains a mystery how these areas regulate emotions and determine if an experience should be feared or desired. Understanding these mechanisms is important in order to better identify how to manage mental health conditions that affect emotional responses. If a brain switch could be manipulated through neuromedicine, then these emotional disorders could be better managed.
“The more we know about the neural circuitry underlying emotion and conditioning, the more likely we will be able to build on that to develop interventions [to emotional disorders] in the long run.” – Michael Anderson, Cognitive Psychologist, University of Cambridge
The Discovery of a “Brain Switch”
In order to identify where positive and negative emotions originated in relation to specific experiences, researchers adopted an innovative strategy. Dr. Kay Tye, head of the Salk Institute for Biological Studies, ran an experiment with 2 groups of mice. One group received sugar when hearing a specific tone. The other group received a shock instead to the same stimulus. And by using a technique called optogenetics, the researchers were able to see brain cells that accounted for both positive and negative emotions. Located in the basolateral amygdala, some neurons responded with fear and avoidance when hearing the tone. Other neurons were responsible for positive emotional responses.
While this discovery was intriguing, it still did not identify a brain switch that accounted for different emotional responses. However, the researchers did notice that these neurons had the gene for neurotensin receptors. Neurotensin is a protein that tends to elicit an excitatory and positive response. While this provided a clue about the neural pathways of emotion, it didn’t explain where the neurotensin was coming from. Thus, the researchers then used CRISPR gene editing technology to methodically eliminate neurotensin-producing nerve pathways one-by-one. It was then that they found a brain switch area in the thalamus that determine the positive and negative emotions.
In essence, the thalamus appears to contain a brain switch that determines positive and negative emotions associated with an experience. The thalamus is a perfect location for this since it serves as a relay for incoming sensory inputs. If the sensory input is deemed desirable, the thalamus produces neurotensin that causes a positive response in the amygdala. If the sensory input is considered a threat, then neurotensin is not produced. This results in an unfavorable emotion associated with the experience in the amygdala, which is its default state. Without question, this is rather complex to say the least. But this is what makes the discovery of this emotional brain switch all the more amazing.
“[The thalamus] is at the hub of where we translate sensory information into motivational significance. In evolution, it’s going to dictate whether you survive. In our modern-day society, it will dictate your mental health and your quality of life.” – Dr. Kay Tye, head of the Salk Institute for Biological Studies in La Jolla, California
The Discovery’s Potential for the Future
Notably, much more research will be required to examine this thalamic brain switch in more detail. But from a theoretical perspective, it offers potential for the future in managing conditions like addiction and depression. For example, in addiction, the positive emotions linked to a behavior are excessive. This triggers repeated use behaviors that result in destructive health outcomes. By blocking neurotensin at the amygdala, this positive emotional reward linked to the behavior might be reduced. At the same time, depressed individuals might benefit from a neurotensin enhancer. By creating more positive feelings linked to events, a depressed response would be less likely. Without question, the field of emotion neuroscience is quite new and in its infancy. But its promise is quite grand, and the discovery of the emotional brain switch in the thalamus looks to be just the start.