The Dark Side or the Light Side? Ozlem Gunal Neuroscience, Science & Medicine The opening scene of “Star Wars: The Force Awakens” asks this question, a very deep question, one that doesn’t have an answer, still in the seventh movie. Which side would you choose? I know that mice choose the “dark side”. Mice go to dark places because they are nocturnal and they prefer the dark. Their choice is certainly not because of the pernicious power of the dark side of the Force, but what about fear? Does it have an effect on choosing the dark side, as Yoda said? Could there be a scientific common justification of the choice of the rodents and Ben Solo? Mice, with incredible genomic similarity with humans, can show a variety of human-relevant behaviors that could be tested to better understand the human diseases. In one of these tests, fear learning, the mouse is put in a box with two compartments, light and dark. When the mice go to the dark compartment of the box, where they would normally go, they are given a foot-shock and they feel pain, which makes them learn that they shouldn’t go there. Mice tend to avoid such negative stimuli and when they are put in the light compartment after training, it takes longer for them to go to the dark compartment, if they learned. Like humans, rodents can learn to avoid a condition, which they experienced an unpleasant stimulus (such as a foot-shock) before. Rodents can also learn to fear a harmless stimulus, such as a tone, if it is paired with an unpleasant stimulus. In this case they show responses like the ones humans with irrational fears show, such as a change in the blood pressure, or freezing. They show these responses when only the tone is given, without a shock. This learned fear, which is provoked by not real threats can become pathologic for humans, so it is important to understand the mechanisms of this behavior. Over the past 25 years, by using the animal models, significant progress has been made in understanding the brain areas and the connections, which link these areas to emotional functions. What does the aversive stimuli do to the brain and cause fear? Aversive stimuli, as well as visual and auditory stimulus such as facial expressions or noises, change the communication between the brain cells in an area of the brain called amygdala (almond in Latin). This is how fear and its signs (shallow breathing, throat tightness, racing heart, pressure to run away or fight) are produced. Amygdala is required for both learning new emotional situations (acquisition), storing them (retention), and expressing them behaviorally. Apparently amygdala is necessary to stay safe. For mice, it is normally safe to stay in the dark side, but when they learn that the dark side activates fear, they decide not to go. An aversive stimulus, a threat, can cause both fear and/or anger in humans, which both involve in the activation of the brain cells in the amygdala. The amygdala is also connected to several other brain regions. One of them is called the prefrontal cortex, which helps deciding to back off (avoidance) when there is a threat that causes fear. Another brain region is the hypothalamus. When certain brain cells in the amygdala are activated with stimuli eliciting anger, then the activation of the hypothalamus follows, which involves in developing the response to react (aggression). This response leads to hormone release with signs such as heat in the face, adrenalin surge, clenched fists, activated by anger. In this case there may be no activation of the pathways going to the brain areas that have a role in decision making. In the third Star Wars movie, when Luke faces Darth Sidious, we understand how difficult it is to stay at the light side by controlling your anger, fear, hatred, and aggression, which are the stimulants of the amygdala. If the signal from the fear-inducing stimuli passing through cortical areas, which allows us to make decisions, then it is easier to control the fear and anger, and resist to Dart Sidious. If the signal is passing directly to the hypothalamus, indeed “the fear is the path to the dark side”! When the fear learning process does not work, mental illnesses can occur. The deficit in fear learning may be due to neurodevelopmental diseases, but it can also occur in conditions like stress, and the memories may become a source of chronic anxiety. This is because stress may cause a change in the connections between brain cells in certain parts of the brain, and eventually their function. Dark side may be the “quick and easy” path, but there are several factors involved in choosing the sides. There are several brain areas and hormones involved. The type of the cells (if they activate or inhibit another cell) within amygdala, or another brain region. There are connections from all these different cells of amygdala to various brain regions, to all different cells. Even with all this knowledge, it is still not enough to explain why Ben Solo went to the dark side. Maybe it is because the Emperor knows better what amygdala is! If you want to choose for yourself, here is Google’s quiz: http://qz.com/557236/google-lets-you-choose-the-light-side-or-the-dark-side-with-this-star-wars-redesign/ Feature image courtesy of Pixabay.