Beyond Mickey: how mice help humans understand addiction
When studying for classes, students often try to find shortcuts that help them quickly grasp as much information as possible. Even though it can be difficult to achieve that goal, neurologists and psychologists are finding new ways to help humans learn more efficiently. For many years, scientists looked at how the brain learns new things, but now they are looking at what the brain chooses to focus on.
Research conducted at Stanford University, funded in part by the Wu Tsai Neurosciences Institute’s Neurochoice Initiative, analyzed where, when and how the brain decides what to learn.
The study — released Oct. 26 by assistant professor of biology and senior author Xiaoke Chen, who is also a member of Stanford Bio-X and the Wu Tsai Neurosciences Institute — may one day help researchers understand how humans learn and better yet, may assist in treating drug addictions.
The researchers observed how the mice understood their surroundings during the experiemnt. Mice must learn about the sights, sounds and sensations all around them, and how the information they learn changes over time.
From this, researchers gathered that the paraventricular thalamus, which usually controls our emotional processing and adaptive responses to stress, serves as a kind of gatekeeper, making sure that the brain identifies and tracks the most salient details of a situation.
“We showed thalamic cells play a very important role in keeping track of the behavioral significance of stimuli, which nobody had done before,” Chen said. The results are astonishing, as Baruch College finance major and freshman Samuel Yusufov stated in an interview with The Ticker. “Who knew the thalamus can be this sophisticated and be a huge factor in deciding what the brain learns,” he said.
In the beginning of the study, Chen and colleagues used classic reinforcement to associate specific odors with either bad or good consequences. Mice were reinforced to think that one odor meant water was coming, whereas another odor conveyed to the mouse that it was about get a puff of air to the face.
Next, the researchers replaced the puff of air with a mild electric shock. As a mouse got shocked, the team saw that the neurons in the PVT tracked that change. In the air-puff phase, two-thirds of PVT neurons responded to both orders, and an additional 30 percent were initiated exclusively by the odor-signaling water.
In contrast, throughout the electric-shock phase, the balance shifted. Nearly all PVT neurons responded to the shock, while about three-fourths of them answered to both bad and good outcomes. Once the mice were full by the water, a similar shift occurred. The mice didn’t need water any longer, so therefore the PVT responded less to the water-signaling odor and more to the air puff-signaling odor. This implied that the mice were more responsive to bad outcomes than good outcomes. Furthermore, the results displayed the PVT tracks identify what is most important in a particular moment — the good can outweigh the bad and vice versa.
In additional experiments, the mice were genetically modified so the researchers could control the PVT with light. Using this method, the team believed it could strengthen learning. For example, the team wanted to teach mice more quickly that an odor no longer signaled water was coming or that another odor had switched from signaling water to signaling a shock.
“Neuroscientists also now have a new way to control learning,” Chen said.
Learning is a result of feedback. However, humans and animals need to have the ability to differentiate what is considered feedback and what is considered noise. This experiment can help with cognitive research tremendously.
According to the Stanford Medical School blog Scope, “They also point, in the long run, to ways to help treat drug addiction, Chen said, by helping addicts unlearn the association between taking a drug and the subsequent high.”