What Animal Research is Teaching Scientists About the Human Brain
Posted on
Animal research has played a critical role in some of the most important scientific discoveries in history, including identifying the causes and mechanics of diseases, developing vaccines, and understanding how the human body functions.
But animal research has also led to some less critical, though no less interesting, discoveries, and many of those involve how the human brain works in everyday life.
From what happens in the brain when we make educated guesses to what makes us what to snack, these recent animal studies related to thought processes, senses, perception, and behavior have shed light on why humans do what they do.
How We Make Educated Guesses
Researchers at the MRC Brain Network Dynamics Unit at the University of Oxford, by studying both human and mouse brain activity, have determined that brain cells in the hippocampus are able to link memories of separate experiences to enable humans to make “educated guesses,” inferring the answers to questions based on past experience.
According to the study, these links between memories are created in the brain while we are resting or sleeping. The hippocampus is already known to play an important role in learning and memory. To test how exactly educated guesses are formed, researchers created an experiment with mice. They played a sound, then turned on a light. Mice were given a sugar water treat when the light was on. Eventually, the mice began to make the connection between the sound, the light, and the reward.
After a period of rest, however, the mice began making the connection between the sound and the reward, “jumping over” the intermediate step of the light. Forming this new link between the sound and the reward illustrates the way in which the brain creates links between separate experiences to determine which future events will take place.
Persistent vs Reflex Fear
When you see a shadowy figure in a corner of your bedroom, you may still feel aftershocks of fear even after you discover it was just a jacket draped over a chair. This type of persistent fear, which includes physical manifestations including high heart rate and heightened senses, is different from the type of “reflex” fear you get from a less threatening scare, like being startled by a loud noise.
A team of neuroscientists at Caltech set out to determine what happens in the brain cells of mice during the persistent fear state and found that it involves ongoing electrical activity in the hypothalamus.
In the experiment, researchers put a rat in an enclosed space with a mouse and monitored the activity in the ventromedial hypothalamus (VMH), an area of the mouse brain that is encoded for defensive fear behaviors such as freezing and fleeing. When the mice encountered the rat, their VMH neurons were activated and stayed active for tens of seconds even after the rat is removed. Usually, neurons are only active for a few milliseconds.
This is significant because while the hypothalamus is an area of the brain that is thought to deal with more primitive, reflexive responses—receiving a stimulus, reacting, then shutting off—sustained electrical activity is more associated with cognitive functions like learning and problem-solving.
Learning to Avoid Negative Experiences
Scientists at Cold Spring Harbor Laboratory in New York have discovered neurons in the mouse brain that help it avoid negative experiences, and it turns out negative reinforcement and positive reinforcement are closely related.
The “negative experience avoidance” cells reside in the striosome, a part of the brain that was previously thought to be related exclusively to positive motivation—the ability to learn from positive reinforcement and to seek rewards.
The discovery that the striosome also contains neurons related to learning through negative reinforcement reveals the striosome to be a more complex and comprehensive motivation-processing hub in the brain.
The discovery is not only enabling scientists to better understand the connection between positive and negative motivation, it could also help address impaired motivation processing, which is found in people with certain mental illnesses, brain disorders, and neurodegenerative diseases including depression, schizophrenia, Alzheimer’s, and Parkinson’s.
How We Adapt to New Situations
We’ve all been doing a lot of adapting this year, and now researchers at the Brain Research Institute of the University of Zurich have identified the biological process that enables us to adapt to new situations by learning new behaviors.
Using mouse models, the researchers determined that the orbitofrontal cortex, a region of the brain’s cerebral cortex, is capable of reprogramming neurons located in sensory areas.
The discovery was made using an experiment with mice in which the researchers simulated an adaptive, or relearning process and observed individual neurons in the brain during that process. Mice were trained to lick every time they touched a strip of coarse-grit sandpaper with their whiskers and were rewarded with sugar water. The mice were not allowed to lick when they brushed their whiskers against fine-grain sandpaper. If they licked when touched with fine sandpaper, they were punished with an irritating noise.
Once the mice had learned that coarse-grain meant a reward and fine-grain meant a punishment, the researchers reversed the situation, delivering a reward for licking when touched with fine-grain and a punishment for coarse-grain. The mice adapted quickly, learning the new, opposite behavior within a few rounds of reward and punishment. Analysis of individual neurons during this adaptive process revealed that a group of brain cells in the orbitofrontal cortex is especially active during the relearning process. Those cells demonstrated the flexibility to adapt to new situations and modify behavior based on tactile stimuli.
Scientists believe that the process is similar in humans, and may lead to a better understanding not only of how humans replace old habits and behaviors with new ones based on changes in environmental conditions, but also how to help people who have impaired flexibility in decision-making, as with some forms of autism and schizophrenia.
Why We Can’t Stop Snacking
It’s easy to overindulge in snack foods, and new research points to a reason. A mouse study conducted by researchers at the Howard Hughes Medical Institute in New Haven, Connecticut, identified a group of brain cells that influences the palatability of food and drink and prompts animals to keep consuming it.
The cluster of cells linked to snacking are located next to the locus coeruleus, an area of the brain stem that controls attention and motivation. Rather than controlling the urge to look for food, these “snacking” neurons encourage ongoing consumption once food has been found.
The snacking response kicked into high gear when the mice were hungry or thirsty, or when they were indulging in especially tasty or sweet snacks. Understanding the mechanism that makes us keep eating past the point when we should stop could help scientists create a method to stop the cycle in humans.
How We Learn Second Languages
Researchers at the University of Oregon are using mice to understand how humans learn second languages.
One of the researchers in the project had already discovered that learning a new language was more effective when it combined passive learning, like playing Spanish music in the background, with actual practice, like taking a language class. To better understand why that was the case, researchers studied mice to identify how the brain is learning language-related sounds.
In the experiment, mice are trained to respond to different language sounds using a reward system, and researchers observe what is happening in the mouse brain as they hear and learn those sounds.
Once they have developed a hypothesis about what happens during the mouse brain during language learning, researchers hope to apply the knowledge to humans in order to create better learning strategies to enable humans to learn a second language more efficiently.
The brains of mice are quite similar to those of humans, with closely matching architecture and similar types of brain cells, and that has already led to many important discoveries that will improve human health. Those similarities have other advantages—by studying the brains of mice, we might be able to better understand what makes people behave in certain ways, and how to modify that behavior in a beneficial way.