BY Paige Comeau ’26
STAFF WRITER
This summer, Assistant Professor of Psychology Dr. Travis Hodges is conducting two different studies involving cognitive bias in lab rats, aided by five student interns and research assistants. Through his research, Dr. Hodges aims to show how a negative bias may develop as a result of stress. The findings of his experiments may help us understand these factors in humans and potentially reveal the mechanisms connecting cognitive biases and depression.
Since his hire in 2022, Hodges has been working on research that aims to connect chronic stress to cognitive bias in rats. Cognitive bias, in simple terms, is the way our brains process everyday situations; a positive cognitive bias indicates a more optimistic outlook, while a negative bias suggests a more pessimistic outlook. In an interview with Mount Holyoke News, research assistant and neuroscience major Emily Steadman ’26 explained the basics of the summer experiments.
The first study, which began during the academic year, is colloquially referred to by Steadman as the cognitive bias age-based study. The study is age-based because Steadman and her peers have tested each rat’s cognitive bias at multiple ages — earlier in the year when they were younger, and now at their current ages — to examine differences that may result from age or experience
To test the rats’ cognitive bias, Steadman and her colleagues put them through a three-week experiment. Twice a day, the rats are taken from their cages, brought on a short walk around the lab and then placed in a shock box where they may be shocked after three minutes. While the arrangement of the shock box, the length of the walk and the time at which they are shocked changes, the rats are always shocked at least once a day. The researchers then examine the rats’ cognitive bias by observing their body language. Rats who try to escape or freeze indicate fear of a shock, showing a negative cognitive bias; rats who act normally do not fear the shock, and thus are theorized to have a positive cognitive bias.
Moreover, Steadman pointed out that by looking at the rats with a negative cognitive bias, researchers get a glimpse of the different coping strategies of creatures under pressure. For instance, she explained that “active coping strategies are looking for a way to escape the shock, whereas passive coping strategies would be just freezing and waiting there.”
As this study’s last three-week experiment comes to the end of its cycle, the researchers are preparing for the experiment's conclusion. After three weeks of this procedure, the rats will be placed in an ambiguous chamber, which does not indicate whether or not they will be shocked. Their reactions, and thus cognitive biases, will be studied.
Following the experiment’s end, the rats will be euthanized via decapitation so that tissue samples may be taken and their brains can be studied. As unsettling as this method may be, Steadman emphasized the importance of the study and the necessity of physically examining brains to complete the work.
Steadman claimed that this method of euthanization, which will be completed via guillotine, was the most humane method available that would not impact the integrity of the research. “It’s the least costly and hopefully the most effective, and with the least amount of pain. We could do [carbon dioxide] tanks, but that wouldn't work without affecting the brain,” Steadman said. “I wouldn't vote for CO2 because it takes a while for [the rats] to go to sleep. This is instant.”
When the brains are dissected, the researchers will look for signs of neurogenesis, which is the increase of neurons in the brain. The more stressed the rat became, implying more negative bias, the more new neurons will have appeared. Interestingly, it is expected that the female rats will show less neurogenesis than the male rats, due to their increased likelihood of experiencing positive cognitive bias. Steadman explained that this difference is likely due to the resilience and high activity levels of the female rats.
The second experiment, which is currently in progress, is referred to by Steadman as the MAM neurogenesis study. MAM stands for Methylazoxymethanol Acetate, a toxin that targets neuroblast development and impedes neurogenesis, which would lower stress levels and create a more positive cognitive bias.
In this experiment, there are three groups of rats. One group is injected with MAM, one group is injected with saline as a placebo, and the other group is injected with nothing, as a control. The two groups of rats which are injected with a solution are then put through a series of tests that subject them to chronic, unpredictable stress.
The rats may be placed in seven different situations to increase their stress levels. These include continuous lighting, isolation, cage rotation, cage tilt, tail pinch and damp bedding. Most often, these tests are concluded after two hours and the rats are returned to their usual state. The researchers check on them after thirty minutes to ensure that they are once again behaving normally.
Steadman discussed the necessity of checking on the rats every ten minutes, particularly those subjected to the tail pinching situation. She “wakes them up and makes sure that they can walk properly and then they go off.”
After three weeks of this continued, semi-unpredictable stress testing, the rats, including the control group, are then put through the same cognitive bias testing as described above. This time, the researchers are looking at how moving the rats from a pseudo-randomized stress procedure to a regulated stress procedure impacts their behavior within the cognitive bias study, as well as the overall effects of the MAM and placebo. This experimentation will end similarly to the first, with the euthanization of the rats and the study of their brains.
Although this position is not for everyone, Steadman emphasized her happiness with the role. Not only is she thrilled to get real-life experience in neuroscience, but also to gain many skills which will be useful in the future, such as organization, collaboration and animal handling.