Tennessee is an especially fertile place to study twins.
It’s the main reason why Jonathan Schaefer, assistant professor in Vanderbilt University’s Department of Psychology, relocated here in 2023 to continue his research on the environmental determinants of mental health.
The state flags twins in its birth data, making them easier to find and — hopefully — add to the local twin registry Schaefer and his team are building. The registry currently stands at around 200 members (100 sets of twins), and Schaefer tells the Scene he’d like to reach as many as 1,000 sets of Tennessee-born twins to call on for various twin studies.
While only identical twins share the same DNA, even fraternal twins are good subjects, as they typically grow up in the same household, are parented by the same people, share the same socioeconomic status as children, go to the same schools, and even often have overlapping friend groups.
Schaefer focuses much of his research on mental health and cannabis use, which isn’t suitable for a traditional randomized trial. He can’t make one group use cannabis every day and deny the other group from ever trying it, for example.
“Rather than asking a question like, ‘Are people who use cannabis more likely to experience depression?’ I can ask a slightly different version of that question,” Schaefer says. “If I look at twins who differ in their cannabis use, does it seem to be the case that the twin that uses more cannabis is more likely to become depressed? That’s a much, much more powerful question.”
Ankita Mohan and Ali Sloan, both second-year doctoral students studying in Schaefer’s lab, are co-leading the first study using the growing local twin registry. They’ll focus on how childhood experiences — particularly adversity — shape mental health and behavioral outcomes in young adults.
The first question: Is the experience of two twins different enough to make sense for this study? If they’re having the exact same experience, it won’t work, Sloan says. For example, if one twin was bullied but another wasn’t, researchers can track any problems that might be caused down the line. One goal of the study is to encourage intervention after children have adverse experiences in the future.
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“We already know that childhood experiences are really important in shaping development, and that adverse ones are linked to a wide range of negative outcomes,” Sloan says. “We also know that most people who experience difficult things are resilient, and that [raises] this interesting question of: Why do some people experience negative outcomes, but others don’t, when in theory, they may have had similar experiences growing up?”
Schaefer also has a research question around use of artificial intelligence: Is using AI causing mental health problems, social isolation or issues with cognitive offloading? If we start to delegate cognitive tasks to technology, we may become worse at those tasks, he hypothesizes. (As an example, he explains that using GPS hurts people’s navigation skills.) Another study from Mohan at the lab will look at AI use and mental and behavioral health outcomes, particularly in people with ADHD.
Twins have been key in psychological studies for decades, Schaefer says. The Minnesota Twin Family Study, which started in 1989, is one well-known example. Schaefer’s lab uses that data to draw new conclusions too.
Using current technology, Schaefer thinks the data collected through the new Tennessee twin registry could be stronger than before. Researchers get better answers about frequency of alcohol or cannabis use if they can ask on a weekly basis, and that data is easier to collect via smartphone than in person.
“I think that the difference with our research is that there aren’t too many of these twin studies that have really taken advantage of the fact that now we’re in the digital age,” he says. “Everybody has a cellphone, everybody has access to Zoom. We could do a lot of these assessments remotely.”
As explored in the 2018 documentary Three Identical Strangers, identical siblings have been used in unethical studies in the past, in an effort to truly isolate the impact of nature versus the impact of nurture. Modern studies like those in Schaefer’s lab still explore how much genetics and environment play a role in mental health problems like depression, substance use, anxiety, schizophrenia, autism or ADHD.
“The big finding from that line of research — over years and years and across lots of different problems — is that it’s almost always both [nature and nurture],” Schaefer says.
One thing researchers observe about twins: They seem especially open to studies like these. Sloan has already recruited more than 50 participants for her pilot study in the course of a week.
“I think it’s because they understand there is something special and unique about being a twin, and so if they can use that to help out science, on average, they seem to be willing,” Schaefer says.
