The Cornell study found that laboratory mice released into a large, enclosed natural field became significantly less anxious. Using the elevated plus maze, researchers measured anxiety before and after a week in the enclosure and observed a marked reduction or full reversal of previously learned fear responses. Authors attribute the change to increased agency and a broader range of experiences and note potential benefits for animal welfare and the generalizability of research, while urging cautious interpretation and further study.
Rewilded Lab Mice Lose Their Fear: Cornell Study Finds Time in Nature Reduces Anxiety
Researchers found that lab mice that were released into a large, enclosed field were almost immediately less anxious.
Laboratory mice often live their entire lives in controlled, sterile environments and are routinely used in experiments that range from cancer research to toxicology. A new study in the journal Current Biology from researchers at Cornell University shows that releasing these animals into a large, enclosed natural field produces rapid and substantial changes in behavior.
The team placed conventional lab mice into a spacious, fenced field near campus where the animals could encounter grass, soil, and a variety of sensory experiences for the first time. After a week outdoors, many of the mice returned with markedly reduced anxiety-like behavior compared with their laboratory baseline.
How Anxiety Was Measured
Researchers used the well-established elevated plus maze to assess anxiety. The maze has two open arms and two closed arms: more anxious rodents prefer the closed arms, while less anxious animals explore the open arms. The Cornell group tested mice in the maze before and after their week in the enclosure.
"The rewilded mice show either no fear response or a much, much weaker response," said Matthew Zipple, the study's first author and a postdoctoral researcher at Cornell.
Even mice that had developed a stable fear response in repeated lab tests showed a reversal after living in the naturalistic enclosure. As Zipple noted, "Living in this naturalistic environment both blocks the formation of the initial fear response, and it can reset a fear response that's already been developed in these animals in the lab."
Why The Behavior Changes
The authors propose that broader, self-directed experiences — what they describe as increased agency — help animals recalibrate how they evaluate threats. In the wildlike enclosure, mice could find their own food, encounter varied stimuli and challenges, and make choices that influenced their outcomes. According to senior author Michael Sheehan, an associate professor of neurobiology and behavior at Cornell, "If you experience lots of different things that happen to you every day, you have a better way to calibrate whether or not something is scary or threatening."
Implications And Caveats
Beyond animal welfare, the researchers argue that rewilding could improve the generalizability of mouse-based research by producing behaviors and physiology that better reflect animals living outside tightly controlled labs. However, the study does not prove direct equivalence to human experience. The authors and outside experts caution that more research is needed to understand mechanisms, long-term effects, and how (or whether) findings translate across species.
Bottom line: A short period in a naturalistic enclosure substantially reduced anxiety-like behavior in lab mice, suggesting that increased environmental complexity and agency can reshape fear responses — with implications for animal welfare and the interpretation of preclinical research.
