They'd hold down on the bar until they propelled their tiny auto to the end of their enclosure, where they collected their reward: Froot Loops.
Lambert and her colleagues at the University of Richmond trained the rats by constantly rewarding them with food every time they moved the plastic auto forward.
"The rat is an appropriate model for the human brain in many ways since it has all the same areas and neurochemicals as the human brain - just smaller, of course", said Kelly Lambert, professor of behavioral neuroscience at the university and a co-author of a paper about the research published October 16 in the journal Behavioural Brain Research.
While acknowledging that human beings are "more complicated" than rats, Lambert said the scientists are searching for "universal truths" about how minds interact with the surroundings to sustain optimal mental health. Three copper bars on the aluminum plate let the rats "steer" the vehicle; when they placed their paws on the bars, the rodents completed an electrical circuit that propelled the ROV, either to the left, right, or straight ahead. The currents powered the vehicle and accelerated in different directions, depending on which bar the rats were holding. Moving the auto forward usually led the rats to a sugary treat of Froot Loops.
Scientist knew the rats were more chill and less anxious when they got to drive the cars by testing their excrement for stress hormones.
That result was reinforced when the rats were given "passengers", with researchers noting that only the animals actually driving the vehicle saw a decrease in stress. The researchers assessed this by measuring levels of two hormones: corticosterone, a marker of stress, and dehydroepiandrosterone, which counteracts stress.
The findings echo earlier work by Lambert that showed lower stress levels in rats that mastered other hard tasks, such as digging to find buried food.
The driving rats in the study held an interest in driving throughout the trial and showed more learning capacity when compared with rats that were less stimulated.
"There are no cures for many psychiatric illnesses like schizophrenia or depression", Lambert said. Professor of behavioral neuroscience, who's the author of the study.
"Beyond the adorableness, there's a real scientific value", he said, noting that the rats likely used various parts of their brains to drive toward their treats.
All rats that underwent training had higher levels dehydroepiandrosterone, indicating a more relaxed state, which could be linked to the satisfaction of gaining mastery over a new skill, referred to as "self-efficacy" or "agency" in humans.
The biggest takeaway for Lambert was the potential for new avenues of treatment the work opened up for people suffering from mental health conditions. She said the task apparently increased the emotional resilience of the animals, and could have implications for humans.