April Flowers for redOrbit.com – Your Universe Online
An international team of scientists has shown bio-inspired robots can not only elicit fear in zebrafish, but that this reaction can be modulated by alcohol. These findings, published in PLoS ONE, are the latest in a series of experiments designed to test the ability of robots to influence live animals.
The team hopes to pave the way for new methodologies for understanding anxiety and other emotions, as well as substances that alter them. With this study, Maurizio Porfiri, associate professor of mechanical and aerospace engineering at the Polytechnic Institute of New York University (NYU-Poly) and Simone Macri, a collaborator at the Istituto Superiore di Sanita in Rome, Italy, expand their previous efforts to determine how bio-inspired robots can be employed as reliable stimuli to elicit reactions from live zebrafish. Zebrafish show a strong affinity for robotic members designed to swim and appear as one of their own, according to prior studies. Those same studies revealed this preference can be abolished by exposure to ethanol.
The team hypothesized bio-engineered robots could be used to induce fear as well. They designed a robot that mimicked the morphology and locomotion pattern of the Indian leaf fish, a natural predator of the zebrafish. In a three-section tank, the scientists placed zebrafish in one section, the robotic Indian leaf fish in another and left the third compartment empty. They found the control group avoided the robotic predator uniformly, showing a preference for the empty section of the tank.
The research team exposed separate groups of fish to different levels of ethanol in water to determine whether alcohol would affect fear responses. In humans, rodents and some species of fish, ethanol has been shown to influence anxiety-related responses. The team observed remarkable changes in behavior, (failing to avoid the predatory robot), in the zebrafish exposed to the highest concentrations of ethanol. No harm or lasting effects have been caused by acute administration of ethanol on zebrafish.
“These results are further evidence that robots may represent an exciting new approach in evaluating and understanding emotional responses and behavior,” said Porfiri. “Robots are ideal replacements as independent variables in tests involving social stimuli–they are fully controllable, stimuli can be reproduced precisely each time, and robots can never be influenced by the behavior of the test subjects.”
To ensure the zebrafish response to the robot was, in fact, a fear-induced response and to validate their findings, the team conducted two traditional anxiety tests and evaluated whether the results obtained therein were sensitive to ethanol administration.
Test subjects were placed in a two-chamber tank with one well-lit side and one darkened side, to establish which conditions were preferable. In another tank, the team simulated a heron attack from the water’s surface — herons also prey on zebrafish. They measured how quickly and how many fish took shelter from the attack. The fish strongly avoided the dark compartment. Most of them sought shelter very quickly from the attack. These responses were significantly modulated by ethanol exposure, abolishing the preference for the light compartment and significantly slowing the fishes’ retreat to shelter during the simulated attack.
“We hoped to see a correlation between the robotic Indian leaf fish test results and the results of the other anxiety tests, and the data support that,” Porfiri explained. “The majority of control group fish avoided the robotic predator, preferred the light compartment and sought shelter quickly after the heron attack. Among ethanol-exposed fish, there were many more who were unaffected by the robotic predator, preferred the dark compartment and were slow to swim to shelter when attacked.”
The scientists believe zebrafish could be suitable replacements for higher-order animals in testing for emotional responses. Their robotic approach would also reduce the number of live test subjects necessary for experiments and may inform other areas of inquiry, from collective behavior to animal protection.