Researchers from Lisbon, Portugal has developed a system that utilizes virtual reality to control neurons that control taste. Their study involves  a starving fly that consumes a not-so-delicious food because of the appearance of a green light and then stops eating when the green light disappears.

"The fly's experience was very real. It was a virtual taste created by directly manipulating its taste neurons," says Carlos Ribeiro, Head of the Behavior and Metabolism lab at the Champalimaud Centre for the Unknown in Lisbon, Portugal.

He and his team developed the optoPAD that simulates virtual taste realities that can manipulate the behavior of the fly. This technology is published in a the journal eLife. 

Two elements comprise the optoPAD. Optogenetics is the method that uses light to control the neuron's activity by controlling them with on or off. The fly in the study enjoyed food because its neurons that control its taste were activated by the green light. 

The second element is the flyPAD which was previously developed by the team, as well. "The flyPAD uses touchscreen-type technology to monitor the fly's feeding behavior. Just like your phone is able to detect the touch of your finger on the screen, flyPAD is able to detect whenever the fly touches the food", explains José-Maria Moreira, one of the leading co-authors of study.

One of the main concerns in the field of feeding research involves the precise control of taste sensations. This was resolved through the powerful combination of optogenetics and the flyPAD. 

The main difference between auditory or visual information with taste is that the former can be manipulated independently while the latter requires the subject to touch the food voluntarily with its tongue or proboscis for flies. 

"With optoPAD, we are constantly monitoring the behavior of the fly, to ensure that we optogenetically change the taste of the food precisely when the fly is in contact with it", Moreira explains.

"In this study, which shows that the optoPAD is able to effectively pair active feeding with optogenetic manipulations, the researchers demonstrate that these virtual tastes have a very real effect on the behavior of the flies. For instance, they are able to make the fly eat excessively by optogenetically activating sweet-sensing neurons; or make the fly stop eating all together, regardless of how hungry it is, by optogenetically activating bitter-sensing neurons," according to the study. 

The researchers were not convinced of just manipulating taste. "We developed the optoPAD, because we are interested in understanding how the brain makes one of the most fundamental decisions for our health: what food to eat", says Dennis Goldschmidt, another leading co-author, "but food choices do not only depend on taste, many parts of the brain are involved, so we wanted to ensure that optoPAD can be used to study the activity of neurons anywhere."

Findings of the study show that neurons, regardless of location, can be studied to understand their role in how the brain works.