Scientists have developed a system that creates 'virtual taste' by controlling neurons with light.
The system was successfully applied on flies, enabling them to experience sweet taste while feeding on bland gelatinous goo.
The tool optoPAD, developed by researchers from Champalimaud Foundation in Portugal, combines two high-tech elements.
The first is optogenetics, a powerful method that uses light to control the activity of neurons -- turn them "on" or "off".
In the experiments, flies found the bland food more appetising because its sweet-sensing neurons were activated by exposure to green light.
The second element of the optoPAD is an additional system, previously developed in the lab, called flyPAD.
"The flyPAD uses touchscreen-type technology to monitor the fly's feeding behaviour. 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," said Jose-Maria Moreira, one of the researchers in the journal eLife.
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By combining flyPAD with optogenetics, researchers were able to overcome one of the main challenges in the field of feeding research: precisely controlling taste sensations.
Unlike auditory or visual information, which can be altered instantaneously and independently of the animal's behaviour, animals only experience taste information when they voluntarily touch the food with their tongue, or proboscis.
"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 said.
The study shows that the optoPAD is able to effectively pair active feeding with optogenetic manipulations, and that these virtual tastes have a very real effect on the behaviour 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.
Though optoPAD seems like a fantastic way to improve one's nutrition without compromising taste, the researchers' goal is to use this technology to improve human life in a more fundamental way.
"The food we eat affects all aspects of our lives, including ageing, ability to reproduce, lifespan, mental state and mood," said Carlos Ribeiro, from Champalimaud Centre.
"Yet, how the brain controls food choice is still a mystery. The optoPAD can help us identify the neurons and genes that may have a direct impact on nutrition and hence our well-being in years to come," said Ribeiro.