The worm coils backwards as the light excites neurons in the head  (Source: Georgia Tech/Hang Lu)
Red, green and blue lights from a LCD projector switches neurons on and off inside freely moving worms

Researchers from the Georgia Institute of Technology are controlling the muscles and brain of tiny organisms through the use of liquid crystal display (LCD) projector components. 

Hang Lu, study leader and associate professor in the School of Chemical and Biomolecular Engineering at the Georgia Institute of Technology, along with graduate students Jeffrey Stirman and Matthew Crane, have used red, green and blue lights from a LCD projector to switch neurons on and off inside freely moving worms through light-sensitive microbial proteins that were genetically engineered within these worms. 

This new system consists of a modified LCD projector, a microscope, and video tracking. The LCD projector sends a pattern of light onto the worm while the red, green, and blue channels activate cells that react to each specific color. 

This illumination system is then connected to a microscope and coupled with video tracking in order to record the organism's movements and keep the light in position. By doing this, the light's location, color and intensity changes as the organism moves. These changes can be updated in 40 milliseconds or less. 

"Because the central component of the illumination system is a commercially available projector, the system's cost and complexity are dramatically reduced, which we hope will enable wider adoption of this tool by the research community," said Lu.

Lu and the research team began experimenting with the "touch circuit" of the worm Caenorhabditis elegans to see if the illumination system worked. The head of the worm was illuminated as it moved forward, which resulted in a coiling effect where the worm moved in a triangular pattern. Then the light was moved along the body from the head to the tail. When the neurons in the head were "excited" by the light, the worm would move backwards. When the light activated neurons in the tail, the worm moved forward. Other variables changed the worm’s behavior as well, such as the light's intensity and optogenetic reagents excited at different wavelengths. 

"Experiments with this illumination system yield quantitative behavior data that cannot be obtained by manual touch assays, laser cell ablation, or genetic manipulation of neurotransmitters," said Lu.  

In addition, the illumination system can heighten responses to thermal, visual and chemical stimuli. The system is an important advancement in optogenetics, allowing smaller animals to be controlled by light as well. Up until now, systems like this only worked on larger animals.

"This illumination instrument significantly enhances our ability to control, alter, observe and investigate how neurons, muscles and circuits ultimately produce behavior in animals," said Lu.

This study was published in Nature Methods.

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