The Future of Neurological Tools: Sonogenetics

One of the topics I was interested in was Dr. Steidl's talk on optogenetics. Optogenetics is a great tool that lets us turn neurons on or off with various pulses of light. As the contents of our toolbox grow, the opportunities for neuroscience continue to grow. The microbial opsin method shows that light-induced inward cation currents may be used to depolarize the neuronal membrane and positively modulate firing of action potentials, whereas optical pumping of chloride ions can induce outward currents and membrane hyperpolarization, which negatively modulates the firing of action potentials. These tools may be used to target specific subpopulations of neurons within tissues, which is very useful. However, our tools are still expanding and we have discovered a new method to control neurons.

An article in  The Guardian talks about the advent of "sonogenetics", which allows the use of ultrasound to activate brain, heart, and muscle cells from outside the body. Scientists have bred worms with genetically modified nervous systems that can be controlled by bursts of sound waves. The nematodes change direction the moment they are blasted with sonic pulses that are too high-pitched for humans to hear. This happens because the pulses switch on motor neuron cells that are genetically modified to carry membrane channels that respond to ultrasonic waves. The worms do not normally respond to ultrasound, but they do when surrounded by a fluid containing microscopic bubbles. These bubbles seem to amplify the ultrasonic waves which then pass inside the worms.

The amplified ultrasound waves act on structures known as TRP-4 ion channels, found in the membranes of some of the worms' cells. According to a report in Nature Communications, the sound waves make these ion channels open up and activate the cells they are attached to.

This procedure has advantages to optogenetics, in that optogenetics requires light to be sent down an optic fiber to the desired location inside the brain, whereas low frequency ultrasound waves can pass through tissue unhindered, and can be sent into the brain from on top of the skull.

Demonstration of Sonogenetics