For decades now the standard approach to stimulating human nerve cells has been to use the method used by the human body itself – electrical current. Electrical stimulation of nerves is quite effective, but also comes with significant drawbacks including damage caused by the physical contact from the electrodes and the inability to stimulate at a small enough granularity, thereby causing undesired stimulation of nearby cells.
Recently researchers have devised an alternative solution to nerve stimulation: zapping them with a laser beam. Laser based nerve stimulation overcomes many of the problems associated with electrical stimulation: it requires no physical contact with the nerve cells and the laser can be tuned to precisely hit only the nerve cells that are desired. Laser based nerve stimulation could unleash a revolution in our ability to interface with nerve cells. For example, the precision offered by laser interfacing with human nerves may aid efforts to develop prosthetic limbs that are as dexterous as real human limbs.
This breakthrough in laser based nerve stimulation has created a flurry of press in recent months. In addition to the ieee article referenced above, another excellent article came from the researchers published by Spie. Interestingly, the exact mechanism by which laser light is able to cause neuron stimulation is unknown, as quoted here by the Spie article:
A conceptual understanding of how laser light stimulates neural tissues is crucial for the further optimization of the technique, allowing it to reach its full potential. The current hypothesis—based on a number of mechanistic experiments—is that the laser activates nerves by a transient, thermally induced mechanism. At the stimulation threshold, experiments suggest that the maximum nerve-surface temperature increase is less than 9°C, well below the 45–50°C tissue temperatures required for the onset of tissue damage. Future experiments will reveal if stimulation arises through a direct membrane interaction or an indirect effect leading to membrane depolarization.
The article offers a fantastic picture that demonstrates the superior nature of laser based stimulation over electrical stimulation in its ability to target only the desired nerve cells without accidentally stimulated nearby neurons. In the picture below we see that the electrical stimulation caused the target nerve to stimulate but also caused unwanted stimulation of nearby nerves. The laser based stimulation avoided this unwanted stimulation.
