Turn right at the Light: Physics, Meet Neuroscience!

Turn right at the Light: Physics, Meet Neuroscience! Axonal growth directs the development of the nervous system, and the repair and regeneration of neurons. Chemical and electrical cues are known to guide the growing tips of axons, but a new study published in Nature Photonics reveals that “fluidic shear forces” can also play a role.

• Starting with neurons growing in a straight line for over an hour in culture, scientists created a shearing effect on one side by using a photon-driven micromotor. To do this, they used the birefringent property of calcite beads,held in a laser trap and subjected to circularly polarized light. The result was that the beads started to spin, either clockwise or anticlockwise. This is cool, but the really interesting finding is what happens to the growing nerve tips.

• If a particle was spinning counterclockwise to the left of the axon (fluidic shear runs in the direction of growth), the axon quickly turned left (within ~350 seconds), towards the bead. Conversely, if the particle was spinning clockwise, the axon turned away from the bead. Mirror (opposite) effects were seen with spinning particles to the right of the growing tip. Not all the neurons behaved this way…some just kept going straight, but the results were statistically significant. Variations of the experiment, including changing the orientation of the spin or placing opposite spinning particles essentially confirmed their hypothesis, that the growing tips could sense mechanical force .

• The forces were estimated to be ~0.2 pico Newtons, which is the same order of magnitude detected by the hearing cells in our inner ear.

• What are the practical uses for this light driven,non-invasive technique of guiding nerve growth? “One can envision large arrays of these devices that can direct large numbers of axons to different locations,” the authors state. “This may have the potential for use in vivo to direct regenerating axons to mediate brain and spinal cord repair.”

I’ve attached a 7 second video from the publication ( .mov file, ~400 kb) which takes a minute to load. Please be patient (or tell me how to fix it)! Note the debris moving in the field, which indicates the direction of microfluidic flow .

Abstract: http://www.nature.com/nphoton/journal/v6/n1/full/nphoton.2011.287.html

Nice summary in Science Daily: http://www.sciencedaily.com/releases/2011/12/111220102632.htm

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13 Responses to Turn right at the Light: Physics, Meet Neuroscience!

  1. Rich Pollett says:


    That is some amazing digital footage! Nice summery also. 🙂

  2. Rajini Rao says:


    Did the video work out okay or was there a lag, Rich Pollett ?

  3. Rich Pollett says:


    It ran pretty smooth for me the second time Rajini Rao. I did run it a couple of times.

  4. Rajini Rao says:


    Okay thanks! Yes, this would have been a good candidate for looping. I guess I should learn to edit these things 🙂


  5. I have no idea what this is… Your brain blows my mind !


    Interesting video though… I see things like this if I squint my eyes 😛

  6. Rajini Rao says:


    Haha, Jimmy Shepard , the finger thing is the tip of a nerve cell..the one that makes contact with other nerve cells. It has to know where to go..the early studies were with chemical factors mostly, but this cool study brings up mechanical forces too. I know what you mean about the stuff that floats across your eyes..there’s a technical word for that. Fortunately, I forget. 😀


  7. Thank you… I think I see the light now (some of it anyway).


  8. That’s pretty cool.


    It would be interesting to see physical, electrical and chemical processes combined. The first thing that pops into my imagination is a silicon die with a matrix of calcite beads and transistors etched into it which is submerged in a soup of nutrients. The nutrient soup is specially formulated to break down into different chemicals when exposed to certain wavelengths of light making a sort of photolithographic process for neuron growth possible.

  9. Rajini Rao says:


    Richard Healy , sounds feasible to me! “Caged compounds” are designed to release active chemicals upon light activation. Also, the neurons could express light activated ion channels (“optogenetics”) that can change the electrical gradient across the neuron membrane and thereby change electrical cues. 🙂


  10. controlling neurite direction.. sounds cool


  11. We are touching connections of being where our eternal language flows.

  12. Rajini Rao says:


    Awesome, so glad you enjoyed it Stefania Delprete .

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