Growing new brains with infrared light
University of Texas Arlington scientists have discovered a way to control the growth or repair of neurons and neuron circuits, using a non-invasive “neuronal beacon” (near-IR laser beam) — essentially rewiring brains, or even creating new ones.
This major discovery,published in Optics Letters, promises to enable several new applications, UT Arlington assistant professor of physics Samarendra Mohanty said in an exclusive interview:
- Building highly precise 3D neural circuits in-vitro as a model for future supercomputers using neuromorphic chips (or even using the neurons themselves in an artificially grown biological computer).
- Brain activity mapping, in combination with precision stimulation and imaging tools such as the fiber-optic, two-photon, optogenetic stimulator and label-free phase imaging developed by Mohanty.
- Repairing damaged neurons in the peripheral nervous system by rewiring around lesions (for patients with spinal-cord injuries, for example).
- Rewiring circuitry of the brain in the future, correcting for damaged or diseased neurons and neural circuits (the near-IR laser beam can penetrate deeply and non-invasively).
Guiding axon growth
In a core discovery, Mohanty found that axon growth can be precisely controlled by shining a near-IR laser near the axon. This “neuronal beacon” process generates localized heat, causing the axon to change its growth direction in about 10 minutes. He found that axons can sense surprisingly low temperature rises (gradients) of less than 0.1 degrees C generated locally with a near-infrared laser.
Mohanty’s team performed optical-guidance experiments using cortical neurons isolated from embryonic 18-day rat embryos. A laser with beam power of 80 mW was reported, with a wavelength of 785 nm (700 to 1000 nm, and power of several orders of magnitude lower, also worked, but visible light caused damage to the axonal growth cone). The beam was placed ~5 µm away from the axons’ filopodia, asymmetrically positioned in the path of the advancing growth cone.
Creating neuronal networks
In the paper in Optics Letters, the authors say this neuronal-beacon method can be easily extended to form a neuronal network in-vitro by spatio-temporal control of the laser beam.
“This can be achieved by use of scanning laser beams or sculpting the laser spots by diffractive optical elements [like lenses], SLMs [spatial light modulators], and even standard light projectors.
“Being able to form in-vitro neuronal circuitry with high fidelity by the non-invasive photonic-guidance method described here will allow us to probe the functions of basic building blocks of the neuronal network.”
The neuronal circuitry can be augmented by ultrafast near-IR “laser scissors” for nanosurgery of undesired connections — silencing specific neurons or neuronal elements (axon, dendrite, spine) in the circuit. In combination with optical stimulation and imaging tools, this will enable all-optical testing of the computational nature of the neuronal circuit.”
Mohanty earlier demonstrated that the near-IR laser also allows for light-sensitization of neurons by transfection of opsin-encoding genes, and also for two-photon optogenetic stimulation and optical imaging. Mohanty believes rapid progress can be made in the all-optical control of neuronal circuit formation, and activity and mapping functional networks of the brain.