SHINING A LIGHT ON THE BRAIN
Discover how scientists are using optics and genetics to unveil the brain's secrets.
November 1, 2023 by Ewa Zarnowska
There are as many as 100 billion neurons in the human brain* and so much that we’ve yet to understand about how they all work together to create the thinking beings that we are. Neuroscientists are seeking answers to big questions about how the brain functions, how the nervous system develops, and how we can better understand and treat neurological and psychiatric disorders.
An essential tool for neuroscience researchers, optogenetics is a technique that encodes light-sensitive proteins into specific types of neurons to make them responsive to light.
This novel method lets scientists accurately turn neurons on or off, helping to uncover their part in essential brain processes like learning and memory. These processes can be affected in various diseases.
In optogenetics, when researchers shine light on neurons containing opsins, it can trigger these cells to activate or deactivate. This change mirrors the fundamental way neurons in the brain communicate, through action potentials.
The All-Optical Approach: Bridging Gaps in Neuroscience
The timing of action potentials carries specific information, and optogenetics holds the promise of uncovering this encoded information and to decode how the brain operates. While early optogenetics experiments utilized fiber-delivered LED light, the precision of light delivery has significantly improved with lasers, particularly femtosecond lasers, which provide three-dimensional precision for photo-stimulation.
By merging optogenetics with multiphoton imaging, researchers developed the transformative "all-optical approach," where a laser is used to stimulate (or silence) specific neurons and a second laser beam is used to map activity in other interconnected neurons by sensing changes in their fluorescence characteristics. This sensing often uses a fluorescent calcium ion indicator since these ions map changes in metabolic activities, including the action potential.
This method, compared to previous techniques, provides a comprehensive and detailed perspective of cell activities with the option of single-neuron resolution.
Plus, it does this without the invasiveness or limitations of older, electrophysiological techniques.
Today, neuroscience researchers can capture the synchronized activities of hundreds of cells as animals exhibit natural behaviors.
Additionally, researchers aim to interfere with the activity of specific cells firing action potentials during the animal's behavior using optogenetics to confirm their significance in the observed behavior.
These cells, despite belonging to the same circuitry, may be situated at different depths in the brain. Special tools have been developed to adapt optical setups to simultaneously target these cells.
Commonly, a highly dispersive spatial light modulator is employed to create multiple laser beamlets for volumetric multiphoton optogenetics, each beamlet targeting a different specific neuron. The effectiveness of light perturbation relies on simultaneous multiphoton imaging to monitor changes in the intensity of fluorescence signals from sensors, which reveal cell states (active or inactive).
Coherent Pioneers Solutions for Optogenetics
In all-optical multiphoton experiments, the most frequently used pairs of actuators (opsins) and sensors are red opsins (sensitive to wavelengths around and above 1000 nm) and green indicators (sensitive to wavelengths around 900 nm). This spectral separation minimizes any potential crosstalk between the photostimulation and fluorescence imaging processes.
The field of designing new fluorescent probes for multiphoton microscopy is continually evolving, with a particular focus on spectral tuning. Red-shifted light penetrates more deeply into tissues, is less energetic than blue-shifted light, and causes less photodamage. This can be particularly advantageous when opsins are combined with fluorescent labels and voltage and calcium indicators to reduce crosstalk.
To facilitate complex all-optical experiments, Coherent offers a broad portfolio of femtosecond lasers for multiphoton optogenetics and imaging.
For those diving into all-optical multiphoton experiments, Coherent femtosecond lasers are indispensable.
Products like the Coherent Monaco LX and the Coherent Axon 1064 aren't just state-of-the-art; they're specifically designed to cater to varied research needs and budget constraints.
Each laser in our repertoire brings unique capabilities, ensuring that researchers have the precise tools they need.
Optogenetics: A Beacon of Hope for the Future
The horizons of optogenetics stretch far and wide. On the medical front, it holds the promise of evolving into targeted treatments for debilitating conditions like epilepsy, Parkinson's, and even depression.
Beyond medicine, it has the potential to revolutionize brain-computer interfaces and neuroprosthetics. This could be life-changing for individuals with paralysis or other neurological conditions, offering them newfound ways to interact with the world.
Learn more about Coherent solutions for optogenetics.
