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Optogenetics as a technique to manipulate defined-neuronal activity with light has two main advantages: 1) Millisecond Temporal Precision and 2) Genetically-Defined Spatial Precision

Temporal precision enables researchers to turn neurons on or off with millisecond timing. This fast timing can closely mimic the firing rates of neurons in the brain.

Spatial precision enables researchers to manipulate the activity of explicit genetically-defined neuron populations (e.g. inhibitory neurons). This provides a direct causal link between the manipulation of the genetically-defined population and the variable being measured.

In optogenetic experiments, only neurons expressing the optogenetic probe are stimulated leading to activation or inhibition of specific neural activity (depending on the probe expressed).

However, standard optogenetic light sources can only illuminate the entire field of view and, as a result, stimulate all neurons expressing the optogenetic probe. Such a system may be adequate  for some experiments in which all optogenetic-expressing cells are stimulated at the same time, but more advanced experiments may require the specificity to selectively stimulate individual neurons.

The ability to illuminate select neurons within a population of optogenetic-expressing neurons is called cellular-resolution optogenetics (1). This method requires more sophisticated spatial specificity to selectively stimulate individual neurons within an optogenetic-expressing population.

Comparison between widefield and cellular-resolution optogenetic stimulation.

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The ability to illuminate certain individual neurons is not a limitation of optogenetics per say, but a limitation of the standard optogenetic light sources used in most optogenetic systems. Standard light sources can only illuminate all cells within the field of view, and they have no ability to control where they illuminate to target individual neurons.

The development of spatially targeted light technologies have enabled researchers to control where the light illuminates the sample (technologies for cellular-resolution optogenetics will be discussed in a later post), such as an individual cell, making cellular-resolution optogenetics possible (2). For example, a digital micromirror device (DMD), such as Mightex’s Polygon, allows researchers to illuminate multiple select individual neurons or regions simultaneously to perform cellular-resolution optogenetics.

Cellular-resolution optogenetics has multiple applications in the field of neuroscience. For example, scientists can study neural circuits and decode neural patterns at the level of individual neurons (3,4). These types of studies have been carried out both in vitro and in vivo using different technologies (1,3,4,5). The experimental applications for cellular-resolution optogenetics is endless.

Next Post

What Systems are Available for Cellular-Resolution Optogenetics? (Part 1) Galvo-Scanning

References

  1. Shemesh, OA et al. (2017). Temporally Precise Single-Cell-Resolution Optogenetics. Nature Neuroscience, 20(12), 1796-1806.
  2. Ronzitti, E et al. (2017). Recent Advances in Patterned Photostimulation for Optogenetics. Journal of Optics, 19(11).
  3. Anastasiades, PG et al. (2020). Mediodorsal and Ventromedial Thalamus Engage Distinct L1 Circuits in the Prefrontal Cortex. BioRxiv.
  4. Tran, M et al. (2019). Neocortical Inhibitory Interneuron Subtypes Display Distinct Response to Synchrony and Rate of Inputs. BioRxiv.
  5. Chen, IW et al. (2019). In Vivo Submillisecond Two-Photon Optogenetics with Temporally Focused Patterned Light. Journal of Neuroscience, 39(18), 3484-3497.

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