fiber photometry

fiber photometry
Name	Fiber photometry
Classification	Optogenetics, Calcium imaging, Fluorescence
Uses	Neural activity recording
Inventor	Mark Schnitzer, Karl Deisseroth
Related	Two-photon microscopy, Miniscope, Electrophysiology

fiber photometry is a Fluorescence-based technique for recording population-level neural activity in freely behaving animals. It enables researchers to measure changes in Calcium indicator signals or other fluorescent biosensors through an implanted optical fiber. The method was pioneered by laboratories including those of Mark Schnitzer at Stanford University and Karl Deisseroth at Stanford University, building upon earlier work in In vivo microscopy. This approach provides a critical bridge between cellular-resolution imaging and behavioral analysis, complementing tools like Electrophysiology and Optogenetics.

Overview

This optical method allows continuous, real-time monitoring of dynamic biochemical events within specific brain regions of awake subjects. It is widely employed in Systems neuroscience to correlate neural ensemble activity with behaviors such as learning, memory, and reward processing. The technique's development was facilitated by advances in Genetically encoded calcium indicators like GCaMP, engineered by the Janelia Research Campus and other institutions. Fiber photometry systems are often integrated with behavioral apparatus from companies like Med Associates Inc. and TSE Systems.

Principles and components

The core principle relies on delivering excitation light from a source such as a LED or Laser to brain tissue via a Optical fiber implanted above a region of interest. Fluorescent light emitted by indicators like GCaMP or jRGECO1a is collected back through the same fiber, separated by a Dichroic mirror, and focused onto a Photodetector such as a Photomultiplier tube or Silicon photomultiplier. Key optical components, including lenses and filters, are sourced from companies like Thorlabs and Edmund Optics. Signal processing often involves lock-in amplification to distinguish the signal from background noise, a method refined by the Schnitzer Lab.

Experimental procedure

Experimental implementation begins with a stereotaxic surgery to inject a Viral vector carrying the sensor gene, often an Adeno-associated virus, into a target area like the Ventral tegmental area or Hippocampus. An optical fiber, typically from Doric Lenses or Neurophotometrics, is then cemented in place above the injection site. After recovery, the animal is connected to a flexible patch cord for recording during tasks in setups like the Morris water maze or Operant conditioning chamber. Data acquisition is managed by software such as Bonsai (software) or Synapse (software), with analysis pipelines from Python (programming language) libraries like SciPy.

Applications in neuroscience

This technique has been instrumental in decoding circuit function in disorders studied at the National Institute of Mental Health and the Allen Institute for Brain Science. Landmark studies have linked Dopamine release in the Nucleus accumbens to reward prediction error, work associated with researchers like Naoshige Uchida at Harvard University. It has also been used to track GABA or Serotonin dynamics in models of Parkinson's disease and Major depressive disorder, often in conjunction with the RDoC framework. Projects like the International Brain Laboratory utilize fiber photometry for large-scale, reproducible investigations of decision-making.

Advantages and limitations

Primary advantages include compatibility with freely moving subjects, relatively low cost compared to Two-photon microscopy, and the ability to record from deep brain structures like the Hypothalamus. However, it provides an aggregate signal from many cells, lacking the single-cell resolution of Miniscope or In vivo imaging. The technique is also susceptible to artifacts from movement, Autofluorescence, and photobleaching, challenges addressed by methods from the Boyden Lab at MIT. The implant can cause tissue damage and gliosis, limiting chronic recording windows, an area of improvement for materials from Inscopix.

Related techniques

Fiber photometry is part of a broader toolkit for monitoring neural activity. Two-photon microscopy, used by labs like the Svoboda Lab at Janelia Research Campus, offers superior spatial resolution but requires head-fixation. Electrophysiology, including methods from Neuropixels probes developed at University College London, provides direct electrical recording with high temporal precision. Optogenetics, pioneered by Karl Deisseroth and Edward Boyden, allows for causal manipulation of activity, often combined with photometry in "all-optical" physiology. Emerging methods like Photoacoustic imaging and Diffuse optical tomography offer alternative approaches for large-scale functional imaging.

Category:Neurotechnology Category:Fluorescence techniques Category:Behavioral neuroscience