Tapered Optical Fiber Performs Multisite Photometry in the Brain

Researchers from Istituto Italiano di Tecnologia (IIT), the University of Salento, and Harvard Medical School have developed a light-based method to capture and pinpoint neural activity in the brain. The new method allows signals from various brain regions to be collected simultaneously through the use of a tapered optical probe.

The approach relies on bringing fluorescent molecules into specific nerve cells to track their electric activity and measure the level of neurotransmitters. To achieve this, the team used a tapered optical fiber that could capture light from single neurons and enable light collection over an extent of up to 2 mm of tissue and multisite photometry along the taper.

The researchers inserted the light-sensing probe inside the striatum, a region of the brain involved in planning movements, and used the probe to track the release of dopamine, a neurotransmitter involved in motor control that also plays a role in the development of disorders like Parkinson’s disease, schizophrenia, and depression. The device successfully captured neural activity in specific subregions of the striatum involved in the release of dopamine during specific behaviors. Using a single tapered optical fiber, the researchers simultaneously observed distinct dopamine transients in dorsal and ventral striatum in freely moving mice performing a simple behavioral conditioning task.

This is a representation of the tapered fiber able to detect simultaneous optical signals from different neurons. Courtesy of Antonio Balena (IIT).

The new approach has allowed scientists to capture how nerve signals travel in time and space and gauge the concentration of specific neurotransmitters during specific actions. The researchers said that collection volumes from the tapered optical fibers could be engineered in both shape and size by microstructuring the nonplanar surface of the taper, to optically target multiple sites not only in the deep brain but potentially in any biological system or organ in which light collection is challenging because of light scattering and absorption.

The team believes that its work could enrich researchers’ methodological repertoire and could provide a foundation for finding new ways to map connections across different brain regions — an ability that could lead to the design of devices to image various regions of the brain and even treat conditions that arise from malfunctions in cells inhabiting these regions.

The work was led by Ferruccio Pisanello at IIT, Massimo De Vittorio at IIT and the University of Salento, and Bernardo Sabatini at Harvard Medical School. The research was published in Nature Methods (www.doi.org/10.1038/s41592-019-0581-x).