Combining up to 16 individually adjustable electrodes with optical stimulation in mice

Simultaneously recording and perturbing neural circuits with millisecond-scale temporal precision is a cornerstone of optogenetics research, but the methods for doing so are not always easily accessible. A variety of labs have come up with ad hoc ways to incorpoate fiber optic cables into existing multielectrode implant designs. Very few of these solutions have been documented or published, even though this is becoming an increasingly popular technique. Fortunately, the Moore Lab at Brown University recently published a manuscript on their “flexDrive,” a lightweight implant that can hold multiple fiber optic cables and 16 electrodes (Voigts et al., 2013).

The flexDrive provides a low-weight and high-yield method for chronic electrophysiology. (A) Isometric view of the flexDrive showing the one-piece spring (blue) that acts as the drive mechanism. (B) Illustration of the flexDrive implanted in a 6 month old C57/bl6 mouse. Due to the low implant weight (~2 g), the impact on the drive on natural behavior is minimal. (C) Cross section of the drive and its placement on the mouse skull. In this example, electrodes target the thalamus. (D) Cortical action potentials recorded from a stereotrode (12 µm nicrome wire, gold plated to ~300kΩ) on a flexDrive showing eight clusters (color coded clusters, non-clustered spikes in gray) and average 95% percentiles of the waveforms on two electrode contacts.

The flexDrive provides a low-weight and high-yield method for chronic electrophysiology. (A) Isometric view of the flexDrive showing the one-piece spring (blue) that acts as the drive mechanism. (B) Illustration of the flexDrive implanted in a 6 month old C57/bl6 mouse. Due to the low implant weight (~2 g), the impact on the drive on natural behavior is minimal. (C) Cross section of the drive and its placement on the mouse skull. In this example, electrodes target the thalamus. (D) Cortical action potentials recorded from a stereotrode (12 µm nicrome wire, gold plated to ~300kΩ) on a flexDrive showing eight clusters (color coded clusters, non-clustered spikes in gray) and average 95% percentiles of the waveforms on two electrode contacts.

The basic concept is similar to the designs from Matt Wilson’s lab involving a ring of electrodes, each driven by its own screw (Kloosterman et al., 2009). But it introduces a novel spring-based drive mechanism that significantly reduces both the weight of the implant and the time it takes to build. In contrast to previously published designs (Anikeeva et al., 2011), each of the electrodes on the flexDrive can be moved independently—a feature that is essential for maximizing the number of well-isolated single units that can be recorded.

Comparison between existing types of implants and the flexDrive. Our novel design results in a higher number of individually movable electrodes at a reduced implant weight compared to existing methods. The drive weight of ~2 g enables experimenters to either implant two drives per mouse, or to scale the design to 32 driven electrodes per implant.

Comparison between existing types of implants and the flexDrive. Our novel design results in a higher number of individually movable electrodes at a reduced implant weight compared to existing methods. The drive weight of ~2 g enables experimenters to either implant two drives per mouse, or to scale the design to 32 driven electrodes per implant.

The authors have put a lot of effort into making their designs as accessible as possible. They’ve created a complete online assembly manual, which includes all the design files and a list of parts. Still, labs that don’t have much previous experience building electrode implants might find it difficult to obtain all the components necessary to build the flexDrive. Because so many aspects of the design have been optimized, it requires a number of non-standard parts. It would be nice if the community could figure out a way to eliminate the high barrier to building designs such as this one, perhaps by creating a centralized mechanism for ordering supplies.

References

Anikeeva P, Andalman AS, Witten I, Warden M, Goshen I, et al. 2011. Optetrode: A multichannel readout for optogenetic control in freely moving mice. Nat Neurosci 15: 163-70

Kloosterman F, Davidson TJ, Gomperts SN, Layton SP, Hale G, et al. 2009. Micro-drive array for chronic in vivo recording: drive fabrication. J Vis Exp

Voigts J, Siegle JH, Pritchett DL, Moore CI. 2013. The flexDrive: An ultra-light implant for optical control and highly parallel chronic recording of neuronal ensembles in freely moving mice. Front Sys Neurosci 7

 

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