Shift register fragility

[Hankslab-ABG]

Greetings,

We're using the 1.0 probes and have noticed that the shift registers are particularly susceptible to failure. Has anyone else had this issue or know of ways to mitigate it?

We first encountered this when implanting probes for chronic recordings in awake, behaving rats. Tissue drag on the probes during implant caused some bending before we were able to break through the pia. After recovery we were never able to get the shift registers to work or register any neural signal.

For a 2nd round of implants we made a larger craniotomy and durotomy, making sure there was ample clearance, no dimpling, and no tissue drag during insertion. We were able to penetrate the pia without any bending and found that the probes passed all tests and yielded excellent recordings. However, after only about 2.5 months of awake, behaving recording (freely moving, no head-fixing) both our rats had the shift registers on their implants fail one shortly after the other. We first noticed this as a dramatic drop in raw trace amplitude and lack of any modulation by movement/behavior and later confirmed via the BISTs that the shift registers were to blame.

We've heard some anecdotal accounts of this happening in other labs, so we're wondering if it's a known issue for animals larger than mice or in freely moving preps where there is more potential for the animal to put stress on the implant via wall collisions, etc.

Thanks very much,

-Adam

[Katarina-Poole]

Hi Adam,

No solution but another anecdotal account. We've also had shift register failure on 4+ of our probes, ranging from a few days after chronic implantation to a few months after which we think is from the shank shearing from some sort of movement (though we have yet to do any histology to check). We also implant in awake behaving ferrets so we run into the issue of head bashing from freely moving as well as being larger animals which may be causing more stress. We haven't found a solution yet - currently trying out enclosures to help better support the probe in the chronic implant, which seem to help but we can't say for certain yet.

Kat

[jenniferColonell]

Two notes about shift register errors:
--The error is due to irreversible damage to the shank -- basically some of the electrical contacts to the site have been lost. Once a probes is showing shift register errors, it's entirely unknown which (if any) site is connected to a given channel.
--If you are running with SpikeGLX and you check the "include probe checks" box by the detect button, the software will run the shift register BIST before each run. It doesn't fix anything, but it will at least alert you that the data isn't valid.