Plexon’s “Following Protocol”

Linear Probe Discussion with Prof. Dr. Pascal Fries

My question is for beginners, which probe would you recommend for optogenetic simulations, and how many channels are minimum for reasonable recordings?

“So I guess this now pertains to the laminar probes from Plexon, we have clearly the best experience with V-Probes, we have also tried S-Probes, in our hands, the unit recordings are particularly crisp with V-Probes, I think generally the S-Probes have been recommended for penetrating the dura, I showed you that at least with this approach that has been developed in my lab by Eleni Psarou, we can use a… guide tube and we can reliably penetrate the dura even though we are typically not
scraping the dura and then the V-Probes give us the best neuronal recordings. We also like them because at the tip they have the smallest dimensions, so of course, with these probes, there’s always a bit of a cost that you pay with each penetration there’s a tiny little damage so the smaller the damage the better and so the V-Probes are basically this the slimmest at the tip there they have the smallest footprint. I think the other question was how many channels…”

Do you implant ECoG arrays below dura? Have you compared epidural and below dura responses?

“Yes, so in the awake macaque monkey we have implanted them subdurally I
know that the lab of Andreas Kreiter has implanted them epidurally, and from him, I take that epidurally he can also get a defined receptive field but an overall signal to noise ratio that is substantially lower than if you put them subdurally. Now I have to say that if you put them subdurally you can record for a certain time but at some point, the dura is encapsulating typically the ECoG…”

Do you think the optogenetic induced gamma in cat striate is similar to an arousal input, for example, electrical MRF stimulation, as shown in 1996 and 2004 by Singer and colleagues?

“Absolutely so you’re referring to the work of Matthias Monk
when he was in the Singer lab that was at the time when I was also a Ph.D. student there. So well, so the gamma induction itself is not due to the mesencephalic reticular MRF stimulation, but gamma is induced simply by visual stimulation or when we drive the circuit optogenetically then we just see gamma. MRF is a modulating system or maybe under anesthesia it could be enabling but it is not, so the picture that I think I would draw is that the cortical circuit at least in the awake state is very prone at least in the visual cortex to generate gamma if you excited there is sufficient excitatory drive then the tight interaction between the excitatory neurons…”