Milan Halgren, Orrin Devinsky, Werner K Doyle, Helene Bastuji, Marc Rey, Rachel Mak-McCully, Patrick Chauvel, Istvan Ulbert, Daniel Fabo, Lucia Wittner, Gary Heit, Emad Eskandar, Arnold Mandell, Sydney S Cash
Review posted on 21st November 2017
Congratulations on the great paper! Very impressive work.
There are some inaccuracies which I thought would be good to point out. I can imagine that some people thought this represents the first 'solid evidence' about the brain mechanisms of alpha because it is stated in the manuscript that previous papers use a global reference? This is not the case for our 2014 PNAS paper. For the laminar recordings we referenced to the metal shaft of the probe, which is right next to the contact sites, giving something like a bipolar LFP. We compared this with a silver/silver chloride wire in the recording chamber (as also noted in the paper), which didn't change the results. Furthermore, the crucial finding that implicated the involvement of layer 5 in the alpha rhythm (figure 4 of the PNAS paper) are based on CSD and MUA signals, for which the reference is not relevant. The V1-V4 data (not V2 as mentioned in the discussion) used bipolar LFP signals as well.
Also, it might be good to note that only in early visual areas alpha has been shown to be strongest in the deep layers. In particular, Bollimunta, Chen, Schroeder and Ding J. Neuroscience 2008 showed that alpha was only strongest in the deep layers for V1 and V4, but in the superficial layers in IT.