When we originally submitted our 2008 paper on the orientation selectivity of LFP gamma band activity, the response of one of the reviewers was: “It simply reeks of artefact.” We had found that the LFP gamma band power across our whole array of tetrodes spanning ~1 mm was tuned to the same orientation (give and take) and the preferred orientations hardly correlated with that of the multi unit activity. But after going through many rounds of analysis, I was convinced that our finding was correct and we eventually published the paper.
Nevertheless, I was quite relieved when another group independently obtained the same result: Jia, Smith and Kohn reported in their 2011 paper that for large stimuli (as also used in our study), all LFP sites in an array spanning ~4 mm show the same preferred orientation. In addition, they verified this finding independently with single electrodes and still obtained the same results. Interestingly, they found that when using smaller stimuli, LFP sites exhibit different orientation preferences which correlate well with the multi-unit orientation preference at the site.
Why does this happen? Larger stimuli activate also sites more distant from the recording electrode. Local anisotropies in the distribution of preferred orientations could lead to a net orientation preference even when integrating over such large ensembles. For a more detailed discussion, I refer you to my papers (1,2) and Jia et al. (2011). Interestingly, by the way, the Jia’s paper was published in the Journal that rejected our paper originally based on the assessment that our finding “reeks of artifcat”. For comparison, here are the two figures (top: Berens et al. 2008; bottom: Jia et al. 2011):