It is not clear exactly why the conclusions of Xing et al. (2009) differ from those of most other studies, save that of Katzner et al. (2009, discussed below). One noteworthy point is that the LFP Xing et al. (2009) observed was nearly always a negative deflection, regardless of the depth in V1. Like the fact that the LFP and neuronal firing measures reported by Xing et al (2009) gave the same read-out, despite being generated by well-recognized and distinct underlying neuronal processes, this polarity-depth invariance in the LFP is in stark contrast with most other reports; for active cortical regions, transcortical (surface-depth) polarity inversions of “locally generated” LFPs are ubiquitous across sensory areas and independent of stimulus type (Givre et al., 1994;Maier et al., 2011;Mitzdorf and Singer, 1978;Peterson et al., 1995;Steinschneider et al., 2008). It is possible that specific anesthesia effects (e.g., a suppression of normal ambient excitability and variability) may contribute to the findings of Xing et al, even though anesthesia per-se is a common factor in many of the experiments considered above. Similarly the very small dimensions
