As regular readers will know, I’ve been intrigued by the nature of local field potential for some time. There’s a recent paper in Neuron by Lindén et al. that uses a modeling approach to explain the spatial reach of the LFP. This is a subject of some controversy; the spatial reach of the LFP has been estimated at less than 250 microns by some and several millimeters by others. The paper resolves these discrepancies by showing how the apparent integration size depends heavily on these (and several other) factors:
- correlations: if the underlying population is correlated, the LFP reaches further than if the underlying population is uncorrelated
- position of the recording electrode: the greater the difference in depth between the electrode and the location of the synaptic input, the greater the apparent reach of the LFP
So in short, there is no such thing as THE spatial reach of the LFP; it depends on a bunch of things and over an order of magnitude. The paper is fantastically presented, and while I haven’t gone through the methods in details, it looks pretty legit.
If I may so speculate, the widely varying estimates in the literature are probably due to different experimental paradigms. For instance, the reverse-correlation-type experiment used in Nauhaus et al. 2009 might encourage a less correlated population, while the natural images and longer presentation times in Kreiman et al. 2006 may encourage a more correlated population.
It will be interesting to see how their findings are affected once they consider frequency-specific spatial reach, although thismay require making more than a few assumptions concerning the dynamics of the synaptic input. Anyhow, read the paper, it’s good.
Lindén H, Tetzlaff T, Potjans TC, Pettersen KH, Grün S, Diesmann M, & Einevoll GT (2011). Modeling the spatial reach of the LFP. Neuron, 72 (5), 859-72 PMID: 22153380