The laminar distribution of sensory information conveyed by cortical LFPs
Introduction and Scientific Aim
Local Field Potentials (LFPs) are a massed signal that captures contributions from multiple neural phenomena, and that is sensitive to both supra- and sub-threshold processes. Previous work [1-2] has shown that stimulus encoding by LFPs can provide additional insight into sensory representations beyond that offered by neuronal spike trains and has documented the information content of different frequency components of the LFP . However, little is yet known about how cortical microcircuits at different laminae contribute to the representation of naturalistic sensory information and about the characteristic frequencies of the information representation in each layer. Our aim is to investigate this issue by combining laminar cortical recordings with information-theoretic analysis.
We record laminar LFPs from the primary visual cortex of anesthetized macaques while presenting complex naturalistic movie stimuli. We develop new statistical methods to quantify how the information about the movie stimulus is encoded by the LFPs at different laminar locations and whether LFPs in different layers are tuned to similar stimulus features or share common sources of variability.
Results and Preliminary Conclusions
Our results show that differences in the stimulus-encoding properties of the LFPs recorded at different cortical depths do not simply stem from differences in LFP power. Higher power in an LFP band at a given cortical depth does not translate into higher stimulus-information encoded by that band at that particular depth. This is true, in particular, for the gamma band. Although the power in this frequency range is maximal in the middle layers, the stimulus-information conveyed by gamma power is higher in the top layers. Informative frequencies in the top layers included the gamma and high-gamma ranges while high-gamma carries little information in the bottom layers. Low frequencies are mostly informative in the middle and bottom layers. Our results suggest that LFP oscillations originating from different laminar circuits encode sensory information in a different fashion.
Yusuke Murayama, Stefano Panzeri
 Belitski A, Gretton A, Magri C, Murayama Y, Montemurro MA, Logothetis NK and Panzeri S (2008) Low-frequency Local Field Potentials and Spikes in Primary Visual Cortex Convey Independent Visual Information Journal of Neuroscience 28(22) 5696-5709.
 Montemurro MA, Rasch MJ, Murayama Y, Logothetis NK and Panzeri S (2008) Phase-of-Firing Coding of Natural Visual Stimuli in Primary Visual Cortex Current Biology 18(5) 375-380.
Figure 1 Information about a naturalistic color movie conveyed by the LFP spectrum recorded at different cortical depths. Results are plotted for a representative session (H05391). A) Distribution of gamma power measured at different cortical depth (mean and STD). B) The information conveyed about a complex naturalistic movie by single LFP frequencies at different cortical depths.