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Abstract:
Local field potentials (LFPs) reflect subthreshold integrative processes that complement spike train measures. However, little is yet known about the differences between how LFPs and spikes encode rich naturalistic sensory stimuli. We addressed this question by recording LFPs and spikes from the primary visual cortex of anesthetized macaques while presenting a color movie. We then determined how the power of LFPs and spikes at different frequencies represents the visual features in the movie. We found that the most informative LFP frequency ranges were 1amp;amp;amp;amp;8211;8 and 60amp;amp;amp;amp;8211;100 Hz. LFPs in the range of 12amp;amp;amp;amp;8211;40 Hz carried little information about the stimulus, and may primarily reflect neuromodulatory inputs. Spike power was informative only at frequencies amp;amp;amp;lt;12 Hz. We further quantified "signal correlations" (correlations in the trial-averaged power response to differen
t stimuli) and "
noise correlatio
ns" (trial-by-tr
ial correlations
in the fluctuations around the average) of LFPs and spikes recorded from the same electrode. We found positive signal correlation between high-gamma LFPs (60amp;amp;amp;amp;8211;100 Hz) and spikes, as well as strong positive signal correlation within high-gamma LFPs, suggesting that high-gamma LFPs and spikes are generated within the same network. LFPs amp;amp;amp;lt;24 Hz shared strong positive noise correlations, indicating that they are influenced by a common source, such as a diffuse neuromodulatory input. LFPs amp;amp;amp;lt;40 Hz showed very little signal and noise correlations with LFPs amp;amp;amp;gt;40 Hz and with spikes, suggesting that low-frequency LFPs reflect neural processes that in natural conditions are fully decoupled from those giving rise to spikes and to high-gamma LFPs.
