Decoupling Action Potential Bias from Cortical Local Field Potentials
Figure 2
Example spike and LFP responses for an electrophysiological recording from primary auditory cortex (A1). (a) Brief segment of a raw high-pass filtered signal (black curve, top) and spike events identified by sudden changes in the signal (SUA, circles, and “”s). Green and blue dashed lines indicate, respectively, the thresholds for SUA4 and SUA3 events. Subpanels at right show 100 examples of SUA4 spikes events (a) and the impulse response function that best predicts the LFP (b) from SUA4 (green) or SUA3 events (blue), with standard error indicated by the shading. The dashed blue line shows the SUA3 filter estimate for spike events on a second electrode 0.4 mm from the LFP electrode. The simultaneously recorded raw LFP (black curve, middle) was substantially modified when the component predicted by SUA4 or SUA3 events was removed. The difference between the cleaned and raw LFP signals was the greatest during periods of elevated spiking activity (dashed curves, bottom). (b) The same procedure for removing coupled spike information from the LFP but using multiunit activity (MUA). The MUA signal for the same data segment as in , defined by (2), captured the elevated firing at 0.3 second (red curve, top). The LFP signal with MUA removed (red curve, middle; difference in dashed line, bottom) roughly followed the same pattern as the LFP with SUA removed. The subpanel at right shows the impulse response that best predicted the LFP from the MUA.
