Fig. 2: The method to compute the mesoscale spike-triggered average and spatiotemporal spike-centered average (st-SCA) between spiking activity and the low frequency component of the local field potential (LFP) during a human focal seizure involves centering and averaging each spike’s associated LFP in both time and space.
a Diagram of the microelectrode array (MEA) placement, a 10 × 10 grid of electrodes of 4 mm × 4 mm in size, was implanted in either recruited territory (blue shading; Patients 1–5) or unrecruited territory (green shading; Patients 6–7). Recruited territory involves a seizure passing through and invading the local cortical tissue, and unrecruited territory is tissue outside the recruited territory but may still be characterized by strong, local synaptic activity3,12. b During seizure activity, the LFPs within the area of the electrode array (the summed LFP of the microelectrode array is depicted in the signal traces) are associated with a multi-unit action potential train. The LFP’s relationship to the spike is considered over time \(\tau \) relative to the spike events. c For each spike across the MEA, its associated spatiotemporal LFP is determined. The red circle in the middle column indicates the spike position on the MEA. Next, the \((x,y)\) axes of the LFP are translated into the \((\xi ,\psi )\) axes, such that the spike position is at the origin. Finally, the results in the right column are averaged to create a matrix that contains the st-SCA. Note that the corners of the average are undefined because the MEA does not have electrodes in the corner positions.
