Patient 1. This patient (MRI negative), had incomplete resection of the epileptogenic zone with six postoperative seizures around medication weaning (bottom right seizure chart). Left inferior frontal gyrus (IFG) and orbitofrontal gyrus (OFG) corticectomy showed type 1 dysplasia involving resection margins. (A) Preoperative interictal MSL (top row), ESL (middle row), EMSL (bottom row) suggested medial orbitofrontal gyrus and rectal gyrus (RG) onset with propagation to lateral orbitofrontal gyrus. Early-solutions (left column) for ESL and EMSL preceded early-MSL by 45 ms. (B) Post-operative interictal localization showed a similar pattern of onset and propagation but early-MSL preceded early ESL by 29 ms (early-late-EMSL localized to the superior temporal gyrus). Preoperative, mid-phase solutions (middle column in A) for MSL, ESL, and EMSL fell within the resection bed (magenta shading reconstructed cortex at the bottom of B) and were concordant with ICEEG (A) (red electrodes seizure onset, blue electrodes inactive at seizure onset, yellow electrodes map eloquent cortex for speech, motor) but the medial orbitofrontal gyrus was not covered by the grid; ICEEG position directed by broad fronto-temporal localization given by PET, video EEG monitoring and by lateral inferior frontal gyrus focus given by SPECT (Table 1) and by EEG-fMRI (not shown). The preoperative ictal results (not shown) reflect a similar pattern of discharge onset and propagation. Preoperative ictal early-MSL preceded early-ESL by 14 ms. ESL localized to the anterior inferior frontal gyrus and medial orbitofrontal gyrus while the earlier latency MSL solutions localized to the medial orbitofrontal gyrus and rectal gyrus. Taken together, the results are consistent with a left frontal source starting at the medial orbitofrontal gyrus and rectal gyrus and propagating to the lateral orbitofrontal gyrus and anterior inferior frontal gyrus, the latter supported by ICEEG. The patient is seizure free on re-instituted medication (months 26–39) with consideration of extended resection (involving medial orbitofrontal gyrus) should seizures return. Corresponding averaged waveforms are seen at left margin for MEG (top left, M = magnetometer; G1 = first planar gradiometer; G2 = second planar gradiometer), for HDEEG (middle left), and for combined HDEEG-MEG (bottom left). Corresponding early-phase, mid-phase, late-phase source localization latencies are marked by dotted vertical lines. MGFP (mean global field power) take-offs for HDEEG and MEG are shown at the bottom left corner. Take-off was defined as the first clear disruption of the background that achieved >50% amplitude of preceding baseline activity. The early-phase solution was the first solution to reach 90% explained variance along the millisecond-incremental time-course of the discharge from take-off. sLORETA (standardized low resolution tomographic analysis) current density reconstruction (CDR) maps are represented as F-distribution heat maps, with dominant orientation of distributed sources represented by a dark blue current density reconstruction moving ‘dipole’ (surface negative at spherical end of dipole), at reconstructed cortical surfaces and at MRI scans. HDEEG potentials and MEG fields are shown below the latency bars along with the corresponding SNR value of the signal at the solution time point. EZ = epileptogenic zone; VEM = video EEG monitoring.