Fig. 2.

Laminar field potential profile and CSD analysis of epileptiform events. A, A representation of the experimental scheme. A stationary (reference) electrode was located in layers V–VI while another electrode (moving) was advanced from the pial surface (layer I) to the deep layers [angular bundle (AB)] in 50 μm increments. B, Field potential profile of the first 60 msec of an SDE recorded at the layers noted. The superimposed traces at the toprepresent the field potentials recorded at the level of the reference electrode at all levels shown and were used to align the traces recorded from the moving electrode. The latency from the onset of the peak negativity in layers V–VI to layers III and II was 3.0 and 5.9 msec, respectively. C, Pseudocolor surface contour plot of the field potential (left panel) and CSD (right panel) profile. The field negativity is observed first in layers V–VI from where it propagates to layers III and II. It is largest and shows the longest duration in layer III. Associated with the initial field negativities are spatially distinct current sinks lasting for ∼2 msec, seen first in layers V–VI and subsequently in layers III and II. After the initial sink there is a rhythmic reappearance of sinks in layers V–VI (approximate frequency 200 Hz), whereas a more tonic sink of elongated duration (12 msec) appears in layer III, far outlasting those in either layers V–VI or II.