Figure 2. Ca²⁺ network imaging of failure of ictal propagation in mouse cortical slices.

(a) Mean neuronal Ca²⁺ fluorescence (centre-surround subtraction10) from 65 cells during three different epochs (epochs defined from concurrent voltage clamp recording of a layer 5 pyramidal cell within the field of view; all imaged cells within 200 μm of the recorded cell). Epoch 1 was a period of ictal activity elsewhere in the slice, which failed to invade the local territory. Epoch was baseline activity, and epoch 3 shows a full ictal event that did recruit the field of view. The grey shaded area shows the upper and lower extent of 5 s.e.m. signal for the 65 cells. Note: how even during the 'Failure of propagation', the mean signal comfortably exceeds baseline (mean±5× s.e.m.). (b) Brain slice loaded with OGB1. Two movies of this slice are in the Supplementary Information, showing a full ictal event and another event that failed to propagate into this territory. Representative traces of neuronal activity for these two events are shown in c and d, together with a voltage clamp recording of a local pyramidal cell (V_hold=−30 mV). In the V_clamp recording, note the upward deflections (predominant inhibition) for the failure, and the downward deflections for the successful propagation, as shown also in the example in panel a. (e) Coherence matrix for the Ca²⁺ signal of 65 imaged neurons, showing a general lack of coherence when the ictal event fails to invade, in contrast with the highly coherent signal when the ictal event does invade (number of coherence measures=2080; non-participation coherence (mean±s.d.)=0.494±0.172; post-recruitment coherence=0.914±0.075; t_s=102.0; P<<0.001, Student's t-test). (f) Line scan of a propagating ictal wavefront, derived from ×10 magnification Ca²⁺ network imaging. Spatial profiles of the wavefront (dotted line) were derived during periods of stability. (g) The spatial profile of activity measured in eight brain slices.