Fig. 4

Optical mapping of the BIT. a The map of the excitation spread for the evoked (first) optical action potentials (shown in Fig. 3). Open triangle with Stim Position of the stimulation. b Map of the excitation spread for the second optical action potentials (shown in Fig. 3). Open circle with F Position of the anomalous focus where the second action potential first appeared. c, d Maps of the excitation spread for the second optical action potential of two other events of BIT. The positions of the wavefronts are displayed as isochrone curves at 20-ms intervals. Peripheral gray areas Areas where the delay could not be measured due to the absence of the signals or the preparation