FIGURE 1.

Low-voltage fast ictal discharges can occur spontaneously or be triggered by optogenetic activation of parvalbumin-positive interneurons. (A) Spontaneous ictal discharges occurring during bath application of 4-aminopyridine (4AP); 1 of the events is further expanded to show the onset pattern (asterisks). (B) Ictal discharges evoked by 1-second light pulses during bath application of 4AP; 1 of the events is further expanded to compare the onset patterns (asterisks). Note that in both A and B, the ictal discharge is preceded by a negative-going interictal field potential (arrows). (C) Changes induced by concomitant bath application of picrotoxin and CGP55845 on the ictal discharge evoked by a train of 1-second light pulses (4AP, 150μM panel). Note that under control conditions, the first light pulse induces a positive-going monospike (expanded example) that is followed by ictal synchronization, whereas during γ-aminobutyric acid (GABA)_A and GABA_B receptor antagonism both ictal discharge and the ability of light pulses to drive interictal events are abolished. Under these conditions, negative-going polyspikes (expanded example) occur regardless of the light pulses for at least 20 minutes (maximum time recorded); note the different vertical scales in the expanded examples.