Fig. 2.

Recent VSD-based GEVIs. a Schematic drawing of two configurations of VSD-based GEVIs. Left: VSD fusion with intracellular fluorescent protein (FP). Right: VSD insertion with extracellular circularly permuted FP. b Left: Expression of FlicR1, a red-shifted indicator with flipped polarity, in dissociated hippocampal neuron. Right: optical (red) and electrical (black) responses to action potentials at 5 Hz, recorded with one-photon imaging. Modified with permission from [43]. c Left: Expression of Marina, a green indicator with flipped polarity in cultured hippocampal neurons. Right: Spontaneous spiking activity in a cortical neuron from an acute brain slice recorded with one-photon imaging. Modified from [44] with permission