Single photon kilohertz frame rate imaging of neural activity

Establishing the biological basis of cognition and its disorders will require high precision spatiotemporal measurements of neural activity. Recently developed genetically encoded voltage indicators (GEVIs) report both spiking and subthreshold activity of identified neurons. However, maximally capitalising on the potential of GEVIs will require imaging at millisecond time scales, which remains challenging with standard camera systems. Here we report application of single photon avalanche diode (SPAD) sensors to imaging neural activity at kilohertz frame rates. SPADs are electronic devices that when activated by a single photon cause an avalanche of electrons and a large electric current. We use an array of SPAD sensors to image individual neurons expressing the GEVI Voltron-JF525-HTL. We show that subthreshold and spiking activity can be resolved with shot noise limited signals at frame rates of up to 10 kHz. SPAD imaging was able to reveal millisecond scale synchronisation of neural activity in an ex-vivo seizure model. SPAD sensors may have widespread applications for investigation of millisecond timescale neural dynamics. Note. This worked was funded by: 1. Wellcome Trust (ISSF3 award IS3-R2.36 to IG and MFN, and Investigator Award 200855/Z/16/Z to MFN); 2. BBSRC EastBio doctoral training programme; 3. EPSRC (EP/S001638/1).