(A) Schematic location of imaging sites in cortex, primary visual cortex of mouse, rat (not shown), and cat (area 18).
(B) Two-photon bulk-loaded calcium imaging in vivo. Femtosecond-pulsed laser light is used to measure calcium-induced fluorescence changes in neurons. A single plane is imaged at one time. Lower panel: example image. All cells are loaded with OGB-1 AM (green), and astrocytes are labeled with SR101 (red/yellow).
(C) Relationship between calcium concentration and spiking activity. Top: a simulated train of 5 spikes. Middle: spike rate, computed by smoothing the spike train with a Gaussian kernel. Bottom: expected somatic calcium concentration, computed by convolving an exponential describing calcium influx with the spike train.