We propose a two-photon microscope scheme capable of real-time, three-dimensional investigation of the electric activity pattern of neural networks or signal summation rules of individual neurons in a 0.6 mm x 0.6 mm x 0.2 mm volume of the sample. The points of measurement are chosen according to a conventional scanning two-photon image, and they are addressed by separately adjustable optical fibers. This allows scanning at kilohertz repetition rates of as many as 100 data points. Submicrometer spatial resolution is maintained during the measurement similarly to conventional two-photon microscopy.