Mapping neuronal activity by imaging intrinsic optical signals

The ability to map activity patterns in large groups of neurons over large areas is critical for understanding network behavior. Imaging of intrinsic optical signals provides a unique insight into the group behavior of neurons that is not replicated by conventional electrophysiological recordings or voltage-sensitive dyes. Intrinsic optical signals are changes in the optical properties of tissue, such as light scattering, absorption, or transmittance, that can be detected using imaging techniques. Several types of intrinsic optical signals can be detected in neuronal tissue and different cellular phenomena underlie them. This review describes some of the uses of this technique and what is known about the underlying cellular mechanisms.