Optical imaging combined with targeted electrical recordings, microstimulation, or tracer injections.

To facilitate the combination of optical imaging with various electrode-based techniques, we have designed and produced a skull-mounting "sliding-top cranial window" and a removable "electrode positioner microdrive". These new devices were used to study sensory processing in chronic and acute experiments in the cerebral cortices of cats and monkeys. This assembly allows simultaneous optical imaging of intrinsic signals or voltage-sensitive dyes combined with extracellular recording (single and multiple unit recording and local field potential), intracellular recording, microstimulation, or targeted injection of tracers. After the functional architecture is determined by optical imaging, electrodes are targeted into a selected cortical site under full visual control, at a variety of penetration angles (30-90 degrees ), accessing a large cortical area. The device consists of three parts: (1) a skull-mounting chamber, (2) a sliding cap, and (3) a microdrive. The microdrive can easily be removed and the cranial window is then sealed and covered with a flat protective cover. For chronic experiments, this arrangement allows the animal to be handled over a long period while fitted with a sealed cranial window of minimal volume and weight, and with negligible risk of accidental damage or infection.