A pressure system for the microinjection of substances into the brain of awake monkeys

We describe a method for placing pressure microinjections of drugs or anatomical tracers in physiologically defined sites in the brain of awake monkeys. This method provides a means to record neuronal activity from the tip of an injection cannula so that an injection can be made at a physiologically defined location. It uses pressure in a closed system to precisely control the amount of fluid injected and provides a visible means for monitoring injection volume. The injection cannula is easy to make with readily available components and can be used repeatedly for multiple recording sessions and injections.