We have developed a compact and lightweight microfluidic cooling device to reversibly deactivate one or more areas of the neocortex to examine its functional macrocircuitry as well as behavioral and cortical plasticity. The device, which we term the "cooling chip," consists of thin silicone tubing (through which chilled ethanol is circulated) embedded in mechanically compliant polydimethylsiloxane (PDMS). PDMS is tailored to compact device dimensions (as small as 21 mm(3)) that precisely accommodate the geometry of the targeted cortical area. The biocompatible design makes it suitable for both acute preparations and chronic implantation for long-term behavioral studies. The cooling chip accommodates an in-cortex microthermocouple measuring local cortical temperature. A microelectrode may be used to record simultaneous neural responses at the same location. Cortex temperature is controlled by computer regulation of the coolant flow, which can achieve a localized cortical temperature drop from 37 to 20°C in less than 3 min and maintain target temperature to within ±0.3°C indefinitely. Here we describe cooling chip fabrication and performance in mediating cessation of neural signaling in acute preparations of rodents, ferrets, and primates.