Apparatus and methods for cooling and/or heating selected regions within a body are described herein. An implantable system is used to cool or heat nerve bodies down to about 15.degree. C. to diminish nerve impulses. In one embodiment, the system can include an implantable unit containing a pumping mechanism and/or various control electronics. The system has a cooling element. The cooling element can be a Peltier junction or a catheter through which hot or cold fluid flows. The heated portion of the Peltier junction can be cooled by a liquid heat transfer medium which absorbs the heat from the junction and dissipates the heat elsewhere.