The advantages and limitations of permanent or reversible deactivation techniques in the assessment of neural function.

This review considers the different forms of reversible deactivation and how they differ from each other and from more conventional permanent deactivation methods. The different methods of chemical and cooling reversible inactivation and the limitations of each are discussed. Finally, future directions in the quest to localize brain function in the experimental animal are considered and how this work relates to emerging non-invasive imaging techniques presently being used with humans.

The cryoloop: an adaptable reversible cooling deactivation method for behavioral or electrophysiological assessment of neural function.

We describe a very adaptable reversible inactivation technique for the behavioral or electrophysiological analysis of neural circuits. The cryoloop device can be permanently implanted or topically applied in an acute preparation to apply cold to discrete surface regions of the central nervous system (e.g. cerebral cortex or midbrain). The cryoloop consists of a custom shaped, stainless steel, hypodermic tubing and cooling is effected by passing chilled methanol through the lumen of the tubing. Cryoloop temperature is monitored by a microthermocouple attached to the union of the loop, and can be maintained within +/- 1 degrees C of a desired temperature. In chronic preparations, implanted cryoloops have been maintained in cats and monkeys for periods in excess of 2 years. After this period there are no structural, metabolic of functional changes in the deactivated tissue, and full reversibility of cooling-induced effects is maintained. Operation of multiple cryoprobes provides great flexibility of experimental protocols, permits double and triple functional dissociations to be made, and strengthens experimental design considerably.