Studies employing electrical stimulation in chronically prepared, freely moving animals have given disappointingly little information about the functions of the caudate nucleus. In those instances in which positive motor responses have been reported,1,2,7 there is still the problem of refuting or confirming Kinnier Wilson's arguments that the effects are owing to excitation of fibers of passage.19
In investigations of the limbic system, we have employed local chemical stimulation of the brain as an adjunct to electrical stimulation.13 We have favored the use of acetylcholine or related drugs because acetylcholine is a naturally occurring substance in the brain and may function in the central nervous system as a neural transmitter. The use of cholinergic stimulation for exploration of the functions of the caudate seemed particularly appropriate for several reasons. 1. Such stimulation ostensibly does not excite nerve fibers and would therefore not activate fibers of passage. 2. Similarly,