Comments concerning the Basis of Learning Enhancement with Central Nervous System Stimulants
T h e results of a number of investigations have shown that, in rats, rate of learning is facilitated by low doses of several central nervous system stimulants. In an early study, Lashley ( 8 ) reported that maze learning was facilitated by strychnine sulphate. Recently, this finding was successfully replicated by us (14). In other studies, pre-trial injections of strychnine have been found to facilitate the performance of several problems, including maze learning ( 12, 1 8 ) , escape and avoidance learning ( 7 ) , successive discrimination learning ( 2 1 ) , simultaneous discrimination learning ( 15 ) , and a delayed alternation response ( 1 3 ) . Facilitation of maze learning and escape and avoidance learning has also been obtained with the strychnine-like compound 5-7-diphenyl-1-3-diazadamantan-6-01 (1757 I.S.) (7 , 1 6 ) . O n the basis of these findings, we have suggesced in several papers that these compounds facilitate learning by potentiating the consolidation of the neural processes mediating learning. The consolidation interpretation has been discussed in several of the papers cited but was not proposed in our 1959 paper ( 1 4 ) as suggested by Thiessen et al., ( 2 4 ) who also cited the paper incorrectly. O n the assumption chat these hypothesized consolidation processes continue for some time following training ( 3, 1 9 ) , a subsequent series of studies investigated the effects, on learning, of injections of s t im~~lan ts administered after learning trials (with one trial given each day) . Evidence for facilitation of learning using this latter procedure has been obtained with strychnine ( I S ) , 1757 I.S. (6, 1 7 ) and picrotoxin ( 1 ) . In these experiments the animals were always tested over 23 hr. after each injection and were thus never tested while under the immediate influence of the drugs. These findings provide additional support for the interpretation that the enhanced learning produced by these compounds is due to a facilitation of post-trial neura; consolidation. In a recent article Tliliessen, Schlesinger, and Calhoun ( 2 4 ) have questioned our interpretation of these findings on both theoretical and empirical grounds and have suggested an alternative interpretation of the data. In the present paper we wish to point out that: ( a ) the criticism by Thiessen, et al. is invalid; ( b ) their alternative interpretation is unsupported by available data;