This study has shown that building in a certain amount of ability with the nonpreferred hand can increase the likelihood of getting a transfer in handedness with very small lesions. The limit of lesion size may eventually be made smaller but at present it appears to be between Vz and 1 cu. mm. Even with lesions this large the results indicate that there is no critical area common for all Ss but a shifting of the region in individual Ss. Layers 5 and 6 probably contain the cells controlling handedness, but a more definitive determination requires techniques not at present available.
Acetylcholine (Ach) seems to have a facilitating effect in the preferential use of the hands when applied locally to one hemisphere of the rat's brain (2). However, the results are equivocal when all of the experimental animals are taken into consideration. Only in ambidextrous rats is the effect likely to be observed and even in such cases, negative results appear as frequently as positive. Nevertheless, localized clonic contractions of the forelimb, which are also sporadic and uncertain but which are unequivocal when they do occur, lend support to the notion that some effect is being produced.Early work indicated that some means should be sought to increase the incidence of the change. The literature is replete with suggestions of ways to stabilize Ach in animal tissues, and thus make it more effective. Inhibitors of choline esterase, buffers to maintain acidity, changes in saline concentration, solvents natural to nerve tissue, associated drugs with similar central effects; all of these are possibilities which come to mind.
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