Innate versus learned factors determining limb preference in the rat.

The basic factors determining forelimb preference in the performance of different skilled movements were studied in white rats. To analyse whether limb preference actually reflects an initial individual motor asymmetry or is a result of instrumental learning (the first successful movement becoming fixed), the method of retrograde amnesia from electroconvulsive shock was used. It was shown that limb preference is initial and not a results of learning and, evidently, is due to intrinsic factors. The preferred limb can be identified in as few as 3 successful movements. There is a gradation among animals according to the degree of initial limb preference and its resistance to rearrangement of the motor task. The differences of limb preference in different movements were also analysed. Dependence of the preference on the character of the required movement was shown. Four basic types of movement were revealed by factor analysis. As different muscular groups (distal and proximal), controlled by different descending motor systems can be involved in the performance of different movements, it is assumed that the initial motor asymmetry in each movement is a result of asymmetry of central motor structures involved in the realization of the movement. In the same animal asymmetry of different motor structures might be different. This could explain different limb preference in different movements.