DIFFERENCES IN THE RECOVERY RATE OF A LEARNED FORELIMB MOVEMENT AFTERABLATION OF THE MOTOR CORTEX IN RIGHT AND LEFT-HEMISPHERE IN WHITE-RATS

After ablation of the motor cortex contralateral to the preferred limb , rats were forced to use this limb in grasping food out of a horizont al tube by restraining the non-preferred foreleg with a bracelet. In a right-handed rat the motor behaviour is less impaired and the recover y is better after a left hemisphere lesion in comparison with a left-h anded rat after a right hemisphere lesion. This difference is primaril y the time needed to use the limb in reaching for seed (testperiod 3) and the total time needed for 10 successive seizings of seed (testperi od 5). Surprisingly, the differences in the course of recovery do not correlate with the degree of preoperative limb preference: the initial ly ambidextrous rate also show the same differences in results of the motor cortex ablation in left and right hemisphere. However, in the gr oup of initially consistent ambidextrous rats, after 10 weeks of tests with a restrained forelimb, the testing under unrestrained free condi tions shows a gradual decrease in the induced limb preference and a sh ift to the use of the foreleg contralateral to the intact hemisphere, while in contrast the initially consistent left- or right-handed rats preserve the limb preference under the unrestrained testing conditions . Therefore the degree of initial preference still influences the choi ce of limb after motor cortex ablation and intensive training to use t he 'damaged' limb.