Abstract
The study has been made on the motor activity in neuro-muscular unit (NMU) at the stage of acquiring the defensive conditioned reflex in dog.The defensive conditioned reflex in the hind limb of the dog was establishedwith the combination of unconditioned stimulus (electric shock) and conditioned stimulus (sound) which preceded by 0.5 sec. the electric shock. Afterconditioning, the differentiation was reinforced by combining the positiveconditioned stimulus and the negative one. In each situation of the conditioning, NMU discharges of M. biceps femoris were recorded and τ-S relationswere examined.
The following results were obtained:
1. Before conditioning, the many plots appeared around the curve T ratherthan the curve K on the τ-S table. This fact indicates that the hind limbmuscles of dog were suited for antigrave and tonic activities.
2. When conditioning was established, few plots appeared around the Tcurve as compared with the control, while the ones situated around the Kcurve increased in number.
3. Many points around the curve T appeared after differentiation, converselythe ones plotted around the curve K decreased. Separation of K-T curvewere also seen in this time.
n discussing the central neuro-mechanism of conditioned reflex referringto the electromyographical study of NMU, it was presumed that the cor-ticalization appears at the time when the conditioned reflex was established, and that the spinalization occurs after the differentiation was formed.
