Conditioned Motor Reflexes Research Articles

Myotonia Congenita in the Goat

In the course of conditioned motor reflex experiments on goats, we had the opportunity of observing so-called “stiff-legged” goats. Four such animals were furnished us through the kindness of Mr. D. E. Motlow, of Lynchburg, Tennessee.It has been noted for years that animals of this strain, when startled, stiffen and fall over, remaining immobile for some seconds in what at first appears to be a general tonic spasm. Accordingly, they have commonly been labelled “nervous,” “stiff-legged” or “epileptoid” goats.Our investigations show, however, that this seizure is not a general tonic spasm produced by a special type of stimulus, but is caused by the failure of individual muscles to relax normally when strongly stimulated after a period of rest.Stimulation of the motor points of the thigh with an adequate faradic current produces, not a simple twitch, but a tetanic contraction of the individual muscle or muscle group, with relaxation in from 5 to 30 seconds. On successive stimulation, the period of relaxation...

Auditory Conditioned Reflexes in the Thyroidectomized Sheep and Goat.

The lethargy of the cretin sheep or goat, and its apparent indifference to its environment, suggest a fundamental defect in cerebral function, but when the animal is subjected to simple learning tests the deviation from the normal, under experimental conditions, is less striking. For example, the animal, unless it is suffering one of its recurrent periods of prostration, learns the maze with a single cul de sac as well as the control. It is only when the blind alley is reversed in position, at every trial, that striking deviations from normal behavior appear. The extreme complexity of the animal's response in the labyrinth makes the analysis of the data in physiological terms very difficult. For this reason the maze studies have been abandoned in favor of the conditioned motor reflex method. A systematic investigation of cerebral activity involves, according to Pavlov, two problems, a study of the analyzers (receptors with their central terminations) and of the mechanism for the formation of temporary nervous connections. In a preliminary study it was demonstrated that the formation of a simple tactile conditioned reflex was effected as easily in the cretin as in the normal sheep. Secondary conditioned reflexes of proprioceptive origin added to the primary tactile reflex were observed in both operated and control animals. Since the alternating maze problem exhibited marked differences between cretin and normal, which were shown neither in the simple maze nor in the formation of the simple conditioned reflex, it was decided to attempt to form more difficult conditioned reflexes, viz., discriminative and delayed reflexes to the sound of the metronome.

A Laboratory for the Study of Conditioned Motor Reflexes

A Laboratory for the Study of Conditioned Motor Reflexes

A preliminary study of conditioned motor reflexes in thyroidectomized sheep.

The investigation of habit formation in thyroidectomized sheep and goats by the maze method has yielded results difficult to analyze because of the complicated responses elicited. The conditioned motor reflex method of Bekhterev has, therefore, been adopted. In a preliminary experiment a conditioned reflex to a tactile stimulus was established in three animals, two thyroidectomized sheep, aged three and four years respectively, and the twin control of the three year cretin. Tactile stimuli were applied to a spot on the rump, at the rate of thirty per minute, for periods varying from two to ten seconds. With the final stimulus, a far-adic current was applied to the left foreleg of sufficient intensity to evoke a defensive movement. The first definite leg movement, in response to the tactile stimulus alone, occurred at the tenth combination in the control and in the three year cretin, and at the seventeenth combination in the older cretin. At the end of the ninth day and forty-fifth combination, one milligram of thyroxin was administered to each thyroidectomized animal. In spite of this, one and one half months later the younger cretin died and the training of the other animals was then discontinued, after two hundred thirty-eight combinations of conditioned and unconditioned stimuli. After an interval of six and one half months the tactile stimulus without reenforcement evoked a vigorous conditioned reflex in both normal and cretin sheep. This is shown in Fig. 1, the tracing from the cretin appearing at the left. Continued tactile stimulation without application of the faradic current soon elicited a less extensive response (see Fig. 2) and finally, after one hundred nine periods of stimulation, distributed over sixteen days, the conditioned reflex failed to appear in either animal on the seventeenth day.