Spinal conduction and kinesthetic sensitivity in the maze habit.

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Abstract
The important place given to kinesthetic and organic sensations in recent psychological theory is pointed out, and the tendency to argue for the immediate completion of the conditioned-reflex circuit in motor activity and to substitute the conception of chain reflexes for that of continued intraneural activity. The problem of this investigation is to find whether the maze habit is controlled by kinesthetic sensitivity or by some wholly intraneural mechanism, once the habit has been learned. The method was to train albino rats in a simple maze, destroy certain afferent tracts in the cord, then test the effect of this upon the known ability in maze running. The lesions in the cord included the pyramidal tract, the fasciculus gracilis, the fasciculus cuneatus, the dorsal, ventral and lateral funiculi. A surprising result was that the rats retained the ability to orient in the maze after destruction of the pyramidal tract. It is concluded from this that maze running is not restricted to any definite tract, but that the impulses descend either diffusely or over alternate tracts in the different funiculi. The evidence indicates that no particular afferent path of the cervical cord is essential for the performance of the maze habit. Possibility of a shift to other sensory cues such as olfactory, auditory, or visual was carefully controlled; also the possibility of using proprioceptive cues from the muscles of the neck and vestibule. That afferent impulses ascended by some part of the cord which happened to remain intact was considered impossible because of the definite nature of the localization of the afferent conduction paths. The conclusions are (1) that the engram of the maze habit consists of some central organization in which the general direction and succession of turns in the maze are so recorded that once the series is initiated the essential sequence of movements may be performed in the absence of sensory control and with considerable variation in the movements involved, (2) that the theory of chain reflex arcs demanding a continuity of adequate stimuli and constancy of motor response is not adequate to explain the observed facts.

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