STUDIES OF CEREBRAL FUNCTION IN LEARNING 281 



Langelaan [9] and of their relation to decerebrate rigidity [Wilson, 

 19], suggest a possible explanation for the results of destruction of the 

 cerebral motor structures in the rat. The initiation of almost any new 

 activity demands a modification of postural tone, the assumption of a 

 different pattern of tonic contractions, which may then persist almost 

 unaltered for some time during the performance of finer manipulative 

 movements. The behaviour of the operated rats suggests strongly that 

 their chief difficulty is in taking a new posture. Once an activity has 

 been initiated and maintained for a moment even artificially, as when 

 the animal is held in contact with the food, it may persist for a rela- 

 tively long time until some stimulus to a new posture occurs. The 

 disturbances seem most pronounced in the attempts to perform those 

 activities which require the most complex and unusual postural co- 

 ordinations : scratching and feeding. The compensations for the motor 

 disturbances also suggest that the latter involve less complex, more 

 nearly reflex, integrations than habitual acts. The primary compensa- 

 tions are not by the direct restitution of motor control (recovery from 

 the paresis) but by the acquisition of new patterns of co-ordination 

 which tend to counteract the motor difficulty, much as a normal animal 

 would adapt to a heavy weight attached to one leg. After the destruc- 

 tion of the stimulable cortex the complex adaptive mechanisms are 

 still intact. 



These facts argue strongly for a relative independence of the cerebral 

 mechanisms for control of postural activity from those for voluntary 

 movements. The hypothesis which seems best to fit the facts for the 

 rat is that the stimulable area and caudate nucleus are concerned chiefly 

 with the regulation of postural reflexes and that upon these are super- 

 imposed the more complex integrations constituting voluntary acts, 

 transmitted to the final common paths by extrapyramidal fibres. This 

 would make the cerebral motor structures an additional stage in the 

 hierarchy of spinal, vestibular, and cerebellar mechanisms for the con- 

 trol of postural reflexes. Such a function has already been ascribed to 

 the corpus striatum by Wilson [18], on the basis of work with monkeys, 

 and the present experiments add to his conclusions only the fact that 

 the stimulable area of the rat is to be classed in function with the 

 striate nucleus rather than with the cerebral habit-mechanisms. 



The Function of the Stimulable Cortex in Higher INI vmmai.s. 

 Is such a view of the function of the electro-stimulable cortex con- 

 tradicted by evidence from the study of higher animals? It is certainly 



