ORIGIN AND SIGNIFICANCE OF THE CEREBRAL CORTEX 235 



sory stimulation directly from the periphery. The effect of 

 this arrangement is that the central motor path during function 

 is under the influence of sensory stimulation at both ends, and 

 is not, as commonly described, under simple sensory stimula- 

 tion at the cortical end and purely emissive in function at the 

 spinal end. 



Viewed from the standpoint of cerebral dynamics, the exact 

 physiological effect of the discharge of a central motor bundle 

 such as the pyramidal tract will be dependent upon the com- 

 bined action of the sensory stimulation at the cortical end and 

 the state of sensory excitation at the spinal end, as well as 

 upon the resistance of the motor apparatus itself. 



We saw in a previous paragraph how the simple reflexes of 

 the spinal cord may become factors in the stimulus complex 

 of the cortex. Here we find, conversely, that the efferent cor- 

 tical discharge may become a factor in the local reflex stimula- 

 tion of a motor spinal neurone. From both standpoints, Dewey's 

 conception of the unitary nature of the organic circuit, as con- 

 trasted with the classical reflex arc concept, receives strong 

 support. 



The thalamic association centers probably serve as the organs 

 par excellence where are elaborated those organic circuits which 

 give to the higher apperceptive processes of the cortex that 

 quale to which Dewey refers. The origin of this quale is to be 

 sought partly in the subcortical assimilation of a present stim- 

 ulus complex to the pre-existing organic circuits structurally 

 laid down in the reflex mechanism, and partly in an affective 

 quality pertaining to the several organic circuits involved in 

 the reaction. This affective quality may be innate or it may 

 have been acquired by experience of the results of previous 

 reactions of the sort in question. 



Head and Holmes 5 have brought forward some very inter- 

 esting evidence that not only the affective quale of sensations, 

 but also the emotional life in general, is functionally related to 

 the primitive intrinsic nuclei of the thalamus, rather than to 

 cortical activity. And certainly there is much evidence in the 

 behavior of lower animals, especially birds, that a high degree 

 of emotional activity is possible where the basal centers are 



5 Brain, vol. 34, p. 255, 1911. 



