66 BRAINS OF RATS AND MEN 



for the simpler conditioned responses, as will appear in our 

 account of the association centers of the cortex. 



Again Lashley says, "We may have to seek for changes in the 

 refractory period rather than at the synapse as the basis of the 

 learning process and for changes in the periodicity of discharge 

 within a syncytium rather than for anatomically defined conduc- 

 tion paths to account for new integrations." But it must be kept 

 in mind that anatomically defined conduction paths are present 

 and are certainly employed throughout most, if not all, of the 

 way traversed by the nervous impulses involved in conditioned 

 reflexes. An appeal to a syncytium in the correlation center where 

 the transfers effected in learning are actually made leaves us in 

 worse state than before, for this involves the total disregard of 

 the most valuable anatomical and experimental evidence now at 

 our disposal for elucidating the mechanism of correlation.^ 



As I have elsewhere pointed out (1924, pp. 103, 114, 255, 

 258, 266), non-synaptic or syncytial nervous systems lack the 

 machinery necessary for that plasticity and rapid reorganization 

 of the stable elements of a complex action system requisite for 

 facility in learning. And the experimental evidence relating to 

 periodicity of nervous discharge and alterations of refractory 

 period suggests that many of these phenomena center about the 

 synaptic junctions, whose peculiar biophysical and biochemical 

 properties are essential conditions for the manifestation of some 

 of these phenomena (Lillie, 1923, p. 272). 



Our conclusion is that, though adequate experimental proof 

 of the theoretic parts of current expositions of the nervous appa- 



^ Professor Lashley in a personal communication indicates that in 

 his use of the term "syncytium" he did not intend to stress the most dis- 

 tinctive characteristics of the non-synaptic nerve net which this word 

 usually suggests in current discussions — an important point to bear in 

 mind in reading his text. He says, "I had in mind irradiation or diffusion 

 as the outstanding property of the syncytium but did not mean to deny 

 synaptic structure or one-way conduction in the cortex." 



