3t8 



BRAIN MECHANISMS AND LEARNING 



necessary to complement the notion of synapse with a wider knowledge of 

 interneuronal relations. A more adequate basic notion of synapse should 

 not exclude any kind o{ close contact between two Diemhraiies, of which at h'ast 

 one is of a nervons nature. If this dctmition is accepted, different types of 

 synapses can be described: their distinction into synaptic and non-synaptic 

 contacts would be a matter of words rather than of facts. 



If we remember that the physiological concept of synapse was worked 

 out with a partial knowledge of the functional contacts between neurones, 



Fig. 9 

 Axo-dcndritic cross contact in cerebellum (I). Photomicrograph ot the cerebellum of cat. 

 A.d. syn. shows a typical cross contact between a parallel fibre (horizontal in figure) and a 

 dendrite of a Purkinjc cell (vertical in figure) (see also Figs. lo and ii). (Golgi chromo-argent 

 c methods. Cajal's variance.) 



we shall be more willing to admit, within the general theory of synaptic 

 function, the existence of interneuronal influences which form a comple- 

 ment to, and do not contradict, the law of dynamic polarization, and we 

 shall be even more willing to admit that the law of insulated conduction 

 is complemented by a conduction which is neither insulated nor massive. 

 What the fundamental functional differences between neuronal sub- 

 structures are is not known. Neither structures nor substructures, similar 

 in all neurones, can account for notable physiological differences. The 

 synaptic spectruni (afferent and efferent connections of one neurone) allows 



