54 BRAINS OF RATS AND MEN 



thalamus (Pavlov, 1923), but in their simpler forms 

 the thalamus alone is competent, as shown by the 

 fact that such associations can readily be acquired by 

 fishes, in which the cerebral cortex is absent or very 

 rudimentary, and by invertebrates. 



Whether a rat deprived of all its cerebral cortex 

 can acquire conditioned reactions or simple sensori- 

 motor habits has not been fully investigated. It is to 

 be expected that this can be done in the case of some 

 simple acquired habits. The experiments of Lashley 

 to be described in detail in subsequent chapters show 

 that simple habits can be acquired in the absence of 

 most of the cortex, and Jellinek and Koppanyi (1923) 

 report a similar case in which all or nearly all of the 

 cortex of a rat was destroyed and simple associative 

 memory habits were subsequently acquired. 



Figure 5 illustrates the apparatus of associative 

 memory in greatly simplified form, using Pavlov's 

 conditioned salivatory reflex as an example. Stimula- 

 tion of taste buds on the tongue activates the primary 

 gustatory center through the VII nerve. This in 

 turn excites the salivatory nucleus and the submaxil- 

 lary salivary gland. This is a local reflex arc of the 

 medulla oblongata provided ready-made at birth, and 

 salivation in response to food substances in the mouth 

 is not a learned reaction. The VIII nerve passes 

 from the cochlea to the primary auditory center, from 

 which a pathway runs to the spinal cord and out to 

 the neck muscles for turning the head toward the 



