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BRAIN MECHANISMS AND LEARNING 



by adrenocortical hormones, it cannot be denied that the endocrine action 

 is brought about by the inhibition of a specific temporary connection, 

 which does not affect the whole series of conditioned reflex connections 

 concerned in the shaping of behaviour. Effects of a similar character may 

 be mentioned in connection with the action of sexual steroids, however, at 

 a different level. 



We should now like to pass on to some observations which show the 

 influence of the environment on the development of conditioned reflex 



Fig. 10 

 Structural relationships between forniatio reticularis, hypothalamus, septum, 

 archicortcx and pyriform area. Thick solid line shows the direct activating 

 mechanism, thin lines correspond to the modifying pathways and dotted lines 

 show the inhibitory pathways. 



connections. In recent years we have been studying in conditioned reflex 

 experiments the effect of the stimulation of the reticular formation of the 

 tegmentum on alimentary conditioned reflex activity elaborated pre- 

 viously in the normal and the neurotic states. Experiments on dogs showed 

 that stimulation of the reticular formation, more precisely of the grey 

 matter round the aqueduct of Sylvius, induced a conditioned reflex, even 

 though no positive sound stimulus was applied. This phenomenon 

 resembles a finding by Grastyan and his co-workers (1956, 1959) at our 



