ADJUSTMENT THE NERVOUS SYSTEM 129 



sound, but two minutes afterwards, the process being repeated until 

 the conditioned reflex is duly formed. We then find that the 

 sound of the bell is not followed immediately by secretion of saliva, 

 but only after two minutes have elapsed. It is obvious that some- 

 thing in the nature of an inhibition must have been going on 

 during these two minutes. That this is the case can be shown by 

 the application of a stimulus in this interval, the stimulus being 

 one that does not produce secretion of itself, but has an inhibiting 

 action on other stimuli, such as the flash of light above mentioned. 

 The effect of this indifferent stimulus in the interval of two minutes 

 before the secretion normally appears is to cause the appearance of 

 saliva at once. The previous inhibition is itself inhibited, so that 

 a positive result shows itself. 



The inhibitory influences are spread over a wide area of the 

 cortex ; in fact, during a conditioned reflex it appears that practi- 

 cally the whole of the cortex, with the exception of the part 

 concerned, is in a state of inhibition. 



We may conclude with one more example. Suppose that a 

 sound and a light are made, each for itself, signals for secretion, 

 but that when both are presented together no food is given, so 

 that the reflex to the two stimuli together becomes one for no 

 secretion, and one stimulus must inhibit the other. If one of these 

 be afterwards presented alone, secretion follows, and if, while the 

 secretion is in progress, the other, also active by itself alone, be 

 superadded, the secretion stops. 



It will be seen that we have in these new associations the 

 physiological basis of memory and of the formation of habits, 

 together with the possibility of their loss by breaking of the con- 

 nections. 



The fact must not be passed over that we have in the cortex 

 certain areas whose artificial stimulation causes definite move- 

 ments. These are called motor areas, but it must not be supposed 

 that they are of the same nature as the motor neurones of the final 

 common path. They may rather be looked upon as the physio- 

 logical representatives of the ideas of particular movements, 

 although their activity is not necessarily associated with conscious- 

 ness, since the phenomena are shown in the anaesthetised animal. 



The results of artificial stimulation of such cortical areas show 

 the complexity of the various effects produced at different times by 

 stimulation of one and the same point. Thus, after rest a point 

 usually gives contraction of the muscle in the same way as it had 

 previously, but if it be stimulated immediately after a previous 

 response, inhibition of the muscle occurs. If a point which normally 

 gives extension of the elbow be stimulated immediately after that 

 of another point which gives flexion, the former point gives flexion 



