ADJUSTMENT THE NERVOUS SYSTEM 127 



The Cerebral Cortex and Conditioned Reflexes 



We may, from the standpoint of physiology, regard the 

 responses in which the higher parts of the brain take part as a 

 particular kind of reflexes. But they are more modifiable by 

 effects influencing them by way of other parts of the nervous 

 system than the machine-like spinal reflexes are. Thus, the con- 

 tact of the hand with a hot object is always followed by with- 

 drawal of the hand, but not necessarily by the use of "strong 

 language." Here we see the intervention of inhibitory processes, 

 which play so great a part in the functions of the cerebral hemi- 

 spheres. The surface of these organs, known as the cortex, is the 

 seat of the highest intellectual activities. In the investigation of 

 its functions, a method has been developed by the eminent Russian 

 physiologist, Pavlov, in which that aspect referred to above, namely, 

 their variable nature, has been made use of in a systematic manner. 

 Although a detailed account is beyond the scope of this book (see 

 p., pp. 502-507), a brief consideration will help towards a general 

 comprehension of the mode of action of the central nervous system. 



This system has often been compared to a telephone exchange, 

 and the resemblance is in many ways a striking one. Any one 

 subscriber can be connected up with any other subscriber, just as 

 a particular muscle can be used in reflexes from many various 

 receptor organs. In this way the line to any one subscriber may 

 be regarded as analogous to the final common path in relation to 

 all other subscribers, and the costly and ineffective method of 

 having this person separately connected by a special wire to each 

 of the others is avoided. It is also possible fora subscriber to be 

 permanently connected by a separate wire to another, so that these 

 two can talk at will without having to be put into communication 

 through the central exchange. This represents that kind of reflex 

 with which we are familiar in the spinal reflex, but which is also 

 to be found in parts of the brain intervening between the spinal 

 cord and the cerebral cortex. It may be called unconditioned^ 

 because no special conditions need be present for it to be 

 manifested. But the usual method is for a subscriber only to be 

 temporarily connected with another, and the possibility of any 

 resulting conversation depends on this condition. The contrast 

 between the conditioned reflex, as it is obtained from the cerebral 

 cortex, and the unconditioned one of drawing away the hand from 

 a hot object, may be illustrated by supposing that one agrees with 

 a friend to meet at a certain place at a certain time. We 

 expect to do so under the conditions arranged. But a subsequent 

 passing by the same place is not expected to have the same result. 

 The association, as we may call it, is merely a temporary one. 



