DESIGN FOR A BRAIN 1/8 



relevance or meaning. Again, a maze-rat that has learned suc- 

 cessfully has learned to produce a particular pattern of move- 

 ment; yet the learning has involved neurons which are firmly 

 supported in a close mesh of glial fibres and never move in their 

 lives. 



Finally, consider an engine-driver who has just seen a signal 

 and whose hand is on the throttle. If the light is red, the excita- 

 tion from the retina must be transmitted through the nervous 

 system so that the cells in the motor cortex send impulses down 

 to those muscles whose activity makes the throttle close. If the 

 light is green, the excitation from the retina must be transmitted 

 through the nervous system so that the cells in the motor cortex 

 make the throttle open. And the transmission is to be handled, 

 and the safety of the train guaranteed, by neurons which can 

 form no conception of ' red ', ' green ', ' train ', ' signal ', or 

 'accident ' ! Yet the system works. 



Clearly, ' normality ' at the neuronic level is inadequate to 

 ensure normality in the behaviour of the whole organism, for the 

 two forms of normality stand in no definite relationship. 



1/8. In the case of the engine-driver, it may be that there is- a 

 simple mechanism such that a red light activates a chain of nerve- 

 cells leading to the muscles which close the throttle while a green 

 light activates another chain of nerve-cells leading to the muscles 

 which make it open. In this way the effect of the colour of the 

 signal would be transmitted through the nervous system in the 

 appropriate way. 



The simplicity of the arrangement is due to the fact that we 

 are supposing that the two reactions are using two independent 

 mechanisms. This separation may well occur in the simpler 

 reactions, but it is insufficient to explain the events of the more 

 complex reactions. In most cases the ' correct ' and the ' incor- 

 rect ' neural activities are alike composed of excitations, of 

 inhibitions, and of other processes each of which is physiological 

 in itself, but whose correctness is determined not by the process 

 itself but by the relations which it bears to other processes. 



This dependence of the ' correctness ' of what is happening at 

 one point in the nervous system on what is happening at other 

 points would be shown if the engine-driver were to move over to 

 the other side of the cab. For if previously a flexion of the elbow 



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