32 BRAIN MECHANISMS AND LEARNING 



Certainly this is related to our subjective experience of free will in 

 choosing what we do and what we attend to. But before accepting un- 

 caused causes, let us recall that computers can also learn to develop a set of 

 values and to choose between programmed activities, so that we need not 

 yet despair of finding the neural mechanisms for this ultimate core of 

 higher behaviour. Given a programme or plan, a computer can rapidly 

 scan the existing situation and select that set of actions which will come 

 closest to matching an 'ideal' that has been given it. Behaviour is similarly 

 tracking; as individual or as race, organisms respond to the challenge of 

 their environment. Behaviour, as remarked earlier, is such as to bring the 

 expected future condition of the organism into congruence with the 

 desired condition. This can be done blindly, starting from the existent 

 state, or it can be done with greater or lesser foresight bv projecting the 

 existing state into its probable future condition. 



The nervous system and learning endow the animals possessing them 

 with this ability to extrapolate the curve of existence and so to act with 

 foresight. The cat jumps not to where the mouse is, but to where it may 

 be expected to be. Man not only can himself run away from the batter in 

 order to catch a flyball; he can also build into computing tracking 

 mechanisms, as anti-aircraft guns, the same ability. Man himself, with his 

 ten billion or more cortical neurones', can out-perform all other projecient 

 machines, so far built by nature or by him, in projecting further and more 

 elaborately into the future. This is possible because of a great repertoire of 

 past memories, or partially organized and interacting programmes, and of 

 complex probability computers that take account of past and present 

 factors and assign value or utile weights to them. The basic molecular, 

 cellular and organismic mechanisms involved, however, are probably not 

 much different from frog to physiologist. It is an intriguing question 

 whether equally effective ones will one day be evolved for man's machines. 



GROUP DISCUSSION 



Hebb. I would like to raise two points. One is with respect to the work or 

 McConnell on the flatworm which I found extremely puzzling. I do not know 

 whether it can be compared to learning in mammals. If this type of mechanism 

 applied in the mammal, presumably Sperrv's work should not have given the result 

 it did by just cutting the corpus callosum. We must be dealing with a different 

 phenomenon, when we talk of learning in the mammals, from the phenomenon 

 that McConnell studied. Secondly, with respect to the effects of anaesthetics on the 

 consolidation period of learning, I would like to cite some work by Muriel Stern, 

 concerning the effect of barbiturates on learning. The effect you observed may be a 

 general disturbance, rather than a specific interference with the retention period. 

 The effect of barbiturates is that of depressing learning capacity for a period of some 



