D. O. HEBB 47 



always thought that it is a very good idea that rcvcrberatory circuit activity gives 

 the basis for tormation of memory traces. 



Hebb. As Dr Eccles has picked me as a target, I would say that, in my opinion, 

 the notion that transmission is solely chemical is pure dogma. That is to say, I 

 think that Dr Eccles has provided convincing and powerful evidence that the 

 primary transmission is chemical. However I can't see what evidence possibly 

 could rule out an electrical current flow as an ancillary or supporting mechanism 

 of synaptic transmission. 



The second point is that I would agree entirely, and I take it that I^r Gerard docs 

 also, that one trial means one presentation of the stimulus, but it doesn't mean one 

 burst of impulses. Of course I don't suppose that 'one trial learning' means that 

 only one impulse passes the synapse, and does the trick. But further I would point 

 out that in this experiment of course we are dealing with cumulative effects 

 because we have no direct evidence of learning after one presentation oi the 

 digits. 



Gerard. First, I think it is unfortunate that l^r Hebb has jumped three levels: 

 from total behaviour, to organ, to cell, organelle or molecule. This is just too far a 

 jump at any one time to be profitable theoretically. I think it unfortunate that he 

 contaminated some very precise and provoking issues by bringing in the synaptic 

 endings, which are irrelevant at this point. I don't think the argument that is 

 brewing, as to whether the synaptic change is electrical or chemical, or whatever, is 

 really relevant to the particular problem raised. It is relevant to all kinds of 

 problems but too diffuse to matter for this one. 



Second, I raise the question whether you really are dealing in your experiments 

 with a structural memory, in contrast to a dynamic one. It seems to me you have 

 something very similar to what happens when I look up a telephone number in the 

 phone-book, keep it in my mind for a bit, make the call and immediately forget 

 the number so completely that if something goes wrong, and I must dial again, I 

 must look it up again. This is perhaps related to the point that Dr Eccles was making 

 about keeping the memory going; and the psychologists here are certainly aware 

 ot Broadbent's work on the temporary storage of information before passing it 

 into a permanent storage as a lasting memor\-, whatever the neurological mechan- 

 isms there may be. 



Third, I completely agree with the point that Dr Hebb makes about what we 

 might call 'imput overload', and the fact that the more elaborate nervous systems 

 often tangle themselves up in their own sophistication. Let me remind you of two 

 experiments. Some of the original work of Bavelas, following Kurt Lewin, 

 involved five people in a certain communication network. Each started with part 

 of the answer to a problem, such as what the colours of certain marbles are; and by 

 communicating in the intervals each had to get the total information. This they did 

 very easily when the marbles were solid colours; but, having worked with a pattern 

 problem, they could not solve the solid colour problem because their attention 

 focused on minute flaws in the colour. This kind of knowing too much was proved 

 at another level, of disease dia2;nosis. Skilled clinicians diagnosed trom a history less 

 correctly than did clerks given certain key items to look for. 



So I am not surprised that monkeys may learn certain simple problems with 

 greater difficulty than rats, and perhaps man with even greater difficulty than 

 monkeys. But it is going much too far from that to say that learning has nothing 



