Summary and Ge?ieral Discussion 369 



formance deterioration, while in the annnals in which these changes 

 were present during learning, performance continues perfectly. 

 Certain chemical changes seem to facilitate learning, while others 

 slow it. These groups showed differential sensitivity to drugs many 

 months after training, indicating that the effects of the small elec- 

 trolyte shifts are long lasting. These various findings show that 

 very small local electrolyte shifts seem capable of affecting the 

 long-term storage of an experience in such a way that readout 

 is optimal when the electrolyte microenvironment of the readout 

 mechanism resembles the situation during the initial experience. 



I would like to add just one thing. We have replicated the 

 cannibalism experiments of McConnell using a blind procedure. 

 It seems to me that the most striking evidence in favor of a sequence 

 specificity model comes from such studies. 



Gerard: Let me answer your second question about the aza- 

 guanine findings first. That paper appeared while our own experi- 

 ments were in progress and were coming out the same way. As 

 to your rounded-up planaria, I seem to remember that Child and 

 Hyman got smaller segments to regenerate, but this is an unim- 

 portant detail. I am not quite sure what you are asking of me. 

 Maybe another question will help: When the cells reorganize 

 inside such a sheath or coating and are all mixed up, if you have 

 previously trained them, do they remember? 



John: That is one reason why we are doing tissue culture ex- 

 periments. I do not know yet. 



Gerard: Regarding your electrolyte shift, this strikes me as 

 exactly what would be expected, on the following argument. 

 Small shifts in the calcium-potassium ratio produce large changes 

 in the neuron thresholds; high potassium lowers threshold, high 

 calcium raises it. If you have done your conditioning under one 

 set of thresholds of the neuron group, tlien the engram set up 

 would be congruent with that distribution of neuron thresholds 

 in that neuron population. Having once established the pattern, 

 which is more difficult with calcium and easier with potassium, 

 you would need the same balance of thresholds that then existed 

 in order to re-evoke the engram in a given assembly of cells, 

 because various cell thresholds do not change exactly in proportion 

 to the ion ratio. If learnins; was under the normal ion ratio, then 



