288 BRAIN MECHANISMS AND LEARNING 



Electrographically (and even under Flaxcdil) T masked potentials 

 evoked by SS on contralateral sensory cortex; amplitude and duration of 

 individual waves were reduced markedly (initial spike was resistant). 

 T effects were compared clectrographically as to quality, intensity and 

 distribution with results induced by application of other agents known to 

 reduce cortical evoked potentials (e.g. SS voltage reduction; EEG 

 'activating' influence as brain stem stimulation or presentation of novel, 

 intense or conditioned sounds). T effects exhibited specificity: non- 

 reinforced tones of different frequency become ineffectual; T influence 

 could be restricted to the somatic sensory areas. 



T application was followed by EEG 'activation', generalizeci or localized 

 (to sensory cortices and to nucleus mcdialis dorsalis of thalamus); delayed 

 and transitory reinforcement of slow rhythms also occurred. 



Experiments indicated that changes (behavioural, EEG) induced by 

 painful stimuli are subject to variations 'spontaneous' anci provoked; they 

 indicated, moreover, that learned issues established through adequate 

 training are significant. 



GROUP DISCUSSION 



Gerard. In less careful terms than you used, how long can you fool the cat into 

 thinking that it does not hurt; 



Segundo. For a period of 10-30 seconds; after that and it shocks were continued, 

 cats reassumed the characteristic attitude and potentials returned to their initial 

 amplitude. 



Gerard. Is the sound effect extinguished; 



Segundo. Tone effects will be extinguished it sounds are repeated without their 

 usual 'reinforcement' by shock interruption. 



Myers. I found it very exciting to hear, Dr Seo;undo, that the animals in vour 

 experiment did not differentiate between opposing extremities in responding to 

 the conditioning stimuli. Such a result closely resembles the findings of Anrep and 

 others working with tactile conditioning in the dog. Specifically, they found that 

 after a positive conditioned salivary response had long been established to tactile 

 stimulation of a given skin area on one leg, first stimulation of the homologous 

 locus of the opposite leg also gave profuse salivary flow, whereas stimulation of 

 nearby loci on either side gave litde if any salivary response. Furthermore, it was 

 not found possible to establish separate conflicting reflexes to tactile stimulation of 

 the separate homologous skin loci. Rather, as the response to tactile stimulation of 

 one locus changed character, that of its homologous locus tended always also to 

 change 'spontaneously' in the same direction, the change in the homologous locus 

 occurring without direct conditioning through its own receptor field. Thus was 

 demonstrated a remarkable mirroring or symmetry of development of tactile 

 'gnosis' over both sides of the body surface subsequent to one-sided conditioning. 

 Bvkov subsequently found that section o{ the corpus callosum disrupted this 



