M. R. COVIAN, C. TIMO-IARIA AND R. F. MARSEILLAN 443 



contralateral stimulation of the peroneal nerve. The evoked cortical 

 response showed an accentuation ot the positive and an attenuation or 

 disappearance of the negative waves. 



Purpura and Grundfcst (1956) obtained similar depressing effects by 

 intracarotid injection of tubocurarine. By topical application of gamma 

 aminobutyric acid (GABA), Iwama and Jasper (1957) observed an imme- 

 diate and reversible depression in the surface negative component of the 

 primary evoked potential in somatosensory cortex of the cat m response to 

 thalamic stimulation. 



The positive and negative components of the primary response are 

 post-synaptic events. The negative, which seems to signal the depolariza- 

 tion of the apical dendrites, appeared in the findings here reported most 

 sensitive to the action of the reticular formation. It represents the activa- 

 tion of a larger number of neuronal units than the fnst one. This multi- 

 synaptic arrangement would be more susceptible to the action of the 

 unspecific extralemniscal system than it is to the anaesthetics. The alterna- 

 tive of an interaction at a subcortical level has to be taken into account. 



GROUP DISCUSSION 



Olds. We have material on chronic stimulation o( the reticular torniation and 

 its effect on self-stimulation. It seems very interesting in the light of this inhibition 

 of the negative component. We have an animal selt-stimulating with electrodes in 

 the medial forcbrain bundle and we gradually turn up a stimulus m the dorso- 

 medial reticular formation — the sine wave stimulus — up to 10 micro-amperes 

 which is subthreshold for any effect which we could observe from this stimulus 

 alone, self-stimulation comes to a complete halt. Going the other way, the situation 

 is peculiarly just the reverse, if one now has the animal responding to escape from 

 the tegmental stimulus and he now begins to augment stimulation in the medial 

 forcbrain bundle electrode just gradually raising the level, the rate of the escape 

 response is increased. Just what this peculiar interaction may mean I have no idea 

 but it seems interesting enough to put on the record at this time. 



Naquet. Did you try to stimulate the lemniscus; Some years ago, in 1954, 

 working with Drs Magoun and Eve King, we obtained the same results as you, 

 when we stimulated the sciatic nerve or the radial nerve. But when v/e stimulated 

 the lemniscus, the stimulation of the reticular formation provoked sometimes a 

 facilitation of the evoked potentials recorded after the thalamic relay. I think this 

 facilitation was confirmed by Dumont and Dell (ipS^) and Bremer and Stoupel 

 (1958). When they applied a shock on the optic nerve, the stimulation of the 

 reticular formation gives some facilitation on the response record at the level of 

 the cortex. When a flash is used, the stimulation of the same point of the reticular 

 formation provokes a reverse effect or no effect. 



Hernandez-Peon. Perhaps the different results obtanied concerning facilitation 

 and depression of the sensory evoked potentials may be due to the placement of the 

 stimulating electrodes. There is also a difference in the results obtained by an 



