UNSPECIFIC THALAMOCORTICAL RELATIONS 



'317 



FIG. 9. Simultaneous record- 

 ings from the anterior sigmoid 

 gyrus [upper trace) and medullary 

 pyramid {lower trace). Top: Aug- 

 menting responses initiated in an 

 unanesthetized cat by stimu- 

 lation of n. ventralis lateralis; 

 note the 'relayed' pyramidal 

 volleys. Aiiddte: Similar record- 

 ings from another preparation, 

 recruiting response initiated by 

 stimulation of n. reuniens; note 

 the stability of the pyramidal 

 recording. Bottom: Recordings 

 taken during a spontaneous 

 spindle burst in an unanesthe- 

 tized cat with mesencephalic 

 thermocoagulation; note the re- 

 layed spindle waves in the 

 pyramidal recording. [From 

 Brookhart c& Zanchetti I 12).] 



for also if the unspecific fibers arc small, unmyelin- 

 ated and with slow conduction velocity. 



Under certain conditions it is possible to show a re- 

 markable degree of independence between augment- 

 ing and recruiting waves in the same area of the cor- 

 tex, as was demonstrated by Brookhart & Zanchetti 

 (i2j. Augmenting and recruiting responses may be 

 readily confused in experimental studies since it is of- 

 ten hard to avoid stimulation of both specific and un- 

 specific thalamic fibers at the same time. The aug- 

 menting responses are not as closely related to the 

 spontaneous spindle bursts as are recruiting waves (56) 

 since spindle bursts may appear intermingled with 

 augmenting waves while they are usually more com- 

 pletely driven by unspecific thalamic stimulation. The 

 augmenting responses are probably more closely re- 

 lated to the neuronal systems of the local sensory 

 after-discharge (15). 



There may be a more intimate interrelationship be- 

 tween specific and unspecific projection systems in 

 association areas of the cortex, but the details of this 

 relationship have yet to be worked out. 



RELATION BETU'EEN THALAMIC AND BRAIN-STEM 

 ASCENDING RETICULAR ACTIVATING SYSTEMS 



It seems clear that a considerable proportion of these 

 ascending activating effects obtained from the basal 

 diencephalic and midbrain portions of the reticular 

 system are mediated to the cortex by means of the tha- 

 lamic reticular system (53). As has been stated above, 

 the spontaneous rhythmic activity of the cortex can be 

 blocked, producing an activation pattern, by rapid 

 stimulation within either the thalamic or the midlarain 

 portions of the ascending reticular systems. 



