UNSPECIFIC THALAMOCORTICAL RELATIONS 



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FIG. 2. Tripping of spindle 

 bursts in six different cortical 

 areas in response to a single 

 shock in tine intralaminar nucleus 

 centralis medialis of the cat under 

 pentobarbital anesthesia. 



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L OC 



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I SEC. 



25-3 



recruitins; with less waxing and waning from rostral 

 thalamic stimulation. Nevertheless responses show 

 a wide distriiiution over many areas of cortex. Here 

 one often obtains a mixture of specific and unspecific 

 effects making analysis difficult. 



The recruiting respon.se is not always of stirface 

 negative electrical sign. When the surface of the 

 cortex is depressed i)y exposure, or by the local appli- 

 cation of procaine, the response may be entirely 

 surface positive. It may also be diphasic with an 

 earlier surface positive phase of smaller amplitude. 

 Early positive phases may be due, however, to con- 

 tamination by simultaneous stimulation ol some 

 specific projection fibers which produce short-latency 

 initially surface-positive responses. There may be a 

 typically surface-negative respon.se in one cortical 

 area simultaneous with a predominantly surface- 

 positive wave in another area, the latter area u,sually 

 being under less complete control by the recruiting 

 system at a particular site of thalamic stimulation. 



MICROELECTRODE STUDIES OF RECRUITING RESPONSE 



The intracortical distribution of unspecific afferent 

 projections from the thalamus has been shown to be 

 distinct from that of specific afTerents by microelec- 

 trode studies (45, 46). The surface negative wave of 



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(0 



FIG. 3. Oscilloscope record of single waves of recruiting re- 

 sponses in the precruciate cortex of the cat, evoked by stimula- 

 tion of n. ventralis anterior (VA) and n. centrum medianum 

 (CM), respectively. Speed of sweep is indicated in 5 and 10 

 msec, time lines below. 



the recruiting response becomes a deep positive wave 

 when recorded with a microelectrode inserted to a 

 depth of 0.7 to i.o mm beneath the surface. It repre- 

 sents, therefore, a wave of depolarization located in 

 the more superficial cortical layers, comparable in 

 this respect to the late surface negative wave of the 

 specific evoked potential complex. 



Indi\idual neurons, which fire with short latency 

 in the deeper layers of the cortex in respon.se to a 

 specific afferent volley, are not fired directly by 

 impulses arriving o\er unspecific afTerents. However, 

 the excitaijility of these specific cortical cells can be 

 modified so that they show increased firing to the 



