[314 HANDBOOK OF PHYSIOLQGV ^^ NEUROPHYSIOLOGY II 



» 7 < 5 * 3 2 



FIG. 6. Diagram of the thalamic reticular system as determined by stippled areas showing recruiting 

 responses to local repetitive stimulation in the cat. Cross sections of stereotaxic frontal planes 12, 

 10, 7.5 and 6 are shown. The double stippling in the ventral portion of nucleus ventralis anterior 

 indicates the region where rostrally conducting pathways are most dense. 



ally a very definite and distinct ('specific') ganglionic 

 organization of cells and fibers. When searching for it 

 in the thalamus with a small bipolar stimulating elec- 

 trode, using weak electric currents (the threshold is 

 of the order of 2 to 4 v. for i msec, pulses), one finds 

 that movement of the electrode only a fraction of a 

 millimeter will suddenly cause large responses to ap- 

 pear which were ai)sent before. It is not, therefore, a 

 system of neurons diffusely distributed throughout the 

 thalamus. It cannot be activated bv stimulating within 



sensory relay nuclei nor from within other specific 

 thalamic nuclei with the exception of certain border 

 zones mentioned above. The terms 'imspecific" or 

 'diffuse" applied to this system may be misleading. 

 These terms refer particularly to the widespread dis- 

 tribution of cortical responses, with only a loose re- 

 gional topographical organization, in contradistinc- 

 tion with the relatively restricted local projections of 

 diff"erent portions of specific nuclei. The thalamic dis- 

 tribiuion is also extensive, but not diffuse. 



