PAIN 489 



Beginning of Brochium 

 of Inf. Coliiculus 



Lot. Sp 



Nucleus of Inf. Coliiculus 



FIG. I o. Pain pathways in the mesencephalon. On the left side are shown : the lateral spinotlialamic 

 (inchiding spinotectal) tracts as seen in Marchi degeneration after thoracic cordotomy in man by 

 Rasmussen & Peyton (220), Gardner & Cuneo (87) and Glees C98); and the bulbothalamic tract 

 as seen by absence of Weigert stained fibers seen following infarct by Wallenberg (281, legend to 

 fig. 1 2). On the right side are shown, diagonal hatching, secondary afferent pathways in monkey as 

 seen in Marchi degeneration : the upper medial area after mid-line myelotomy at L5 to 7 ; the lower 

 lateral area after lesion in spinal trigeminal nucleus according to Walker (278). Crosshatching: Lesion 

 in man which produced contralaterally a severe hypalgesia to pin prick on face, analgesia on upper 

 limb and torso and hyperpathia on lower limb (277). 



component might influence the perception of pain by 

 effecting changes in cortical excitabiUty via the 

 reticular formation. Moruzzi & Magoun (194) had 

 shortly before demonstrated the widespread cortical 

 activation from electrical stiinulation in the ventro- 

 medial bulbar reticular formation. Now that stains 

 for axonal degeneration are available Mehler el al. 

 (188) have shown in monkeys, following antero- 

 lateral cordotomy, that there is indeed "a massive 

 fine-fibered, diffuse, medial spinoreticular system" 

 passing to 1 1 of the nuclei in the pontobulbar reticu- 

 lar formation. They also saw in the midijrain fine 

 spinotectal fibers passing to the lateral part of the 

 central gray inatter, the nucleus intcrcoUicularis and 

 deep strata of the superior coliiculus. Bowsher (31) 

 studied four patients following thoracic, cervical or 

 bulbar division of pain pathways using the silver 



stains for axonal degeneration either of Glees (97) 

 or of Nauta & Gygax (199). His results show a strik- 

 ing similarity to those of the previous authors in 

 monkeys. 



Perhaps these spinotectal fibers, or bulbothalamic 

 continuation paths from spinoreticular fibers, are 

 responsible for a sharp spike potential found in the 

 medial inidbrain by Collins & O'Leary (48). When 

 they stimulated the sciatic or superficial radial nerve 

 in cats, they evoked the potential in a discrete region 

 of the reticular substance dorsal to the rostral part 

 of the red nucleus and lateral to the oculomotor 

 nucleus. A relationship to pain was intimated by 

 these facts: a) the potential was activated from 

 peripheral axons of the gamma-delta group, the 

 fastest of which were conducting at 45 m per sec. ; 

 A) its pathway was principally \'ia the ventrolateral 



