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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



sions much more in accord with other data ahhough 

 some of their findings are puzzhng. First of all, they 

 established that the potentials evoked in the contra- 

 lateral SI and SII (contralateral in respect to the 

 stimulated nerve) can be relayed both through the 

 ipsilateral dorsal column and through the contra- 

 lateral anterolateral one. This is, of course, expected 

 from the classical studies. However, such potentials 

 seem to be relayed as well through the anterolateral 

 column on the side of the stimulated nerve. While 

 electrophysiological evidence concerning the existence 

 of an ipsilateral pathway is, as already mentioned, 

 quite in harmony w'ith other data, the finding that 

 the discharges in this tract can relay also to the contra- 

 lateral cortex is anatomically not at all self-evident. 

 Thus, despite some ofjservations to the contrary it 

 must be assumed that destruction of an antero- 

 lateral column causes only ipsilateral terminal degen- 

 erations in the thalamus. Likewise it is doubtful 

 despite repeated affirmative reports that spinotha- 

 lamic fibers actually cross partly within the posterior 

 commissure. The latter doubt is reinforced by findings 

 of Gardner & Morin (85) which imply that all cross- 

 ings of sensory paths must take place below the mid- 

 brain. It appears then that, if the contralateral cortex 

 is indeed activated via the anterolateral column of 

 the same side as the stimulated nerve, the route by 

 which this takes place is yet to be determined. 



In preparations in which the anterolateral column 

 of the same side was the only column available for 

 conduction the contralateral cortical potentials were 

 sometimes not evokable, and if evoked sometimes 

 displayed longer latencies than in the intact animals 

 (83). This suggests perhaps that other than the 

 classical pathways might have been involved in the 

 transmission of the discharges. 



There is only fragmentary information available in 

 regard to the ipsilateral responses in SII. It might be 

 reasonable to expect that such responses are con- 

 ducted through the ipsilateral spinothalamic path- 

 way. However, out of three animals (83) in which this 

 path was presumably cut the ipsilateral cortical 

 responses disappeared in only one. Clearly, more data 

 are needed before any conclusions can be drawn. 



The question of the existence of an ipsilateral path- 

 way from the nuclei of the posterior column to the 

 ventrobasal complex aroused considerable interest. 

 Several workers (26, 51, 116) using sectioning tech- 

 niques concluded that such a pathway exists. How- 

 ever, in our opinion both the anatomical and the 

 functional evidence (see p. 400) implies rather defi- 

 nitelv that such conclusions must have been in error. 



The problem of whether discharges evoked by 

 stimulation of the afferent nerve may ascend within 

 the spinal cord by other than the dorsal column or 

 spinothalamic pathways has been considered re- 

 peatedly (41, 91, 176) and some evidence has been 

 adduced that this may be the case. Morin (176) pro- 

 posed that one such pathway runs in the dorsal part 

 of the lateral column and that it synapses in the nu- 

 cleus cervicalis lateralis. A crossing to the other side 

 is believed to take place at the upper cervical levels. 

 N. cervicalis lateralis, however, has been asserted 

 (205, 206) to relay exclusively to the cerebellum, a 

 finding strongly contested by Morin & Catalano 



(177)- 



In summary it appears that observations of evoked 

 potentials after sectioning various fiber tracts have 

 yielded thus far only limited data. The important 

 finding is that impulses from both sides of the body 

 are conducted in each anterolateral column. Some 

 equivocal or contradictory results may be due in part 

 to the difficulties in distinguishing in acute experi- 

 ments the shock due to the acute lesion itself from the 

 results of destruction of the relevant fibers. It is also 

 possible that a massive electrical stimulation of the 

 nerve might contribute to some confusing findings. 

 Whatever the reasons may be for the difficulties 

 encountered, much more systematic work is needed 

 with this technique. 



Centrijugal Pathiva\s Impinging Upon Sensory 

 Somatic Synaptic Regions 



It is implicit in many present day concepts concern- 

 ing the organization of the central nervous system that 

 synaptic regions situated orally in a pohsynaptic 

 chain of an afferent system are capable of modulating 

 the \ery inflow which arouses their activity. However 

 well founded such ideas may be, no rigorous proof has 

 thus far been offered for the existence of such circuits 

 in the somatic sensory system, although recently 

 suggestive evidence to this effect has been ad\anced. 

 Thus, Brodal et al. (34) and Walberg (248) have 

 described direct Ijilateral corticofugal connections to 

 the sensory trigeminal elements and to the gracile and 

 cuneate nuclei, arising not only from the sensorimotor 

 area but from all major cortical regions as well. The 

 former connections would clearly represent a ' feed- 

 back' system. It is certainly unexpected that virtually 

 all cortical regions should affect the essential compo- 

 nents of the projectional tactile system in a basically 

 identical fashion. The lack of any somatotopical 

 organization of the projection arising in the somatic 



