892 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



fibers, which constitute the medial border of the 

 fasciculus lons;itudinalis medialis. They send col- 

 laterals to all the eye muscle nuclei (fig. 8) and termi- 

 nate in the interneurons of the anterior horn of the 

 cervical cord and in the nucleus of the accessory 

 nerve. In all experiments yielding a permanent 

 rotatorv posture of the head the.se fibers show de- 

 generation (see fig. 10). The.se findings confirmed the 

 conclusions of Muskens (196) who.se lesion experi- 

 ments in 1 91 4 had led him to regard this structure as 

 responsible for rotatory postures. 



Furthermore, many fibers also leave the nucleus 

 interstitialis in rostral and lateral directions. It is 

 not yet known whether these fibers are collaterals of 

 the interstitiospinal fibers or whether they are axons 

 of smaller nerve cells of the nucleus interstitialis. 

 In tiie rostral direction fibers go (fig. 8) a) to the 

 nucleus ventro-oralis thalami (V'.o.i.), h) to the nucleus 

 reticulatus thalami, laterally from the \entrocaudal 

 nuclei, and c) to the nucleus entopenduncularis and 

 nucleus sui:)thalamicus via the ansa mesencephalica 

 ascendens. Weak stimulation of all these fibers pro- 

 duces rotatory movements. There is still no evidence 

 as to whether this is also true for the fibers connecting 

 the nucleus interstitialis to the nucleus niger and the 

 supraoptic commissure of Ganser. Only the most 

 mediallv located fibers of the brachium conjunctivum 

 can produce slight head rotation following electrical 

 stimulation, according to Hess & Akert (no). These 

 fibers terminate partly in the nucleus ventro-oralis 

 internus of the thalamus where they become con- 

 nected with the eff'erent mechanism for rotation. 

 These fibers originate in the medial cerebellar nuclei 

 where Koella (152) in 1955 demonstrated rotatory 

 movements with a technique similar to that of Hess. 

 The nucleus interstitialis also receives afferent 

 vestilnilomesencephalic fibers from the ipsi- and 

 contralateral side, partly originating in the nucleus 

 vestibularis superior of von Bechterew. These rotatory 

 effects are to be regarded physiologically as com- 

 pensatorv movements following rotatory stimuli, 

 equivalent in effect to artificial electrical stimulation 

 of the fiber connections of the nucleus interstitialis. 



NEURON.\L MECH.-SiNISMS OF UPW.^RD MOVEMENTS. Low- 



frequency threshold stimulation of the areas located 

 medially and rostrally to the nucleus interstitialis (as 

 shown in figs. 8 and g) induces upward movements of 

 the head and the anterior body which show syn- 

 chrony with the stimulus frequency up to a rate of 8 

 per sec. .Simultaneously the animal opens the eyelids, 

 its pujiils dilate, and the animal looks awake and 



FIG. q. Location in the cat dienccphalon of points the stimu- 

 lation of which produces direction-specific motor responses of 

 the head and body. Left: Frontal section at the level of the 

 posterior ventral nuclei iV) of the thalamus (Th.), H-fields (H) 

 and corpus mammillare {cm.). Ri^hl: Horizontal section show- 

 ing the landmarks of the fornix (Fo), tract of Vicq dWzyr 

 {V.dW.'), tractus Meynert (Tr.M.) and posterior commissure 

 (C.p.). The responsive areas are represented by hatched lines, 

 broken lines or circles. The responses are indicated by symbols 

 plotted in the center of the region from which they were evoked. 

 Note the distribution of the fields with partial overlapping in 

 horizontal and frontal planes. Perhendiculur hatching indicates 

 lowering,, perpendicular broken lines, elevation; circles, rotation in 

 the frontal planes; horizontal hatching, contraversive deviation in 

 the horizontal plane; horizontal broken tines, ipsiversive deviation 

 in the horizontal plane. [Redrawn after Hess et al. (iii) and 

 Hess (107).] 



slightly excited. If stronger stimuli are used, the 

 contralateral shoulder and the forelimbs, but rarely 

 the hind limbs, are involved. If the head is fixed, both 

 eyes show conjugate vertical movements (87). 



Coagulation of an area producing upward move- 

 ments leads to a mirror-image defect: lowering of the 

 head and anterior part of the body. Bilateral total 

 destruction of the structures responsible for these 

 movements produces a continuously lowered posture 

 of the head, the chin leaning on the floor. Simul- 

 taneously there is also a loss of the ability to follow 

 objects with the eyes in the vertical upward direction. 

 Thus, it appears that the mechanism for upward 

 movements is also tonically active during wakefulness. 

 If there is an additional bilateral lesion in the dy- 

 namogenic zone of Hess in the posterior hypothalamus, 

 the cats are drowsy, hardly react to environmental 

 stimuli and do not correct uncomfortable postures. 



