THE EXTRAPYRAMIDAL MOTOR SYSTEM 



893 



FIG. 10. Mirror-image effects on head 

 position of stimulation and coagulation 

 in the interstitial nucleus. Upper left: 

 Stimulation (0.5 v., 8 per sec.) of the 

 left interstitial nucleus causes rotation 

 of the head to the left. Upper right: One 

 day after coagulation at the stimulation 

 point there appears a mirror-image ro- 

 tation of the head to the right. Lower: 

 The anatomical correlate of the rotated 

 posture of the head i.s the degenerated 

 intcrstitiospinal tract {is. spi). The stim- 

 ulation point lies 0.5 mm more laterally. 

 [From I lassler & Hess (91)-] 



The tonic coordinating mechanisms mediating 

 upward movements are located in the ventroanterior 

 mesencephalon dorsocaudally to the mammillary 

 bodies and rostroventrally to nucleus interstitialis, 

 according to Hassler (87). Their anatomical substrate 

 is the nucleus prestitialis which is also called the 

 nucleus interstitialis ventralis or inferomedialis (fig. 

 8). This nucleus has the following efTerents which 

 evoke more or less pure upward movements around 

 the transverse axis on electrical stimulation: a) the 

 descending fasciculus prestitiolongitudinalis found 

 medially within the fasciculus longitudinalis medialis 

 sending collaterals to all eye muscle nuclei and ending 

 with a few thin fibers in the anterior horn of the 

 cervical cord; h) the tractus tegmenti medialis, 

 first described by Ogawa, which lies parallel to and 

 slightly ventral to the fasciculus longitudinalis 

 medialis and which sends its descending fibers down 

 to the medial accessory olive, thus conveying im- 

 pulses for upward movements to the cerebellum; 

 c) the prestitiohypothalamic fibers passing rostrally 



through the hypothalamus along the external border 

 of the central grey which convey impulses to hypo- 

 thalamic mechanisms correlated with emotional 

 reactions; and d) the prestitiorubral fibers going in a 

 caudal direction to the anterior part of the nucleus 

 ruber (see fig. 8). The efferent pathway of the nucleus 

 ruber, the rubrospinal tract, produces raising of the 

 head and anterior body when stimulated electrically, 

 as shown by Hess & Weisschedel (i 12). This pathway 

 provides the mechanisms for upward movements 

 with a fast conducting descending pathway to the 

 anterior horn system. In contrast to the nucleus 

 prestitialis and its pathways, the tractus rubrospinalis 

 is not maintained in tonic activity (87). Less con- 

 spicuous connections are also made from the nucleus 

 prestitialis to the nucleus entopeduncularis and to 

 the pallidum. These fibers connect the statokinetic 

 systems with the extrapyramidal centers. 



NEURONAL MECHANISMS OF DOWNWARD MOVEMENTS. 



Physiological investigation of the mesencephalon 



