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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



related to "vagar activities and iiiliibits cortically 

 and reflexly induced movements; another portion 

 seems to be related to the 'arousal' mechanism and 

 facilitates cortically initiated movements. Arrest of 

 prestimulatory somatic movements is common to the 

 two different patterns of activity and may possibly 

 have a different functional significance in the two 

 patterns. The cortically induced 'arousal' appears to 

 be rather sensitive to anesthesia (126, 225; Fangel & 

 Kaada and Kaada & Johannessen, unpublished 

 observations) and thus it may be that stimulation of 

 a given point may facilitate a cortically induced 

 movement in the unanesthetized or lightly anes- 

 thetized animal, whereas the same stimulation may 

 cause inhibition after the 'arousal' paths have been 

 blocked by anesthesia. Inhibition from the anterior 

 cingulate and orbitoinsulotemporal 'vagal' zones 

 may persist into the deepest stages of anesthesia (126). 

 The conversion of respiratory acceleration to inhibi- 

 tion by administration of barbiturates, mentioned 

 previously, and the reversal of arterial pressure re- 

 sponse from decrease to increase after vagotomy (240) 

 may possibly be similarly explained. 



The inhibition of respiratory and other spontaneous 

 movements and of muscular tension by excitation of 

 the olfactory pathways in the uncal region are pos- 

 sibly related to the sense of smell as inhalation of 

 various vapors and irritants may cause a similar 

 profound inhibition of movements and muscular tone 

 {6, II, 67). 



The possible corticosubcortical routes mediating 

 the inhibitory (including respiratory) and facilitatory 

 somatic effects evoked from these cortical zones have 

 been discussed in detail elsewhere (126, pp. 146-160). 

 Although not yet proved, there is some experimental 

 evidence for a hypothalamic route (possibly through 

 the ventromedial hypothalamic nucleus) for the 

 inhibitory influences from the medial and basal 

 'vagal' cortical zones yielding optimum inhibitory 

 effects. This nucleus appears to represent a focal area 

 for a number of fiber systems concerned with the 

 control of autonomic functions (46) and with inhibi- 

 tory effects on somatomotor activities (126, p. 153). 

 Direct stimulation of the ventromedial nucleus pro- 

 duces a strong inhibitory influence on spontaneous, 

 reflexly and cortically induced movements (13) as 

 does stimulation of the anatomically demonstrated 

 projections to this nucleus from the posterior orbital 

 surface via the preoptic region and medial forebrain 

 bundle (46, 215), from the olfactory tubercle (49), 

 from the pyriform cortex via the amygdala (126, 144) 

 and stria terminalis (13, 126, 144), and hom (he 



anterior cingulate and subcallosal cortex via the 

 .septal and preoptic areas (13, 91, loi, 102, 135, 170, 

 265). The recent studies by Turner (256), concerning 

 the respiratory inhibitory path from the posterior 

 orbital surface, and by Hodes et al. (114), concerning 

 the path for bilateral inhibition of the knee jerk from 

 the rostral portion of the anterior cingulate cortex, 

 are consistent with this assumption. More caudally 

 the respiratory inhibitory effects from the orbital 

 cortex are carried downward, possibly by a bifid 

 pathway, to the reticulum of the pontine brain stem 

 outside the caudate nucleus (256). According to 

 Poirier & Schulmann (195) the respiratory (and 

 arterial pressure) effects evoked from the temporal 

 pole are dependent on a path coursing ventrolateral 

 to the optic tract towards the pulvinar. 



The weaker inhibitory effects on respiratory and 

 other spontaneous somatic movements (associated 

 with the 'arousal' response, without loss of muscular 

 tone) obtained from the more extensive medial and 

 orbitoinsulotemporal zones are possibly mediated via 

 the thalamic and brain-stem reticular system (118, 

 1 19, 126). The same appears to be true of the bilateral 

 facilitatory effects on corticallv induced movements 

 (126, p. 156; 185). 



TONIC .-"iND CLONIC MOVEMENTS. Slow tonic movements 

 of the limbs, trunk and neck, mostly extensor and con- 

 traversive in type, ha\e been observed by various 

 investigators on stimulating the anterior cingulate 

 (126, 147, 232, 266), subcallosal (126), posterior 

 orbital (126, 215), anterior insular and temporal polar 

 cortex (73, 126, 133) in anesthetized animals. .Showers 

 & Crosby (227) describe a pattern of somatotopic 

 movements obtained by stimulation of the anterior 

 cingulate region which may be elicited in a reversed 

 order from the stimulation of the posterior cingulate 

 region. The elicitation of such movements requires a 

 light level of anesthesia and they most likely represent 

 fragments of the more complex movement patterns 

 seen on stimulating the same areas in nonanesthetized 

 animals (103, 118, 119, 126, 130, 131, 232). The 

 movements may be induced after bilateral ablation 

 of the motor areas (126, 232) and cannot be attributed 

 to either spread of current or reaction to pain (215). 



Twitching of the facial musculature and, occa- 

 sionally, jerkv movements of the neck and shoulders 

 have been observed on stimulation of the anterior 

 cingulate (126, 153, 232) and anterior pyriform cortex 

 and the amygdala (25, 126, 246, 258). 



Tonic contraversive turning of the head and usually 

 also of the eyes is frequently seen in temporal lolje 



