CINGULATE, POSTERIOR ORBITAL, ANTERIOR INSULAR AND TEMPORAL POLE CORTEX 



1355 



cingulate region, which facilitated cortically initiated 

 mosements witliout influencing the knee jerk ( 1 26, 

 185). Facilitatory responses appear to be favored by 

 chloralose and may at times lie converted to inhibi- 

 tion by additional administration of barbiturates 

 (126). No re\ersal of the effects has been obtained by 

 \arying the stimulus characteristics (126). Both facili- 

 tation and inhibition are independent of accom- 

 panying respiratory or arterial pressure alterations 

 (126). They are exerted upon flexor and extensor 

 moveinents indiscriminately {58, 126) and in a non- 

 somatotopic manner (126). The effects are present 

 also in mono- and polysynaptic reflex discharges of 

 the ventral spinal roots (126). Like most other central 

 motor areas the medial and basal inhibitory and 

 facilitatory zones influence the intrafusal fibers of the 

 muscle spindles through the small-sized 7-motoneu- 

 rons prior to their effect on the large-sized a-moto- 

 neurons of the ventral horn (94). 



Regarding the site of the facilitatory and inhibitory 

 action, both may he produced in the absence of any 

 alteration of the electrical acti\ity in the motor cortex 

 (58, 126, 232) or after removal of the cortical sensory- 

 motor areas (126, 232). However, besides acting 

 directly 'downstreain,' facilitation of cortically in- 

 duced movements may also be obtained at a cortical 

 lev^l, dependent on corticocortical connections (126, 

 232). 



The similarity of the inhibition of somatomotor ac- 

 tivities obtained from the most sensitive two medial 

 and basal cortical zones herein discussed to that 

 produced by stimulation of the central end of the 

 cut vagi (as shown in fig. 5Z), F) has been emphasized 

 (126, p. 137). The orbital surface of cats and monkeys 

 has been considered as a sensory-motor vagus repre- 

 sentation; excitation of the vagus nerve may influence 

 the electrical activity in this cortical area (18, 55, 56, 

 116), and various autonomic responses, such as alter- 

 ations in arterial pressure and gastrointestinal motility, 

 apparently similar in every respect to those obtained 

 by direct central and peripheral vagus stimulation, 

 can be provoked from this cortical field (see below). It 

 is believed (126, p. 137) that the inhibition of somato- 

 motor activities produced from the orbital surface 

 merely represents one of the many "vagal' activities 

 which this region seems to display. Afferent impulses 

 in the vagi and descending impulses from the cortical 

 vagus motor field apparently act upon the same brain- 

 stem mechanism producing similar visceromotor and 

 somatomotor responses. The demonstration of identi- 

 cal autonomic and inhibitory somatomotor effects 

 from the anterior insula and temporal pole in monkeys 



has suggested that the cortical vagus representation 

 also extends into these zones and, further, that a 

 'second" vagus representation resides in the genual 

 portion of the anterior cingulate cortex (126). Re- 

 garding the proposed second vagal representation in 

 the latter area, it is relevant to recall the recent 

 demonstration of an afferent x'agal projection to the 

 pre- and subgenual portion of the anterior cingulate 

 area (55, 56, 116). This ascending path courses 

 through the anterior hypothalamic, preoptic and 

 septal areas, as does possibly the descending path 

 mediating the "vagal' visceral and the somatic inhibi- 

 tory effects from the same cortical zone (cf. below). 



The type of response consisting in facilitation of 

 cortically and reflexly induced movements — asso- 

 ciated with inhibition of respiration, other sponta- 

 neous mo\ements (as shown in fig. 5C), and motor 

 after-discharges — is quite similar to that induced from 

 parts of the thalamic reticular system (13, 117, 120; 

 126, p. 158). It seems likely that both quieting of 

 prestimulatory spontaneous inovements and the facili- 

 tation represent integrated parts of the complex 

 "awakening," 'arousal' or "attention" response which 

 can be produced on high-frequency stimulation of 

 these cortical and thalamic areas in unanesthetized 

 animals. The "arousal' seen in the electrocorticogram 

 and the pupillodilation on stimulating the same areas 

 provide further support for this assumption. The 

 brain-stem activating system can be influenced not 

 only by peripheral ascending impulses, as first demon- 

 strated by Moruzzi & Magoun (182), but also by 

 corticofugal impulses from these medial and basal 

 areas of the forebrain (70; 126, p. 240). These areas 

 appear to share this "arousal" function with the lateral 

 frontal, occipital and temporal fields, stimulation of 

 which has been shown to exert a similar quieting effect 

 on spontaneous movements (figs. 2, 4.4). There seems 

 to be a close coincidence between these areas and those 

 recently shown to project into the brain-stem reticular 

 system (70). The same areas also cause a similar 

 'arousal' of the electrocortical activity (126, 225; 

 Kaada & Johannessen, unpublished observations) 

 and of the behavior of the nonanesthetized animal by 

 stimulation through implanted electrodes (118, 119, 

 130, 131, 223; Fangel & Kaada, unpublished observa- 

 tions). 



The apparently contradictory results reported by 

 various authors regarding the "suppression" of motor 

 responses on anterior cingulate stimulation are pos- 

 sibly due to the fact that various overlapping portions 

 inside this area subserve different functions and there- 

 fore respond differently. One portion appears to be 



