SENSORIMOTOR CORTICAL ACTIVITIES 



8i 



spastic hemiplegia appeared wliich resol\ed gradually 

 and incompletely in the ensuing 5 years. Area 6 and 

 part of area 4 were then excised on the right, leading 

 to a left spastic hemiparesis and a transient accentua- 

 tion of the paresis and spasticity on the right side. On 

 sub.sequent ablation of the right postcentral gyrus, all 

 extremities showed extreme paresis and spasticity 

 which were more severe and persistent on the right. 

 Further details are available (80, 204, 232). 



Cingulate Gyrus 



In view of the complexity attributed to the func- 

 tions of the limbic cortex, reference should be made to 

 Chapters LIV to LVIII of this work for a compre- 

 hensive review of the subject. Only those aspects of 

 cingulate functions bearing on motor activities, and 

 particularly those evoked from anterior cingulate 

 areas, will be considered here. 



Anatomical descriptions of the limbic cortex and its 

 subdivisions in the rat (431), rabbit (377), cat (377) 

 and primates (446) have been extensively reviewed 

 (cf. 377) with attention to the phylogenetic aspects of 

 this problem. Projections to this cortex from the an- 

 terior nuclei of the thalamus have been described 

 (379; cf. 377). Corticocortical connections of the 

 cingulate gyrus are far from completely understood. 

 Strychnine neuronography has failed to reveal cortical 

 association fibers to area 24 (294), but anatomical 

 studies have described connections from the pre- 

 frontal cortex to the anterior cingulate region both 

 in man and in monkey (cf. 7). The paracentral lobule 

 may also have connections with the cingulate gyrus 

 (240). A cingulate belt, lying along the lip of the 

 cingulate gyrus and including also most of area 32 of 

 Brodmann, has been considered to receise afferents 

 from the 'suppressor strips' (35) and area 24 (123). 

 Projections from area 24 to some portion of the pre- 

 central motor cortex, particularly area 6, have also 

 been described (178, 468). There is evidence for pro- 

 jections from area 24 to the caudate nucleus {135, 

 294), anteromedial nucleus of the thalamus (342, 

 400), septal areas (178) and brain stem (cf. 466), but 

 the last have not been confirmed (178). Other con- 

 nections have been described between the cingulate 

 and other parts of the limbic system (cf. 7), but their 

 relationship to motor functions may be remote. 



Although area 24 of Brodmann has been included 

 in the so-called 'suppressor areas" (294, 295), the 

 effects elicited by its stimulation are quite different 

 from those said to characterize the phenomenon of 

 'suppression' (see below). Stimulation of cingulate 



cortex in acute experiments in the cat and monkey 

 will alter cortically-induced movements in the direc- 

 tion of facilitation (224, 401, 469), of inhibition (208, 

 224, 237, 401, 404) or of facilitation reversing to in- 

 hibition (401). Anesthesia greatly modifies the ob- 

 ser\-ed responses (401, 469). Loss of muscle tone and 

 abolition of deep reflexes also occur (404, 466). These 

 stimulations produce irregular alterations in cortical 

 electrical activity, which are not necessarily correlated 

 with inhil)ition or facilitation of cortically-induced 

 mo\ement, suggesting that these efTects may arise 

 through subcortical mechanisms (401). However, 

 according to Sloan & Kaada (401), some of the 

 facilitatory eff"ects might be mediated by cortico- 

 cortical fibers. 



In animals with and without anesthesia, gross, slow 

 movements of tonic type have been observed to follow 

 stimulation of anterior limbic cortex (198, 224, 225, 

 237, 466) which may result from 'downstream' influ- 

 ences at subcortical levels (198). Inhibition of spon- 

 taneous muscular activity has been seen with chroni- 

 cally implanted electrodes (401, 469), but these 

 results are disputed (22, 91 j. Relationships with 

 cerebellar mechanisms have been discussed (187, 

 263). Autonomic responses have also been reported, 

 but these effects are variable and inconstant. This 

 subject is discussed by Kaada in Chapter L\' of this 

 work. 



Early experimental investigations of the effect of 

 ablation in the cingulate cortex have been reviewed 

 by Ward (466) who found no changes in motor 

 control, deep reflexes, muscle tone or resistance to 

 manipulation. A review of similar experimental re- 

 sults by other investigators, both in animals and man, 

 is also available (343). Permanent involuntary 

 grasping has been found after combined lesions of 

 the cingulate gyrus and area 6 (374). Kennard (233) 

 has described altered placing and hopping responses 

 after bilateral anterior cingulate ablation. This would 

 appear an isolated observation of involvement of the 

 motor system. Kennard suggests that the hypomo- 

 tility and inertia, said to occur both in monkey and 

 man after cingulate ablation (cf. 368, 466, 467), may 

 be regarded as a motor deficit or dyspraxia. The re- 

 maining aspects of the symptomatology which sug- 

 gest the participation of the limbic cortex in the 

 organization of patterns of motor performance in 

 relation to behavior are discussed by Brady in Chapter 

 LXIII of this work in connection with the possible 

 involvement of limbic cortex in emotional functions 

 (cf. 367, 368). 



