THE EXTRAPYRAMIDAL MOTOR SYSTEM 



897 



grasp reflexes are always particularly pronounced in 

 the flexed extremities. A spastic increase of muscle 

 tone is often, but not always, combined with the 

 forced grasping. .\ kinetic apraxia of the limijs may 

 occur in man along with grasp reactions following 

 lesions of area 6. 



Stimulation of area 4s (the strip region of Hines) 

 produces relaxation of hypertonic muscles or \olun- 

 tary contractions in the contralateral extremities or a 

 slow tonic movement of the ipsilateral fingers, elbow 

 and shoulder [Wyss (298)]. According to Bucy & 

 Fulton (26), these ipsilateral efTects are not mediated 

 in the spinal cord by the pyramidal tract. Destruction 

 of area 4s produces a transitory spastic paralysis 

 which can be enhanced by lesions in area 6 or area 4. 

 McCulloch et al. (179) were able to demonstrate a 

 pathway froin area 4s to the medial reticular forma- 

 tion of the medulla from which the impulses were 

 conveyed to the spinal cord through reticulospinal 

 fibers. These findings are in keeping with Wagley's 

 observations (283) that interruption of the lateral or 

 ventral reticulospinal tract, in addition to the py- 

 ramidal tract, is necessary for the appearance of a 

 spastic increase of muscle tone. The inhibitory fibers 

 of the medial reticular formation reach certain 

 interneurons of the anterior horn. 



Connections of area 4s with the caudate nucleus 

 were found with the strychnine method, but could 

 not be confirmed by the Marchi method [Verhaart & 

 Kennard (265)]. The suppressor effects of area 4s, 

 apparently demonstrated in older experiments, have 

 been largely refuted; this is, however, not true for 

 the motor efTects of stiinulation described here. Ac- 

 cording to the investigations of Travis (257), spastic 

 hypertonus following cortical lesions in the macaque 

 appears only if the supplementary motor area is 

 removed in addition to the precentral motor area. 

 As the corticofugal projections of the supplementary 

 motor area enter the cortical white matter rostrally 

 to the efferents of the precentral motor area, they 

 probably were interrupted in the white matter in 

 earlier experiments in which extensive lesions of area 

 4s were produced. This would explain the spasticity 

 occuring after these lesions. 



The anatomical and electrophysiological topog- 

 raphy of area 6 was first studied by Vogt & Vogt 

 (268). The part having no giant pyramidal cells, 

 located immediately rostrally to area 47, is called 

 area 6aa; in front of this area and covering the 

 convexity and the medial .surface of the brain they 

 differentiated area Sa/J, and in addition areas 6ba 

 and 6b/3 located at the lower end of the central 



gyrus. Later Hines (113-115) separated the strip 

 region (area 4s) from the frontal border of area 

 6aa. Area 8 of Brodmann, which has a very thin fourth 

 layer, constitutes the transition to the granular 

 prefrontal cortex. 



Faradic stimulation of area Gaa produces tonic 

 isolated movements mostly of the large proximal 

 joints of the contralateral extremities, with a tendency 

 to involve the other joints of this limb and of the 

 other limb of the same side. The ipsilateral limbs are 

 also involved and sometimes even first [Bucy & 

 Fulton's ipsilateral representation (26)]. The thresh- 

 old is higher and the responses have a longer latency 

 than those obtained from area 4 and thev outlast the 

 stimulus for a longer time. The safety margin for 

 epileptic seizure activity is much smaller and bar- 

 biturate anesthesia more easily blocks the responses 

 to stimulation of area 6aa. If stronger stimuli are used, 

 an adversive movement of the whole bodN' to the 

 opposite side appears in addition to the tonic isolated 

 movement. The tonic isolated inovement is mediated 

 by area 4, whereas the adversive movement is pro- 

 duced by direct projections to the brain stem [\ ogt & 

 Vogt (268)]. Stimulation of the face area of area 

 Gacn produces complex movements of groups of facial 

 muscles due to excitation of the adjacent area 4 

 [Walker & Green (287)]. 



Area 6a(3 [Vogt & Vogt (268)], when stimulated 

 with threshold stimuli, gives rise to adversive move- 

 ments mediated by direct efTerent fibers. In monkeys 

 this is true both for the areas covering the convexity 

 and the medial surface of the brain. Stronger stimuli 

 produce additional tonic isolated movements, con- 

 sidered to result from propagated excitation of area 4. 

 Lesions of area 6a|fl are followed by the appearance of 

 a grasp reflex without spasticity. 



Stimulation of area 6ba even with weak currents 

 produces rhythmical movements of the mouth and 

 the lips, chewing and swallowing movements as well 

 as salivation [Vogt & Vogt (268)]. These efTects are 

 mediated by direct efferent paths and remain un- 

 impaired after removal of area 4. 



Weak stimulation of area 6b/3 and of its dorsal 

 continuation in area 87 elicits inhibition of respira- 

 tion or of the rhythmic chewing, swallowing, mouth 

 and respiratory movements which can be obtained by 

 stimulation of area 6ba. These movements are 

 mediated by direct centrifugal pathways. Stronger 

 stimuli also produce adversive movements [Vogt & 

 Vogt (268)]. Stimulation of area 8 produces opening 

 of the eyelids and conjugate lateral movement of the 

 eyes sometimes with turning of the head to the op- 



