SENSORIMOTOR CORTICAL ACTIVITIES 



809 



cardiac acceleration, vocalization or arrest of speech 

 (358). The movements of skeletal musculature were 

 described as 'tonic contractions of postural type.' 

 During epileptic attacks, arising from a focus in this 

 area, similar tonic movements occur in which the 

 whole body participates (357)- Bates (41) found that 

 stimulation of the medial aspect of the human hemi- 

 sphere after hemispherectomy will induce movements 

 of the ipsilateral extremities almost to the same extent 

 as can be produced voluntarily. 



The experiments of Woolsey and his associates 

 (479-481) have provided a detailed description of 

 representation of body parts within the supplementary 

 motor area in the monkey. The face and arin portions 

 of this area are in part on the free surface of the medial 

 aspect of the hemisphere, and trunk and leg repre- 

 sentations lie almost entirely on the dorsal bank of 

 the sulcus cinguli. The lower face is nearest the rim 

 of the hemisphere at the rostral end of the corpus 

 callosum. The upper face, ear, neck and back as far 

 as the tail are represented sequentially along the deep- 

 est part of the sulcus cinguli. Finger representations 

 lie at the edge of the hemisphere at the rostral limit 

 of the prccentral motor area, while more pro.ximal 

 parts of the arms are activated from points between 

 the finger area and the deeper parts of the sulcus 

 cinguli. Leg points extend back on the upper bank 

 of the sulcus cinguli with the proximal parts of the 

 limbs situated rostralK' and the digits caudally. 



Unilateral ablation of the supplementary motor 

 area in man does not produce a permanent impair- 

 ment of posture or movement (359, 360) but only a 

 transient and moderate hypertonia (360). Grasp re- 

 flexes follow unilateral or bilateral involvement (140). 

 Travis (426) describes in the monkey grasp reflexes 

 in the contralateral limbs after a unilateral lesion with 

 moderate hypertonia but no noticeable paresis. Since 

 after simultaneous bilateral ablation there is a greater 

 resistance to passive movement and contractures 

 have been seen (426), "supplementary motor area' 

 has been defined as a bilaterally functioning entity 

 concerned with posture and movement (358, 426). 

 Following bilateral ai)lation, no defect has been seen 

 in the ability to perform simple and complex prob- 

 lems despite the difficulties from hypertonus accom- 

 panying bilateral lesions (188). Hopping and placing 

 reactions are no longer present after a combined uni- 

 lateral ablation of the precentral and supplementary 

 motor areas (427). 



There is no agreement as to whether the supple- 

 mentary motor area acts directly, via fibers descending 

 in the pyramidal tract, or merely influences the ac- 



tivity of other cortical or subcortical centers, or Ijoth. 

 Movements have been described from stimulation of 

 the supplementary motor cortex after removal of the 

 precentral motor area and ahso in man after ablation 

 of both pre- and postcentral cortex (357). Moreover, 

 monopolar stimulation with single shocks in the sup- 

 plementary motor area of the monkey is said to evoke 

 a response of the pyramidal type (see Chapter 

 XXXIV in this work by Patton & Amassian) in both 

 ipsilateral and contralateral corticospinal tract (47). 

 However, anatomical studies have not disclo.sed any 

 degeneration of fibers in the spinal cord following 

 ablation of a large part of the supplementary motor 

 area, including resection of a point which yielded 

 movements of the lower limbs (121 ; De\'ito, J. L. & 

 O. A. Smith, personal communication). Although 

 these fibers descend in the internal capsule, the ma- 

 jority terminate in the pontine nuclei. A new series 

 of experiments in the light of these anatomical findings 

 has led to the conclusion that responses in the pyrami- 

 dal tract can no longer be recorded after removal of 

 area 4, if care is taken to prevent spread of stimulating 

 current (403). When this possibility is avoided and 

 area 4 is intact, it is found that the pyramidal tract 

 responses to supplementary motor area stimulation 

 have a longer latency than tho.se from direct stimula- 

 tion of area 4. This and other supporting evidence has 

 suggested that the activity froin the supplementary 

 area is relayed through area 4 (403). Indeed, a large 

 number of association fibers to this area has been ob- 

 served histologically (121). Additionally, area 6 and 

 the postcentral g>rus receive fibers from the sup- 

 plementary motor area of both hemispheres (121). 

 No projection to this area has been found from the 

 nucleus ventralis lateralis thalami (14). 



On the basis of these data, activation of area 4 

 through associational fibers, such as those from the 

 supplementary area, might give rise to quite differ- 

 ent patterns of mo\ement from those which arise when 

 the Rolandic motor strip is directly stimulated. It is 

 obvious, however, that the complexity of motor 

 patterns, including the homolateral movements ol)- 

 tained after hemispherectomy (41), must take into 

 account the involvement of other cortical and sub- 

 cortical structures which ma\' he implicated on the 

 basis of anatomical data cited al)o\'e. 



Second Somalia Area 



Following the demonstration of the existence of a 

 second sensory area by Adrian (10, 11), several studies 

 have extended the concept of a somatotopic repre- 



