SENSORIMOTOR CORTICAL ACTIVITIES 



813 



indicated in the maps of Bailey et al. (37). Function- 

 ally similar areas have been described in the cat (166) 

 and comparable points noted in the human brain 

 (168, 190, 347). 



The phenomenon of "suppression" was said to begin 

 several minutes after stimulation, depending upon 

 the depth of anesthesia and the distance of the stimu- 

 lated point from the motor cortex, and to persist as 

 long as 30 min. It was reported to be inconstant and 

 variable, and could not he elicited again for a con- 

 siderable period following the first response (cf. 122, 

 399). The postulated paths in this suppression were 

 said to involve a corticosubcorticocortical circuit 

 passing through the caudate nucleus (135). Cortico- 

 caudate connections were described by strychninog- 

 raphy^ (131, 169), and corticocaudate fibers (cf. 

 321-324) were said to arise in the suppressor areas 

 (176, 307) which, howe\er, were not found by other 

 authors (240, 433). Experimental findings indicated 

 also that stimulation of the caudate inhibited corti- 

 cally-induced moxements (cf. 308) as well as 

 depressed cortical electrical activity (174). 



Much of the data relating to the phenomenon of 

 'suppression' has been challenged or reinterpreted 

 (cf 122, 399J with the implication that this phenom- 

 enon mav not e.xist as a physiological mechanism. 

 Sloan & Jasper (399) have identified "suppression' 

 with the phenomenon of spreading depression which 

 is not restricted to specific cortical areas but is related 

 to experimental interferences (cf 122, 399).- In their 

 study, and in that of Druckman (122), the available 

 e\idences are reviewed with the conclusion that the 

 notion of 'suppressor areas' should l)C aijandoned. 

 Moreover, lesions of cortical and subcortical struc- 

 tures said to be inxohed in suppressor mechanisms 

 have not produced an increase in muscular tone as 

 would be expected in the concept of suppression. 

 These data ha\e been reviewed b\- Myers et al. (343). 



In more recent years, however, a region in the 

 superior temporal gyrus has been described as yielding 

 phenomena closely resembling suppression both in 

 man and monkey (152). While these results may 

 eventually point the way to future research, at present 

 it is obvious that the lability of cortical motor func- 

 tions, as exemplified by both the facilitatory and inhibi- 

 tory actions already discussed, suggests the existence 

 of cortical areas capable of exercising a broad influ- 

 ence on the initiation and progression of movement. 



- .\ comprehensive rev iew of literature relevant to spreading 

 depression has appeared (2893). 



Such a function appears to be significant in the supple- 

 mentary motor area, in area 24 and in the orbital 

 cortex, but other cortical areas may participate, as 

 suggested in particular ijy the studies of Tower (42 1 ) 

 and Hugelin & Bonvallet (213, 215) discussed below. 

 It is also interesting that reversal of the response to 

 cortical stimulation may follow either alteration in 

 stiinulus parameters or repetition of the stimulus, 

 although the mechanisms involved in this phenom- 

 enon are unknown. In this regard, it must be stressed 

 that interruption or arrest of a given function by 

 cortical stimulation, as in the arrest of speech or when 

 a movement cannot he performed by the subject 

 during the period of cortical stimulation (358), should 

 not necessarily be considered as proof of the existence 

 of an antagonistic action. Stimulation could merely 

 interrupt a patterning of neuronal activity necessary 

 for the performance of that particular function. 



Ablation Interfering with Total Motor Activity 



Hypokinesia follows lesions in inferior temporal 

 cortical areas (261). It is a marked feature of \entral 

 temporal resections in the baboon which in\olve 

 mainly the entorhinal area, and partially ablate the 

 hippocampus, but spare the amygdala on one or both 

 sides (3). Carey (77) has drawn attention to the 

 'great loathness to move' in monkeys with lesions in 

 the globus pallidus extending \entral from it and 

 involving pathways from the orbital and more 

 particularly from the temporal region. It may be 

 relevant that pathways from the entorhinal area also 

 traverse this region ventral to the globus pallidus in 

 the marsupial (6). Both arrest of movement and 

 automatic movements accompanying an amydgalo- 

 striatal interrelationship ha\e been reviewed recently 

 by Adey (4). See also CUiapter XXX\' by Jung & 

 Hassler in this work. 



Hyperkinesia, on the other hand, has been reported 

 following lesions of the posterior orbital cortex in the 

 primate with an increase in movement rates up to 600 

 per cent of that prior to operation (161). Certain 

 aspects of the ceaseless pacing seen in these animals 

 also accompany bilateral temporal lobectoin\- in the 

 monkey, and a re-examination of objects handled only 

 a few minutes previously may he repeated indefinitely 

 without apparent cognition. These findings suggest 

 that corticifugal influences from frontal and temporal 

 areas may play on common subcortical motor mecha- 

 nisms. 



