1230 



HANDBOOK OF PH^■SIOLOGV 



NEUROPHVSIOLOGY II 



PER CENT 



COPULATING 



100 



1-9 10-19 20-29 30-39 40-49 60-59 60-69 70-73 



PER CENT OF CORTEX REMOVED 



FIG. 3. Effects of partial decortication on scn behavior in 

 male rats; per cent of animals in each lesion group continuing 

 to copulate after operation. [From Beach (8).] 



stroyed, without eliminating estrous i^ehavior in 

 response to estrogen. The female rabbit still mates 

 after removal of the neocortex, the rhinencephalic 

 cortex, and the distance receptors of olfaction, vision 

 and audition, the olfactory bulbs, eyes and cochlea, 

 respectively (i8). Davis (20) found that removal of 

 the whole neocortex in the rat did not interfere with 

 estrous cycles, mating, pregnancy or delivery, find- 

 ings which have been repeatedly confirmed (11). 



The cortex is essential for the initiation of mating 

 behavior in most male mammals. In the rat. Beach 

 (8) showed that while removal of 20 per cent of the 

 cortex did not reduce the percentage of males showing 

 copulatory behavior, no male mated if more than 60 

 per cent of its cortex had been destroyed (fig. 3). 

 Similarly, mounting behavior is lost in female rats on 

 decortication whereas their female patterns of ac- 

 tivity are retained (9). In these studies the location 

 of the cortical area removed was considered less im- 

 portant than the quantity. 



In the male rabbit (18, go) the destruction of 



neither the neocortex nor the olfactory bulbs alone 

 prevents courtship and mating activities, but the re- 

 moval of both olfaction and cortical representation 

 of somesthetic, auditory and visual sensibility ter- 

 minates sex behavior. 



Beach and his colleagues (35) have recently studied 

 in great detail the effects of decortication on repro- 

 ductive behavior in the male cat. In this species, in 

 contrast to the rat, large cortical lesions do not appear 

 to depress the animal's interest in the female so much 

 as they interfere with motor activity related to copu- 

 lation. Cats with large frontal lesions would attempt 

 to copulate Ijut would fail to uain intromission in most 

 cases. 



The results of decortication experiments reveal 

 that the loss of cortical sensory and motor areas 

 affects male sex behavior patterns more acutely than 

 it does the female activities. In each case the actual 

 execution of mating behavior appears to be controlled 

 by subcortical mechanisms. 



A type of rhinencephalic control over sexual be- 

 havior, especially in the male, has recently been re- 

 ported by several investigators. Hypersexuality in the 

 male monkey as a result of removal of the temporal 

 lobes was described by Kliiver and Bucy in 1939 (56). 

 Schreiner & Kling induced hypersexuality in the cat, 

 agouti, monkey and lynx by removal of the amygdala 

 and the overlying piriform cortex and demonstrated 

 its dependence on the male sex hormone (82-84). 

 Similar changes have been reported in man (76, 91). 



Green rt al. (41) have made a careful study of 

 experimental hypersexuality in the cat, observing the 

 effects of small electrolytic and surgical lesions in the 

 amygdala, hippocampus, piriform cortex and stria 

 terminalis. They were unable to produce hypersex- 

 uality by destruction of the amygdala alone; but 

 small lesions in the piriform corte.x, restricted to an 

 area just medial to the rhinal fissure and beneath the 

 basolateral amygdaloid nucleus, induced hypersexual 

 changes without damage to the amygdala (fig. 4). 

 The cats with such lesions were active and alert and 

 would mate in a strange territory, a procedure not 

 commonly practiced by apparently hypersexual cats 

 without lesions. Castration slowly reduced the hyper- 

 sexuality, but it could be restored with either androgen 

 or estrogen. 



Hypersexuality was not observed in female cats 

 with amygdala-piriform-cortex lesions by Schreiner & 

 Kling (82-84) or Green ei al. (41). Gastaut (33) de- 

 scribed estrous activity in cats with rhinencephalic 

 lesions in which the reproductive tract appeared 

 anestrous. Female rabbits with lesions in the septum, 



