1406 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



FIG. b. Salivation and posture of defecation elicited by 

 amygdaloid stimulation in the cat. [From Anand & Dua (13).] 



Information in regard to other endocrine glands 

 is scanty. An increase in blood sugar concentration 

 is sometimes noted after amygdaloid stimulation 

 and thought to be evidence for epinephrine discharge 

 (11, 14). Occasionally the opposite is seen, suggesting 

 activation of insulin secretion (14). Recently, Mason 

 ( 1 78) has observed that amygdaloid stimulation 

 produces unmistakaljle signs of ACTH release Ijy the 

 pituitary gland. 



Integrated Behavioral Responses and Psyc/iic Phenomena 



FEEDING BEHAVIOR. Sniffing, oftcn along the floor, 

 together with searching movements are common 

 effects of amygdaloid stimulation (11, 72, 87, 88, i3;3, 

 135, 155, 168, 172, 175, 190). Repeated short amygda- 

 loid stimulations may induce increased nuzzling, 

 sniffing and licking for one or se\eral days (9). After 

 amygdaloid stimulation, food is eaten avidly {72). 

 However there seems to be no increase in the amount 

 of food intake (11, 13, 50). 



ATTENTION, FEAR .\ND RAGE. The most cominon be- 

 havioral responses elicited by stimulation of the 

 amygdala are reactions of attention, fear and rage 

 (11, 13, 51, 72, 82, 87, 88, 135, 155, 168, 172, 175, 

 186, 187, 190, 245), three types of behavior which 

 apparently are closely interrelated since, upon in- 

 creasing the intensity of stimulation, attention will 

 merge into fear and finally lead to rage (72). In man, 

 fear is occasionally, and rage only rarely elicited by 



amygdaloid stimulation (41, iii, 129). The attentive 

 response is associated with arrest of ongoing behavior 

 and with the usual somatomotor and autonomic 

 changes attending a normal attentive response of the 

 animal. The same principle holds for fear and rage 

 which also are accompanied by the typical postural 

 and autonomic changes correlated with these forms 

 of behavior. The rage reaction may lead to an attack 

 which may be well directed (172) or not (88). 



Gastaut and co-workers (88) pointed out that the 

 sequence of attention, fear and rage corresponds 

 closely to Pavlov's (196) 'orienting reflex" and to its 

 modifications occurring with increasing intensity of 

 the alerting stimulus. The vegetative changes at- 

 tending this Pa\lo\ian orientation response are also 

 quite similar to those observed on amygdaloid stim- 

 ulation (210). 



It seems worthy of note that on a few occasions 

 amygdaloid stimulation in animals was seen to pro- 

 duce quite an opposite, quieting effect sometimes 

 leading even to sleep (11, 13). 



REW.-kRDiNG EXPERIENCES. Amygdaloid stimulation 

 in awake unrestrained rats may induce a behavior 

 suggesting that such stimulation may produce an 

 'experience' which acts as a reward (192-194). This 

 was seen in experiments in which rats were able to 

 stimulate their own brain by pressing down a bar, 

 thus closing the stimulation circuit connected to the 

 electrodes implanted in the animal's brain. A delay 

 switch turned off the stimulation after a few seconds 

 and the animal had to release the bar and press down 

 again to receive another stimulation. The time the 

 animal spends bar-pressing serves as an index of the 

 rewarding character of the stimulation. In such an 

 experimental situation the amygdala, together with 

 the septum, gives the highest .scores, indicating that 

 stimulation of these areas is experienced as a reward; 

 this type of reward can even be used instead of food to 

 improve the rat's performance in rimnina; through a 

 runway. 



SEXUAL BEHAVIOR. Occasionally behavioral responses 

 suggesting sexual excitement may be observed in 

 female cats upon amygdaloid stimulation (72). 



MODIFICATIONS OF LEVEL OF AWARENESS, CONFUSION 

 AND INTERFERENCE WITH MEMORY RECORDING MECHA- 

 NISMS. Amygdaloid stimulation in man frequently 

 produces confusion, disturbances of awareness, un- 

 responsi\eness and amnesia for all events taking 



