Rhawn Gabriel Joseph, Ph.D.
FEAR, RAGE & AGGRESSION
Initially, electrical stimulation of the amygdala produces sustained attention and orienting reactions. If the stimulation continues the subject may begin to experience, wariness, fear and/or rage (Cendes et al. 1994; Davis et al., 1997; Gloor 1992; Halgren 1992; LeDoux, 1996; Rosen & Schulkin, 1998; Ursin & Kaada, 1960). When fear follows the attention response, the pupils dilate and the subject will cringe, withdraw, and cower. This cowering reaction in turn may give way to extreme fear and/or panic such that the animal will attempt to take flight.
Among humans, the fear response is one of the most common manifestations of amygdaloid electrical stimulation and abnormal activation (Davis et al., 1997; Gloor, 1992, Halgren, 1992; LeDoux, 1996; Rosen & Schulkin, 1998). Moreover, unlike hypothalamic on/off emotional reactions, attention and fear reactions can last up to several minutes after the stimulation is withdrawn.
In addition to behavioral manifestations of heightened emotionality, amygdaloid stimulation can result in intense changes in emotional facial expression. This includes crying and facial contortions such as baring of the teeth, dilation of the pupils, widening or narrowing of the eye-lids, flaring of the nostrils, as well as sniffing, licking, and chewing (Anand & Dua, 1955; Ursin & Kaada, 1960). Indeed, some of the behavioral manifestations of a seizure in this vicinity (i.e. temporal lobe epilepsy) typically include throat and mouth movements, including chewing, smacking of the lips, licking, and swallowing–a consequence, perhaps of amygdala activation of the brainstem periaqueductal gray and nuclei subserving mastication.
In many instances patients or animals will react defensively and with anger, irritation, and rage which seems to gradually build up until finally the animal or human will attack (Egger & Flynn, 1963; Gunne & Lewander, 1966; Mark et al., 1972 Ursin & Kaada, 1960; Zbrozyna, 1963). Unlike hypothalamic “sham rage”, amygdaloid activation results in attacks directed at something real, or, in the absence of an actual stimulus, at something imaginary. There have been reported instances of patient’s suddenly lashing out and even attempting to attack those close by, while in the midst of a temporal lobe seizure (Saint-Hilaire et al., 1980), and/or attacking, kicking, and destroying furniture and other objects (Ashford et al., 1980).
Moreover, rage and attack will persist well beyond the termination of the electrical stimulation of the amygdala. In fact, the amygdala remains electrophysiologically active for long time periods even after a stimulus has been removed (be it external-perceptual, or internal-electrical) such that is appears to continue to process–in the abstract–information even when that information is no longer observable (O’Keefe & Bouma, 1969).