In an interesting extrapolation to psychopathol-ogy, McNaughton and Gray attribute GAD to excessive output from the SHS. Underscoring the information processing aspects of the SHS, they describe GAD as primarily a cognitive disorder that involves an excessive perception of threat and a subsequent suppression of approach and excessive avoidance of threat. In contrast, the fight/ flight system (which has a greater involvement of the amygdala/fear system) mediates panic attacks (Gray, 1987, p. 366).
Gray's BIS theory readily accounts for the association between anxiety, on the one hand, and such characteristics as shyness, social withdrawal, sensitivity to punishments, a tendency to be easily discouraged, and a failure to develop active means of coping with situations, on the other hand—a dimension of internalizing disorders identified in multivariate studies of children (Achenbach & McConaughy, 1997; Quay, 1986). These are the characteristics to be expected in an individual in whom the balance between the BIS and the BAS has shifted heavily toward dominance of the BIS. The more reactive BIS would generate anxiety in situations that are only moderately threatening. On the assumption that other people dispense both rewards and punishments, much social interaction can be seen as involving an approach-avoidance conflict. The dominance of the BIS over the BAS would, in this case, result in passive avoidance (shyness and social withdrawal). Similarly, the dominance of passive avoidance in conflict situations would impede the development of active coping skills. Finally, the dominance of the BIS in extinction situations would produce more rapid extinction that is manifested as a tendency to become easily discouraged and to give up when pursuing goals. Therefore, this cluster of characteristics can be seen as a consequence of a temperament in which the BIS is strongly dominant.
To more clearly assess application to anxiety disorders, it is useful to consider Barlow's (1988) theoretical analysis. Barlow distinguishes between two types of anxiety, which he calls anxiety and fear. More completely, anxiety is termed anxious apprehension, whereas fear is an alarm reaction. Anxious apprehension refers to a process of anticipatory anxiety that helps to prepare the organism to cope with the challenges and stresses of everyday life, and this process (in extreme form) underlies GAD. At pathological levels, anxious apprehension is said to consist of a diffuse cognitive-affective structure that has the following components: (1) negative affect, (2) high arousal, (3) perceptions of helplessness or uncontrolla-bility of future events, and (4) "worry" or the allocation of attention to negatively valenced self-evaluative concerns and/or the autonomic correlates of the arousal itself.
Although Barlow's (1988) "anxiety" and Gray's BIS are not identical, there is enough overlap to argue that similar constructs are involved (Fowles, 1992a). Barlow's emphasis on preparation for stresses and challenges is entirely consistent with the role of the BIS in approach-avoidance conflict situations and situations involving frustration (failure) and with Gray's (1987, p. 263) comment that it prepares the organism for vigorous activity. Both anxiety systems, it is assumed, produce an increase in arousal. Barlow's emphasis on "worry"
can be seen in Gray's (1982, p. 13) comment that the BIS allocates attention to "the maximum possible analysis of current environmental stimuli, especially novel ones'' and his (1987, p. 263) description of the BIS as the "stop, look, and listen'' system. Further, the conclusion, cited before from McNaughton and Gray (1999), that excessive output from the SHS is involved in the etiology of GAD underscores the similarity of Barlow's anxiety systems and Gray's BIS. Because the BIS is responding to potential threats (including uncertain threats in the form of novelty), it is reasonable to see that this vigilant anticipation and appraisal of threats involve worry. More recently, Barlow and Durand (1995, p. 157) comment that the BIS ''seems heavily involved in anxiety'' and agree that "Gray's thinking is very close to'' Barlow's (1988) theory of anxiety and anxiety disorders. Overall, then, the two theoretical constructs share enough features that it can be proposed that Gray's behavioral inhibition system is involved in the etiology of GAD.
Returning to Barlow's (1988) theory, fear is modeled on Cannon's fight or flight response and is seen as a massive alarm reaction to potentially life-threatening situations. Panic attacks are viewed as alarm reactions, albeit false alarms in the sense that they are not based on objectively life-threatening situations. Panic attacks seen in the clinic include a fear of dying or losing control, as well as acute anxiety accompanied by somatic symptoms.
Citing evidence that false alarm panics are common in the population, Barlow suggests that they may serve as ««conditioned stimuli for classical conditioning, leading to further conditioned panic attacks, which Barlow calls learned alarms. Because patients with Panic Disorder focus strongly on their internal physiological cues, both Barlow (1988) and Mineka (1985) suggest that interocep-tive conditioning is involved, in which internal physiological cues become conditioned stimuli for panic attacks. What brings patients with Panic Disorder to the clinic, however, is not just the occurrence of panic attacks, but rather their anxiety over possible future uncued panic attacks. Whereas many individuals are not disabled by learned and/or unlearned panic attacks, Barlow suggests that those who become anxiously apprehensive about future attacks are disabled and seek treatment, that is, the same process of anxiety seen in GAD is proposed as a core feature of Panic Disorder. This line of reasoning is supported by the finding that patients with Panic Disorder almost always also meet the criteria for GAD.
Both Barlow's alarm reaction and Gray's fight/ flight system are modeled after Cannon's fight or flight response. Further, Barlow (Barlow and Durand, 1995, p. 157) cites Gray's fight/flight system as the basis for panic attacks and, as noted above, Gray (1987) relates the fight/flight system to panic attacks. Consequently, panic disorder can be seen as a strong response in Gray's fight/flight system combined with higher levels of activation of the BIS (producing worry and anxious apprehension). That is, Gray's motivational theory describes neurobehavioral systems that are involved in the major anxiety disorders.
Finally, the perception that alarm reactions and/ or negative events are neither predictable nor controllable is a risk factor for anxious apprehension in Barlow's theory (see also Mineka, 1985). This perception can be seen as related to the expectancies of response-contingent reward or relieving nonpunishment associated with activation of the BAS. Positive expectancies reduce the perceived threats of frustrative nonreward (failure) and punishment and, thereby, reduce input to the BIS, whereas activation of the BAS has a direct inhibitory effect on the BIS. In contrast, negative expectations will have the opposite effects.
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