Ptsd Research Quarterly

In the systems approach to human memory, the mind/brain is assumed to be multifaceted, with semi-autonomous specialized subsystems operating in parallel. The component subsystems function to highlight their own parts of the representational tableau, which includes the phenomenological experience, the actions, the preferences, and the memories of the person. A number of component systems have been identified or hypothesized, each with its distinctive functions, representations (both in terms of modality and format), and operating principles. Within this systems view, the mind can be likened to a chamber orchestra: Each subsystem or instrument contributes its own special qualities to the melody and harmonies of mind, providing an unparalleled complexity and richness. The music may be altered when individual instruments are either muted or amplified. Similarly, depending on the response of the individual subsystems to factors such as stress (or other factors such as age, hormonal levels, and cognitive set), different aspects of human experience may be accentuated or silenced. While there are undoubtedly many subsystems that contribute to human experience, in this summary, we shall focus on two that are of fundamental importance for our understanding of human memory under acute stress. The first system we shall consider is the “cool” cognitive system; the second, the “hot” emotionalfear system. We proposed that the “cool” hippocampal memory system records, in an unemotional manner, well-elaborated autobiographical events, complete with their spatial-temporal context. In contrast, the “hot” amygdala system responds to unintegrated fragmentary fear-provoking features of events, which become hooked directly to fear responses. The hot system is direct, quick, highly emotional, inflexible, and fragmentary. The cool system is cognitive and complex, informationally neutral, subject to control processes, and integrated. Hot-system memories are stimulus-driven and entail a sense of reliving—more like simple responses (often fearful) than like recollections. Cool-system memories are narrative, recollective, and episodic. The person knows that the events occurred in his personal past, and there is no sense of reliving or of mistaking the memory for a current percept. Normally, encoding in the two systems is thought to operate in parallel, with the cool system encoding the contextual panorama and the hot system contributing a “highlighting” of the specifically fearprovoking (or emotional) aspects of the experience. One implication of this theory is that it provides a natural explanation for the often-observed phenomenon of weapon focus—the finding that people selectively attend to and remember threatening objects, such as weapons, to the detriment of more neutral objects in the scene. In addition, as Burke and colleagues (1992) have shown, they selectively encode (and show enhanced memory on) the aspects of a story that have emotional impact. Presumably the hot amygdala system contributes a special emphasis or highlighting to such objects and events. Christianson (1992) and Egeth (1994) have provided reviews of the literature on the experimental effects of emotion on eyewitness memory. One criticism of the experimental literature in this area is that experimental studies are irrelevant to understanding traumatic stress, since they are conducted under minimally stressful conditions, and that the kinds of situations studied in the laboratory are radically different from naturally occurring situations (Yuille & Cutshall, 1989). A converging literature is accumulating that points to the separability of a hot, amygdala-based, and a cool, hippocampus-based system. LeDoux (1995) and Davis (1992), having both conducted extensive research on the amygdala, have reviewed the neural circuitry underlying fear and anxiety, showing that lesions to the amygdala in rats eliminate the expression of fear and the ability of the animals to learn conditional fear. LeDoux argues that the fear-related function of the amygdala holds in all vertebrates, including humans. He has traced the informational pathways leading into and out of the amygdala by observing the results of selective lesions on fear conditioning. One pathway is a quick, uncognitive route, in which stimulation of the amygdala results directly from the thalamus. A second pathway is more circuitous and cognitive, and involves feedback from both the hippocampus and the cortex. Results indicate that once fear is conditioned, it is virtually indelible, although the connection to the frontal lobes and other cortical regions—parts of what are here called the cool sys☎