Suarez Jimenez, B;
(2016)
The Role of Spatial Location in Threat Memory: Modulation of Learning and Discrimination.
Doctoral thesis , UCL (University College London).
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Abstract
Learning about dangers in our environment is a vital adaptive behavior, and many have studied the association of environmental cues with danger or safety. However, the outcome associated with a specific environmental cue can depend on where it is encountered, and relatively little is known about the neural mechanisms behind location-specific threat learning within a single environment. Through a series of experiments, I developed a novel virtual reality task comprised of safe and dangerous zones within a single environment. Healthy volunteers explored this environment while ‘picking flowers’, which they were told might contain bees. On contacting a flower, participants were frozen for a short period of time and, if ‘stung,’ received a mild electric shock at the end of this period. Participants had the opportunity to learn that bees only inhabited flowers in one ‘dangerous’ half of the environment. Participants were able to discriminate zones that predict safety and threat within a single environment, with galvanic skin responses and subjective reports increasing as they approached and picked flowers in the dangerous half of the environment. Using functional magnetic resonance imaging, I found posterior medial temporal lobe structures (parahippocampus, posterior hippocampus) to be involved in memory for object locations. In contrast, anterior hippocampus, amygdala, and ventromedial prefrontal cortex showed greater activity when approaching flowers, but this activity did not differentiate between safe and dangerous zones. However, once participants reached a flower in the dangerous zone, increased activity was seen in areas associated with imminent threat, such as the midbrain/periaqueductal gray, dorsal anterior cingulate, and insula cortices. These results are the first to reveal mechanisms of location-specific threat learning in humans, in the absence of obvious boundaries delineating safety and danger zones. In the future, I hope this new paradigm will be used to understand the overgeneralization of threat in anxiety disorders and post-traumatic stress disorder.
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