Even for those of us navigationally challenged, we may have vivid memories of exactly where we once saw a bad accident or a deer on the side of the road. These negative experiences boost our recall of places, according to new research. As a result, the very places we may want to forget are the ones that we may remember most.
Researchers found that consistently associating negative imagery with specific locations activates a part of the brain – the parahippocampal cortex – that enhances memory of places during navigation. This enhanced recall appears to occur automatically, without people even being aware that the negative imagery is affecting their memories, and the researches say that, evolutionarily, this process serves as a cue for avoiding potential threats.
In the study, scientists in the lab of Jason Mattingley at the University of Queensland set up a virtual house in which a negative event occurred in each room. The events – represented by images from the International Affective Picture System library – were either positive, negative, or neutral in the emotions they sought to elicit and were unrelated to navigating through the house. The set of negative images included scenes of attack and threat, such as people brandishing guns at the viewer and a close-up view of an angry dog.
The researchers, led by Edgar Chan, varied when these events occurred, with some happening consistently and others changing in frequency. The day after navigating through the house, the participants viewed static images of the previously navigated house, but now without the emotional imagery, while in the MRI scanner.
When participants viewed a room in which they had previously encountered negatively arousing images, the researchers found significantly enhanced parahippocampal activity, as Chan and colleagues reported in the Journal of Cognitive Neuroscience. Jason Mattingley talked with CNS about his group’s findings and their significance for research on navigation and recall.
CNS: How did you get started in this line of research?
Mattingley: Our work on memory for places began as part of a larger project aimed at studying the mechanisms that underlie navigation in real and conceptual spaces. This was a multidisciplinary project, funded by the Australian Research Council, which brought together scientists working on navigation in insects, such as ants and honeybees, rodents and humans. Much of our research has been inspired by work on spatial memory and navigation in non-human species, and also by work on artificial systems for navigation in autonomous agents such as robots.
When we began our research, we were struck by how little was known about the contribution of affective states to memory for places. This seemed strange, given the subjective impression that our ability to recall a place we have visited is more vivid when something happened there to trigger a strong emotional response, such as a first date or bitter argument.
CNS: What do we know about how emotions affect both general recall and, specifically, place recall?
Mattingley: There is little doubt that emotions can affect our recall of previously encountered stimuli and events. Interestingly, however, while some studies have suggested that emotional processing enhances recall, others have found that emotionally charged events impair or distort our memory for people and events encountered. When it comes to memory for places, previous work has suggested that affective arousal enhances memory for the central element of an emotional event – such as being attacked by an angry dog – whereas memory for the scene context – such as a neighbor’s front yard – is more likely to be forgotten. Clearly, the manner in which emotion influences memory is highly complex and depends on many different factors.
CNS: Were you surprised by any of the results? If so, which ones
Mattingley: We had expected, based on previous research, that people’s memory for the rooms in our virtual environment might be influenced by both positive and negative emotional stimuli encountered during encoding. Participants indeed showed more efficient – faster – recall of object-location information for rooms associated with positive and negative stimuli than for the room associated with neutral stimuli.
But the brain imaging results told a different story. Specifically, we found that activity in the parahippocampal cortex during memory retrieval was significantly enhanced only for places associated with negative emotional events. By contrast, places associated with positive events elicited a neural response similar to that found with neutral stimuli.
We were also surprised that enhanced parahippocampal activity was only evident when rooms were consistently associated with negative stimuli. For rooms in which negative and neutral events were equally likely, the parahippocampal cortex no longer showed any differential response. Clearly, the certainty – or uncertainty – with which a place is associated with negative emotional experiences plays an important role in determining how it is recalled.
CNS: Can you highlight any unique aspects of the experimental design
Mattingley: There are two fairly unique aspects of our experimental design. First, during the initial learning phase of the study participants never actually saw positive or negative images while inside the virtual rooms. The images were always shown separately, right after participants completed their object-location response, to reduce the likelihood of simple visual associations between the affective images and the virtual rooms. Second, during the retrieval phase of the experiment, when participants underwent fMRI, they were never shown the affective images. Instead, they simply determined whether a line drawing belonged in a given room. By adopting this approach, we could be sure that any emotional influence on place memory arose from the initial learning phase of the study, and not from exposure to affective images in the scanner.
CNS: What is the significance of the enhanced parahippocampal response during recall?
Mattingley: Overall, our findings suggest that the parahippocampal cortex automatically ‘tags’ the emotional relevance of places we visit. Specifically, our results suggest that the parahippocampal cortex stores a richer or more elaborated representation of places that are consistently associated with the experience of negative emotional arousal. Interestingly, this effect may occur implicitly, as our participants remained unaware of the link between the rooms they visited and the affective images they encountered there.
CNS: How might these recall processes play out in real life?
Mattingley: Whether we remember a place, and how well we remember it, is not determined merely by an act of will; our emotional state during the encounter has a crucial role to play. This is especially true for negative experiences – an angry dog in a neighbor’s yard or a hairy spider in the bathroom. One unfortunate consequence is that the very places we might wish to forget are the ones that tend to loom large in our memory.
CNS: What distinguishes this study from past studies in the area?
Mattingley: We believe ours is the first study to have investigated, in humans, both the neural and behavioral effects of emotional arousal on spatial memory during active navigation.
CNS: What is next for this work?
Mattingley: In future work, we would like to dig deeper to determine whether there is a unique neural signature for places associated with positive emotional experiences. Anecdotal evidence suggests there should be, but our current study failed to uncover any change in parahippocampal activity during recall of places linked with positive emotions. Perhaps we will need to employ more potent stimuli, such as images that have strong personal relevance, such as pictures of one’s own friends and family. We would also like to investigate further how different levels of emotional arousal influence activity within navigation-related brain areas, and determine whether this might in turn exert an unconscious influence on navigation behavior.
The paper “Negative Emotional Experiences during Navigation Enhance Parahippocampal Activity during Recall of Place Information,” Edgar Chan, Oliver Baumann, Mark A. Bellgrove, Jason B. Mattingley, was published online in the Journal of Cognitive Neuroscience on August 28, 2013, and is forthcoming in print.
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