It’s nearly mid-October here at Tufts, and the lazy days of summer seem to drift further into memory as us students find ourselves increasingly bombarded with exams, interviews, projects—you name it. As someone prone to worry and obsess, I find myself often in a high state of arousal. Arousing stimuli constantly factor into our lives, influencing and shaping not just our affective states, but also cognitive processes like memory. With specific regard to memory, research suggests that arousing events alter both what we remember, as well as how we remember. Neuroscience research has explored and shed light on the brain regions and neural pathways that may explain the modulatory effects of arousal on memory.
Arousal has been shown to affect what aspects of stimulus information we remember, although much remains equivocal. Some research points to arousal heightening memory for central details at the cost of memory for peripheral details. Christianson & Loftus (1991) conducted a study in which participants viewed a series of slides. One critical slide in the middle of the series differed by group in that it was either arousal-provoking (a woman injured near a bicycle), or emotionally neutral (a woman riding a bicycle). The researchers found that subjects who viewed the series that contained the arousal-provoking slide were more likely to remember central details (i.e. details about the injured woman, such as the color of her clothing) of the image than peripheral details (i.e. details about the surrounding scene the woman was in), while subjects who viewed the series with the neutral slide were more likely to remember peripheral details than central details.
However, as Laney et al. (2004) point out, the scientific community must take caution when generalizing such findings. They argue that the arousing stimuli used in laboratory experiments often are strong negative visual stimuli, which may not accurately reflect the arousing stimuli people face in their everyday lives. They draw a distinction between the aforementioned visual stimuli, which may have served as “attention magnets”, and a different kind of arousal—thematically induced arousal. In this latter kind of arousal, the arousing stimuli are not necessarily singularly arousing visual images, but rather events that may be more subtle, less abrupt, and perhaps more sustainable. The researchers performed an experiment where participants were exposed to one of two narratives. The first was emotionally neutral and involved a story about an average day in the life of a college student, while the other was an analogous story that contained the same subject, but in this case the subject suffered from depression, failing grades, and suicidal thoughts. The researchers found no evidence of memory narrowing for central details in the arousing stimuli group, as they were able to recall peripheral information just as well as the control group. This result is as odds with the one previously suggested by Christianson & Loftus (1991), and suggests researchers must be careful in the ways they characterize and define arousal.
How does arousal act on memory consolidation on a neural level? Experts agree that the medial temporal lobe—which houses important structures implicated in memory consolidation, including the hippocampus and amygdala—is critical specifically for arousal-mediated memory consolidation. Rather than act as a “permanent site” of plastic changes resulting from memory consolidation, which Packard et al. (1994) showed is not the case in nonhuman subjects, research supports the idea that the amygdala plays a selective role in memory consolidation within the hippocampus through both direct and indirect pathways. In one study that sought to examine the importance of interactive amygdalo-hippocampal processes in memory consolidation, researchers compared memory for arousal-inducing vs. neutral words in unilateral temporal lobectomy patients and control subjects (LaBar & Phelps, 1998). Both control subjects and lobectomy subjects demonstrated heightened arousal at the time of encoding (as measured by skin conductance responses). However, with regard to recall of arousing words at the time of encoding (immediately following the experiment) as compared to recall one hour later, only control subjects showed increased memory of words. Both groups showed decreased memory for neutral words. These results seem to suggest that arousal acts on consolidation, and further, that the medial temporal lobe is critical for this consolidation process.
Arousal may mediate memory consolidation not just through direct neural pathways, but also through indirect hormonal connections. Cahill et al. (1994) suggested the important role of arousal-related hormones such as epinephrine and norepinephrine (as well as the role of their receptors) in remembering arousing information. In subjects who received a β-adrenergic receptor antagonist, propranolol hydrochloride, memory for an emotionally arousing narrative was significantly impaired, while memory for an emotionally neutral narrative was not impaired. This implies that activation of β-adrenergic systems is critical specifically for the encoding of arousing information and not essential for encoding of emotionally neutral information.
While neuroscience and cognitive psychology has made great headway in the study of arousal and its modulatory relationship on memory, it’s important to bear in mind that there are different ways of characterizing arousal, which in turn may have different implications on memory. In addition, on a neural level, there are different mechanisms, from synaptic connections of critical brain regions to hormonal regulation that play a role in the effect of arousal on memory formation and consolidation. All of these relationships and nuances are important to consider as more research is done.
Cahill, L., Prins, B., Weber, M., McGaugh, J. L. (1994). β-Adrenergic activation and memory for emotional events. Nature, 371, 702-704.
Christianson, S., Loftus, E.F. (1991). Remembering emotional events: the fate of detailed information. Cognition and Emotion, 5, 81-108.
LaBar, K.S., Phelps, E.A. (1998). Arousal-mediated memory consolidation: role of the medial temporal lobe in humans. Psychological Science, 9, 409-413.
Laney, C., Campbell, H.V., Heuer, F., Reisberg, D. (2004). Memory for thematically arousing events. Memory & Cognition, 32, 1149-1159.
Packard, M.G., Cahill, L., McGaugh, J.L. (1994). Amygdala modulation of hippocampal-dependent and caudate nucleus-dependent memory processes, Proceedings of the National Academy of the Sciences, 91, 8477-8491.