There is an overwhelming body of scientific literature describing the role that stress and anxiety can play in our physiological and psychological health. Chronic stress has been associated with a number of serious ailments, such as heart disease, along with a myriad of other potential disorders. The mechanics by which stress and anxiety affect health are not entirely understood; it appears that there are complex and interactive biological and psychosocial systems that affect each other, with stress sometimes being the cause of certain problems, while at other times being caused by similar events and circumstances. One area in which stress and anxiety intersect with physiological processes is in the formation and subsequent recall of memories. Exposure to stress or the experience of short-term and chronic stress can have a significant deleterious effect on the formation of certain types of memory; further, some evidence has shown that chronic conditions such as Post Traumatic Stress Disorder (PTSD) may not only affect the proper development and recall of memories, but may actually have a deleterious effect on brain structures. Interestingly, however, there are certain memory functions –such as the development of memories associated with social hierarchy- that may be enhanced or reinforced by concurrent stress and anxiety. In sum, stress and anxiety are often closely associated with memory, and this association is typically manifested in memory deficits and loss. The complex relationship between stress, anxiety, and memory dysfunction is built on both psychological and physiological processes, and significant advances have been made in recent years to further our understanding of this relationship.
Contemporary concepts about memory have their roots both in Freudian psychoanalysis and in biological medicine. Freud posited that maladaptive memory was associated with inherent pathology, largely dismissing a physiological role in memory formation (or, more specifically, in maladaptive memory formation) (Bremner, 1999). More recent studies have shown, however, that maladaptive memory formation can result from environmental causes, though these causes are typically associated with various physiological processes. There are a number of brain structures, such as the hippocampus and the amygdala, that have been shown to have an association with memory functions (Chattarji et al, 2009), and maladaptive memory processes have been seen to correlate with the dysfunction of these structures.
For decades, researchers largely discounted the role of environmental factors in the development of mental disorders, believing that physiological dysfunction, resulting from injury, genetics, disease, or other factors, was at the root of most or all such disorders (Bremner). It is only relatively recently that research has begun to uncover the intertwining links between environmental factors and physiological factors; more specifically, contemporary research has shown how environmental factors may in some cases actually cause physiological dysfunction (Hartley & Phelps, 2012). One such study examined the connection between patients with PTSD and the ability to properly develop and later recall memories. This study focused primarily on the hippocampus and its role in the development of memory.
Stress is considered to be a necessary and important component of memory formation; it “is critical to the stress response, for example in assessing potential threat during a life-threatening situation, as occurs with exposure to a predator” (Bremner). In properly adaptive circumstances, exposure to environmental stresses allows the subject to form the correct responses to danger, and to react appropriately during future encounters with the same, or similar, potential threats. The function of the hippocampus in the formation of memory involves the release and processing of a complex combination of hormones; in the proper balance, these hormones foster the development of adaptive, useful memories (Bremner). When the function of the hippocampus is compromised, however, it may be difficult for the subject to form memories, or the development of memories may be incongruent with the severity or seriousness of the actual threat.
What has come to light from such studies is that damage to the hippocampus may not only lead to maladaptive responses to stress and the formation of memory, but may also be caused by long-term or severe stress. Subjects with PTSD have shown a statistically significant rate of hippocampic dysfunction wherein the production of hormones is compromised. This dysfunction, as associated with memory problems, can manifest in several ways. The first of these is the way that the memories associated with PTSD may be amplified and overwhelming, a finding that is hardly surprising (LaGarde et al, 2010). Beyond that, however, the formation of subsequent memories can be significantly impaired; these memories can include not just those that are typically recalled at a conscious level, but also those associated with such things as motor functions (Bremner).
The findings of the study related to PTSD and the hippocampus suggest that it is the over-production of hormones that leads to the damage associated with memory dysfunction. Simply put, the stresses of traumatic events or circumstances can lead to the overproduction of stress-related hormones; this results in the stressful events being stored as powerful memories, while also damaging the hippocampus in a manner which affects the development of subsequent memories. Not all traumatic events will cause such damage, of course, and not all those with PTSD will experience memory problems in the future. It is clear, however, that an overabundance of stress-related hormones can lead to short-term and long-term memory problems, manifest both as memory deficits and as memories that are too easily recalled.
Not all stress-related memory functions are necessarily negative; as noted, the association of stress and memory allows subjects to respond appropriately to future threats. There are other associations between stress and memory that can be helpful as well. One such area is in the development of social hierarchy responses. Lab rats exposed to stresses while living in colony settings were seen to develop their understanding of social hierarchies within the colony at a faster rate than those who were not (Lordi et al, 2000). Male rats whose exposure to stress was limited to the potential posed by dominant males were likely to take longer to settle into roles of dominance and submission than were those who were exposed to an outside stressor (in this instance the threat was posed by exposure to a cat) (Lordi). Further, the correlation between stress and memory formation in lab rats was seen to be greater in males than in females (Bowman et al, 2009). This may have social implications, as the outside threat would seem to lead to a more rapid development of the social cohesion needed to effectively face such a threat.
The role of stress on memory is not just physiological; psychological response to stress can also lead to memory impairment. Subjects in one study who believed that memory loss is associated with memory were more likely to report memory loss, and even to demonstrate memory deficits on standard tests, than were those who did not associate age and memory loss (Report, 2010). The conclusions reached by researchers in this study were that the anxiety felt by the subjects who believed they were likely to develop memory deficits was a direct cause of the impairments seen in these subjects. In short, those who believed they were likely to develop memory deficits were more likely than the average person to actually develop such deficits. The deficits seen in this research were not associated with the sort of impairment seen in the hippocampus of some PTSD patients, and researchers concluded that such deficits were strictly a result of concurrent anxiety.
Stress and anxiety may not only affect a subject directly, but may also have multi-generational effects. Pregnant lab rats exposed to stresses during gestation have been shown to produce offspring whose memory functions, and even overall cognitive functions, are maladaptive (Lordi et al). This sort of memory dysfunction would seem to be a result of physiological processes, seemingly making it clear that memory deficits and dysfunction associated with stress and anxiety are not all the result of the same processes. In some instances, memory deficits associated with stress and anxiety may be a result of psychological dysfunction and an inability to cope with such stress; in other instances, long-term or chronic stress and anxiety may result in actual physiological damage to structures such as the hippocampus. These differences would seem to indicate that the responses to, and treatment of, such memory disorders would necessarily be different depending on the cause. It may not yet be clear how best to treat all of the various types of memory disorders associated with stress and anxiety, but contemporary research does appear to be pointing to more direct answers about where to begin looking for such treatments.
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Bowman, R. E., Micik, R., Gautreaux, C., Fernandez, L., & Luine, V. N. (2009). Sex-dependent changes in anxiety, memory, and monoamines following one week of stress. Physiology & Behavior, 97(1), 21-29.
Bremner, J. D. (1999). Does stress damage the brain? Biological Psychiatry, 45(7), 797-805.
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Report (2010). Worrying about memory loss can worsen memory problems: negative expectations about memory performance may actually indicate anxiety or depression. Mind, Mood & Memory, 6(6), 6.
Van der Kooij, M. A., & Sandi, C. (2012). Social memories in rodents: Methods, mechanisms and modulation by stress. Neuroscience & Biobehavioral Reviews, 36(7), 1763-1772.