Stress/Memory

Stress/Memory

1. Sex Differences

   • Females
     • The observation of interacting influence of glucocorticoid and noradrenergic activation on subsequent intrusive memories in men but not women accords with previous findings of gender differences in associations between memory performance and stress hormones (Bryant)
       • Consistent with previous research, we found superior free recall of negative relative to neutral information [32,33]. This pattern was observed particularly in women who were exposed to High Stress at the time of memory consolidation. This pattern is also consistent with growing evidence of superior emotional memory in women, and the role of both stress and sex hormones in mediating emotional recal (Bryant)
   • Males
     • cortisol increase and emotional memory performance is observed in males, it is not found in females [16]. These relationships may not have been found in females because of variation of ovarian hormonal levels throughout the menstrual cycle (Bryant)
       • In men, the increase in cortisol following the arousal manipulation predicted better recall of neutral images (Bryant)
       • One unexpected finding was that men did not display enhanced recall after being exposed to the stressor; this is inconsistent with a number of findings of male participants displaying stress-related enhancement of emotional memories (Bryant)
         • One possible explanation is that the men in this study had elevated memory for the negative images in the warm water condition, with significantly greater recall of these images than women (Bryant)
       • The elevated recall of negative stimuli for men in the non-stressful condition may have reduced the possibility of a difference in recall scores between the stress and control conditions. (Branyt)
         • Experimental studies in animal models have also highlighted a link between early-life stress and markers of immune function in the central nervous system (CNS)—an apparently sexually dimorphic phenomenon with greater effect sizes in male animals (Danese)
   • Potential sex differences may exist in intrusive memories in men and women because of evidence that women have stronger retention for emotional memories [14,15]. Further, the role of glucocorticoids in intrusions may differ across gender [16]; further, there is evidence that the influence of cortisol on subsequent memory for emotional events is dependent on menstrual phase [17] [18]. There is evidence of differential glucocorticoid release across gender (Bryant)
     • In terms of men, free recall of neutral images was positively correlated with subsequent intrusions of neutral intrusions (r= .34, p= . 04). Conversely, women displayed a significant correlation between free recall of negative images and subsequent intrusions of negative intrusions (Bryant)

2. Oxidation

   • Underlying Mechanism involved in age, stress, and memory (Azmen)
   • Rats had low memory performance and higher Oxidative stress and compared to non-stressed rats (Azmen)
   • Exposure to long-term oxidative stress in brain tissue causes reduction in learning and memory (Azmen)
     • IN order to protect cells from Oxidative damage, aerobic metabolism generally depends on a stringent control of ROS by antioxidants
       • meta-analyses report dissociation between spatial and non-spatial working memory, wherein spatial working memory relies on a dorsal information stream whereas visual working memory relies on a ventral stream [49]. However, no differences were found in prefrontal cortex activity between spatial and non-spatial working memory tasks, making stimuli differences an unlikely explanation for our failure to replicate stress-induced N-Back working memory impairment (Giles)
     • Hippocampal morphology possibly secondary to reduction in brain oxidative stress and/or upregulation of BDNF concentration

3. Medical Consequences

   • Acute and Chronic stress from noise produces excessive free radicals that attach proteins, nucleic acids, and lipid membranes and disrupting cellular functions (Azmen)
     • Noise exposure is a stressful environment stimulus and has been shown to impair cognition such as acquisition of memory, consolidation, and recall (Azmen)
   • Stress associated with memory deficit (Azmen)
     • Stress experienced before, during, or following a period of learning can enhance or block memory formation depending on nature of stress (Dalesman)
       • When experienced together the stressors had an additive effect blocking all memory processes (Dalesman)
         • It is not always the same with multiple stressors because of the complexity of the sensory systems mediating each of the stressors and the fact that the intrinsic membrane property is not the only important variable tjat alters aerial respiratory behavior (Dalesman)
           • The intrinsic membrane properties of each of the neurons as well as the synaptic interactions between them will have to be examined in order to come to an understanding of how stressors when experienced together alter aerial respiration (Dalesmand)
             • The literature on stress effects on working memory is mixed. Several neuroimaging studies assessed the influence of stress on working memory-related brain activation (Giles)
               • stress impaired performance on active tasks that require constant updating of information (Giles)
           • Importantly,the lack of change (10 min) or depression (3 h and 24 h) in TBT also indicates that the lack of memory following exposure to PLOS ONE | www.plosone.org 9 combined stressors was not duetoanincreaseinbreathing behaviour masking memory during these time points. (Dalesman)
             • The human brain solves problems necessary for social, emotional, and academic success. The brain learns best with tasks that are challenging but not boring or overwhelming which is called “Just Manageable Difficulty (Brendtro)
           • ) encoded memories are not sufficiently embedded in one’s autobiographical memory base because of altered consolidation secondary to arousal (Bryant)
             • vents are encoded in fragmented and perceptually-based modes that lead to their subsequent intrusion into awareness (Bryant)
             • emories are unintentionally activated by internal or external triggers that were initially conditioned with encoded memory (Bra
             • oughts that are consistent with immediate and emotionally salient threats are more likely to intrude (Bryant)
       • he brain initially treats unfamiliar persons or stimuli as potentially threatening, sending a low level alarm of possible danger (Brendtro)
         • Prolonged alarm responses can alter the brain’s neural systems. Some pathways are strengthened (e.g., strike out, retreat). Others are weakened (e.g., stay calm, problem-solve). Brains rigidly organized in this way are less responsive to the environment (Brendtro)
   • Stressed rats possesed lower number of pyramidal neurons in the hippocampus as well as in the mPFC compared to non-stressed rats (Azmen)
     • t NGF administration improved learning and memory impairments in aged rats, coupled with partial reversal of cholinergic neuron atrophy (Azmen)
   • Stress is any condition that seriously perturbs the physiological or psychological homeostasis of an orgainsim (Dalesman)
     • Stress leads to alteration of the ability to form memory (Dalesman)
       • Danger produces distress (negative stress) activating painful emotions like fear and shame.(Brendtro)
         • The same stressful situation (e.g., bungee jumping) is interpreted differently by various individuals (Brendtro)
           • hether or not a challenging situation poses a threat depends on one’s coping strengths, past experiences, and state of mind and emotion. Humans also handle stress better when supported by others. (Brendtro)
             • The effects of psychological stress are physical as well, in that acute stress activates the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic nervous system (SNS), producing elevations in cortisol, alpha-amylase (AA), and heart rate (Giles)
               • Extensive experimental psychology research has attempted to parse the complex relationship between psychosocial stress, mood, cognitive performance, and physiological changes (Giles)
       • Opportunity produces eustress (positive stress) activating pleasurable emotions like curiosity and affection. (Brendtro)
         • Although these mediators are functional in eliminating the triggering stimuli, they can also exert neurotoxic effects and suppress neurogenesis (Hanisch and Kettenmann, 2007). T cells can potentiate the immune response to pathogens and amplify the inflammatory response, ultimately increasing neurotoxicity (Kipnis et al, 2012). Finally, cytokines can have neurotoxic effects (eg, by stimulating the production of reactive oxygen species), reduce monoamine transmission, potentiate glutamate transmission (and excitotoxicity), and inhibit neurogenesis (Miller and Raison, 2015). (Danese)
           • e brain is not immunologically separated from the peripheral immune system. In contrast, there are several pathways that ensure effective links between the peripheral immune system and the brain immune system (Danese)
           • On the one hand, signals from peripheral cytokines can be translated into CNS signals in several ways. Peripheral cytokines can stimulate afferent fibers of the vagus nerve, which in turn can trigger cytokine production within the brain. Peripheral cytokines can also cross into the brain where the blood–brain barrier (BBB) is permeable or leaky (eg, area postrema) and can be carried through the BBB saturable, active transporters. (Danese)
             • synapses that are in this way eliminated (Paolicelli et al, 2011). With regard to myelination, microglia exert an important role in the survival and functioning of oligodendrocytes and, thus, myelin production. Stressed oligodendrocytes can recruit microglia through secretion of chemokines, cytokines, and other mediators (Danese)
               • Because of the important roles that the immune system has in regulating key cellular events during the brain development, postnatal early-life immune activation involving disruption of these fine-tuned processes could exert direct, long-term influences on brain and behavior (Danese)
                 • Consistent with this prediction, experimental studies of infection (eg, influenza virus and Escherichia coli) and systemic inflammation (eg, synthetic RNA poly(I:C) and LPS) during prenatal or neonatal periods found stable, long-term impairments in cognition, including learning, memory, and attention in rodents (Danese)
                   • Working memory refers to the limited capacity system in which information is temporarily stored, updated, and maintained(Giles)
       • The Trier Social Stress Test (TSST) is the most commonly used method of experimentally inducing psychosocial stress, but it is resource intensive (Giles)
     • there is much evidence that arousal leads to better intentionally recalled emotional memories (Bryant)
   • Parts of Braing
     • The brain stem handles basic survival in all animals and is known as the reptilian brain. (Brendtro)
       • Because the brain is neither immunologically inert nor immunologically separated from the peripheral immune system, peripheral/ systemic immune activation exerts immediate effects on concurrent brain function, and in particular on domains (Research Domain Criteria; Insel, 2014) of cognition, (Danese)
         • peripheral administration of LPS decreases verbal and nonverbal memory in humans (Reichenberg et al, 2001). Peripheral administration of different pro-inflammatory mediators reduces ventral striatum responses to reward (Danese)
           • ore recent studies showed that stress can increase lymphocyte trafficking to the brain though expression of ICAM-1 by choroid plexus cells in rodents (Lewitus et al, 2008). Lymphocyte trafficking to the brain is likely protective in the face of stress (Danese)
             • wer anxiety levels and weaker acoustic startle response, and showed faster recovery to pre-stress hippocampal brain-derived neurotrophic factor (Danese)
             • hese protective effects are thought to be due to modulation of the stress-induced microglia activation by invading T cells and, thus, to reduction in secondary neuronal damage (Moalem et al, 1999; Yoles et al, 2001). Lymphocyte trafficking to the brain also generates memory T cells reactive to CNS antigens (likely signaling cellular damage under stress), which build immune memory and thereby boost secondary adaptive immune response and resilience in the face of subsequent stressors (Danese)
         • Peripheral administration of LPS potentiates amygdala activity in response to socially threatening stimuli (fear faces) (Inagaki et al, 2012), and typhoid vaccine reduces the connectivity of the subgenual anterior cingulate cortex (sACC) with the amygdala and increases the activity within the sACC during emotional face processing (Danese)
         • The immune system is also involved in activity-dependent mechanisms that regulate synaptic survival (Danese)
     • In mammals, the emotional or limbic brain is wrapped around the brain stem (Brendtro)
       • The amygdala (the Greek word means almond) in the emotional brain influences our likes and dislikes, thinking, memories, and social interactions with others (Brendtro)
         • brain’s danger and opportunity detector (Brendtro)
       • Psychological stress influences numerous psychological and physical processes in both healthy individuals and those with psychiatric disorders [1–3]. Stress is thought to influence mood [4, 5], memory [6], and decision-making (Giles)
         • Multiple studies have documented the influence of stress on hippocampal-dependent declarative memory, especially for emotionally arousing material (Giles)
     • In humans the higher prefrontal brain is highly developed to handle logical thought, language, and problem-solving. (brendtro)

4. Gene Expression

   • Different stressors can have similar effects on memory phenotype;, but effect central nervous system differently (Dalesman)
     • Makes it difficult to predict combing stressor effect on memory (Dalesman)
       • In real life, there are multiple stressors (Dalesman)
     • Previous work has shown that combining stressors with differing effects on phenotype may not alter memory formation in a predictable manner (Dalesman)
       • However, here stressors with a similar effect on phenotype (blocking LTM) appear to have an additive effect, i.e. blocking all memory processes, which may be due to the animal simply experiencing too much stress to pay attention to training. This was thought to be the reason why combining three different potential stressors, isolation, low calcium and predator kairomones, blocked the ability of Lymnaea to form LTM [5]. Alternatively, it may be specific to the type of stress experienced. (Dalesman)
         • The TSST is thought to be an effective method for inducing psychosocial stress, as it has repeatedly been found to increase anxiety, cortisol, and AA (Giles)
           • It also influences performance on a number of cognitive domains, including declarative memory (particularly for emotionally-arousing material), spatial, and working memory [14–16], as well as decision-making (Giles)
           • Both cortisol and AA increase following onset of acute stressors, however whereas cortisol levels peak at 10–30 minutes after cessation of stressor and take approximately 90 minutes to return to baseline, AA levels peak 5–10 minutes post-stressor and take only 10–15 minutes to return to baseline (Giles)
             • Therefore, it is not known how, exactly, the time course of changes in physiological indices of stress, such as cortisol and AA levels, relate to changes in mood and behavior (Giles)
           • tress influences memory through the release of cortisol, which binds to glucocorticoid (GC) receptors located in the hippocampus and prefrontal cortex (PFC), making these two regions particularly vulnerable to stress
       • Firstly, that the effect different stressors have may produce theame behavioural phenotype, but have different effects within the CNS (i.e. activity in RPeD1). (Dalesman)
         • we did not find stress effects on salivary alphaamylase (AA), a biomarker of autonomic nervous system activation

5. Plasticity

   • Physical and psychological stressors differ in their effects on certain neuronal plasticity-related genes (Dalesman)

6. Cortisol

   • Physical and psychological stressors produce differenes in plasma corticosterone levels (Dalesman)
     • Participants in the High Stress Condition displayed higher cortisol levels than those in Low Stress condition following the stressor manipulation. That is, participants in the High Stress condition experienced a greater increase in cortisol than those in the Low Stress condition immediately following the stress manipulation (Bryant)
       • Cortisol increase after the arousal manipulation predicted better recall of neutral memories in men accounting for 21% of the variance (see Table 4). In terms of negative intrusions for males, the only significant predictor was the interaction variable of increased cortisol and sAA, accounting for 16% of the variance; (Bryant)
   • Glucocorticoids have also been implicated in the modulation of emotional memories. For example, there is evidence that administration of hydrocortisone results in superior recall of subsequently presented emotional (rather than neutral) stimuli [11]. Increasing evidence suggests that the interaction of noradrenergic and glucocorticoid systems may underlie the superior recall of emotional memories [7]. It is proposed that glucocorticoid activation facilitates the noradrenergic cascade in the basolateral nucleus of the amygdala (BLA), thereby enhancing retention of emotional stimuli. (Bryant)
     • This finding is consistent with increasing evidence that it is the combined increase of noradrenaline and corticosteroid hormones that influence memory for emotional events (Bryant)
     • is proposeIt d that glucocorticoids pass the bloodbrain barrier readily, and thereby facilitate noradrenaline-mediated effects in the amygdala; this interaction of both glucocorticoid and noradrenergic activation may therefore contribute to the occurrence of subsequent intrusive memories of emotional experiences. The observation that negative intrusions were predicted by noradrenergic/glucocorticoid increase, but not by the stress manipulation alone, suggests that the individual variability in how participants respond to external stressors (such as cold water) plays an important role in the extent to which the stress response results in subsequent intrusive memories (Bryant)

7. Emotion

   • Stress triggers emotions which motivate behavior. Emotions activate changes in thinking, bodily function, and behavior. Our emotions prime us for specific patterns of coping behavior (brendtro)
   • There are highly traveled pathways going from the emotional brain to the survival brain which activate automatic flight and fight reactions. There are also many pathways from the emotional brain to the logical brain, which is why our emotions color our thinking (Brendtro)
     • The amygdala keeps a permanent reference of memories about events that brought extremes of emotion, such as fear or joy. This is why learning tied to positive emotions is more enduring. But vivid, terrifying events are also seared into our brain circuitry and cannot be forgotten (Brendtro)
     • With extreme emotion, the brain’s center for rational thinking shuts down (Brendtro)
       • Administration of propranolol reduces activation in the amygdala, as well as memory for emotional (but not neutral) material [9]. Further, memory for emotional, but not neutral, stimuli is associated with endogenous noradrenergic activation at the time of encoding [10] (Bryant)
     • The brain catalogues memories of important life events which is called episodic memory. Once these episodes are archived in memory, they are preserved unless reprogrammed by the verbal brain. Among the most significant contributions an adult can make is to help a youth gain new perspectives on important life events, including those causing pain. (Brendtro)
       • Intense emotional experiences, both pleasurable and painful, are etched, perhaps indelibly, in a child’s emotional storehouse (Brendtro)
         • hese children have tremendous capacity for positive growth and development, but trauma can stunt their ability to reach their potentials (Brendtro)
           • f painful memories are triggered by new situations, the brain acts as before, replaying the past or using defensive strategies to avoid further pain (Brendtro)
             • In accord with one previous finding, we noted that intrusive memories were more likely to occur following consolidation of negative, rather than neutral, stimuli [13]. Importantly, we found this pattern was greater when participants experienced stress (Bryant)
               • This interaction suggests that the level of stress attached to an emotional event at the time of consolidation contributes to the subsequent occurrence of intrusions. (Bryant)
                 • It also accords with findings of strongest amygdala recruitment when combining yohimbine and hydrocortisone [27], as well as the interactive effect of these agents on hippocampal activation during encoding of emotional material (Bryant)
               • arousal at the time of aversive experiences results in enhanced consolidation of these memories, which may contribute to these memories intrusively and unintentionally being retrieved (Bryant)
               • stress plays a critical role in the development of intrusive memories (Bryant)
                 • or example, compared to individuals without a history of childhood trauma, those with a history of childhood trauma have greater inflammatory response to subsequent stressors including experimental psychosocial stressors and daily stressors (Danese)
                   • Furthermore, early-life immune activation has been linked to greater neuroendocrine activation in the context of subsequent stressors (Danese)
               • this study provides the first evidence of the role of stress hormones at the time of consolidation on development of subsequent intrusive memories (Byant)
           • children traumatized by neglect and abuse overuse more primitive brain systems. Their survival brains are chronically stimulated, (Brendtro)
             • Similarly, administration of pro-inflammatory compounds in humans can induce cardinal mood symptoms (Danese)
               • Additional experimental support for the role of inflammation in the pathophysiology of affective disorders comes from the evidence of anti-depressant effects of antiinflammatory medications (Danese)
                 • In addition to sensitizing the immune system (glial priming), early-life immune activation can also cross-sensitize the neuroendocrine response to stress (Danese)
                   • For example, earlylife immune activation is associated with impaired neurogenesis and cognition (Danese)
                   • imilarly, childhood trauma is linked to impaired cognition (Danese)
                     • Evidence that childhood trauma and inflammation have synergistic effects suggests that both factors are likely to be on the same causative pathways influencing brain and behavior (Danese)
           • experimental animal models have shown that early-life stress can affect later immune functioning, but observational human studies are needed to test if childhood trauma does affect later immune functioning in ordinary people (Danese)
             • childhood trauma is a broad term encompassing various experiences ranging from child sexual abuse, to parental loss, and road traffic accidents. However, different types of trauma may have different correlates and consequences (Danese)
   • A person can remain highly stressed for hours after the end of an angry conflict (Brendtro)
     • Although intrusive memories are more likely to occur when the memory is emotionally charged [13], intrusive memories may function differently from intentionally retrieved memories (Bryant)
   • PTSD
     • Basically, something went wrong in the developmental process which had a damaging effect on emotional and behavioral adjustment. In trauma, some highly distressing experience produces very painful feelings, and the individual adopts defensive coping behaviors to protect against a recurrence (Brendtro)
     • such as attempts to suppress the memories or attributions made about the memories, which may influence the occurrence of intrusive memories (bryant)
     • Individuals who develop post-traumatic stress disorder (PTSD) also show elevated inflammation levels (Danese)
       • studies suggest that inflammation is a preexisting vulnerability factor for the development of PTSD in trauma-exposed individuals rather than simply a correlate of subjective distress, disease severity, or maladaptive coping strategies following PTSD onset (Danese)

8. Psychoneuroimmunology

   • The brain and the immune system are not fully formed at birth, but rather continue to mature in response to the postnatal environment. The two-way interaction between the brain and the immune system makes it possible for childhood psychosocial stressors to affect immune system development, which in turn can affect brain development and its long-term functioning (Danese)
     • they both emerge from fetal life with a minimal set of functions that enable newborns’ adaptation to a limited number of expected stimuli (Danese)
       • flammation appears to have trans-diagnostic effects on the brain likely resulting from the effect of inflammation on basic brain processe (Danese)
         • In contrast, inflammation is in many cases seen as a trait marker of vulnerability (Danese)
       • brain function, the effects of early immune activation on brain development, the sensitization of immune brain cells to subsequent psychosocial stressors (Danese)
         • The activity of the brain immune system contributes to normal brain functioning (Danese)
           • it is possible that similar immuno-modulatory interventions could improve treatment of psychiatric patients with a history of childhood trauma (Danese)
             • Childhood trauma identifies a subgroup of psychiatric patients who respond poorly to treatment and—possibly because of this—have unfavorable course of illness (Danese)
             • Childhood trauma also identifies a subgroup of psychiatric patients with elevated inflammation levels (Danese)
     • Experimental studies in animal models have also highlighted a link between early-life stress and markers of immune function in the central nervous system (Danese)
       • Of note, early-life stress also appears to be associated with greater reactivity to subsequent psychosocial and immune challenges (Danese)
         • it is possible that resilience to stress might be boosted by harnessing the adaptive immune system (Danese)
   • Hennessy et al, 2010a; Shanks and Lightman, 2001). Manipulation of stress exposure in early life (ie, across postnatal days 1–20 in rodents) has been undertaken through multiple experimental models previously linked to heterogeneous effects on mothers' caregiving behavior and stress reactivity, including neonatal handling, maternal separation, maternal deprivation, nursery rearing, early weaning, and dexamethasone treatment. (Danese)
     • maternal separation was found to be associated with blunted expression of pro-inflammatory mediators (lipopolysaccharide-binding protein) in the hippocampus (Danese)
       • maternal separation was associated with greater synaptic levels of the receptor (Danese)
         • Of note, elevated inflammation levels are observed not only after maltreatment by adults, but also after other common and severe childhood stressors, such as bullying by peers (Danese)
       • or example, rodents exposed to maternal separation showed a greater increase in core temperature upon a second separation (Hennessy et al, 2010b), greater cytokine expression in response to subsequent viral infection (Avitsur et al, 2006), and greater cortical microglial activation following subsequent exposure to chronic foodrestriction stress (Danese)
   • Initial evidence of links between the immune system and psychopathology, and particularly affective disorders, came from the recognition that animals and humans with acute infectious diseases developed a stereotypical pattern of behaviors characterized by lethargy, despair, anorexia, and reduction in grooming (Danese)