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Keywords:

  • adrenergic system;
  • emotional memory;
  • heart rate;
  • intrusive recollection;
  • PTSD

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGMENTS
  8. REFERENCES

Abstract  Considerable evidence suggests that the adrenergic system plays an important role in the biological mechanism of post-traumatic stress disorder (PTSD). In the present pilot study the association between heart rate (HR) recorded prior to slide viewing and long-term emotional memory was compared between human subjects with a past history of PTSD (n = 6) and healthy women controls (n = 12). The correlation between HR during the anticipatory period and emotional memory was significant for the PTSD group (r = 0.93, P < 0.001) but not for the control group (r = 0.21, NS). The adrenergic reaction appears to be associated with emotional memory, which may be strengthened in subjects with a past history of PTSD.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGMENTS
  8. REFERENCES

Prior trauma is one of the important risk factors in post-traumatic stress disorder (PTSD).1 The mechanism of the association has not yet been directly investigated, but a past history of PTSD would be a sensitizing factor for a new traumatic event. Because the experience of a stressful event might be accompanied by epinephrine release, the adrenergic system may play an important role in the enhanced encoding of trauma-related memories of PTSD patients.2

A previous study demonstrated that declarative memory for an emotional event was enhanced by post-learning epinephrine infusion.3 That study indicated that an activated adrenergic system was associated with heart rate (HR) during or after slide viewing, while the possibility that ‘priming’ arousal may influence the enhanced memory was suggested.3,4

To our knowledge, the relationship between an anticipatory arousal measured by HR and long-term memory of emotional events has not been investigated in drug-naïve human subjects. The aim of the present pilot study was to examine the relationship between enhanced emotional memory and HR activity during the anticipatory period in subjects with a past history of PTSD and healthy controls.

METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGMENTS
  8. REFERENCES

Subjects were recruited by advertisements in newspapers and regional flyers and consisted of six women (mean age, 48.7 ± 7.9 years; range, 35–59 years) with a past history of PTSD (past PTSD) as determined by the Structured Clinical Interview for DSM-IV and 12 healthy women (control mean age, 50.7 ± 6.0 years; range, 38–58 years) matched for age, education, and residency. The types of trauma were as follows: diagnosis of cancer in the partner in two; partner's suddendeath in one; and disaster, child abuse, violence by her intimate partner in one each. They were currently free from major medical illnesses and psychopathology. There was no significant difference in the postmenopausal state between past PTSD and control subjects.

On the first test day the subjects viewed an emotionally arousing short story5,6 on a 14-in (35-cm) color monitor while seated comfortably. Prior to slide viewing, each subject was fitted with electrodes for continuous HR monitoring (Biopac MP150 recording system, Monte System, Tokyo). The stories, consisting of 11 slides, were presented as a brief narrated slide show of approximately 5 min.5 The story was divided into three phases: phase 1 (slides 1–4), phase 2 (slides 5–8), and phase 3 (slides 9–11). Phase 1 depicted a mother taking her son to visit his father at work. In phase 2, the boy is caught in a terrible accident, which critically injures him. In phase 3 the mother was shown leaving the hospital. One week later the subjects received an unexpected memory test, 5–9 multiple-choice questions per slide.7 Memory scores were expressed as a percentage of the maximum of each phase. The Institutional Review Board and Ethics Committee of the National Cancer Center approved this study. All of the subjects gave informed consent, and received monetary compensation (¥4000) for their participation.

The pre-HR value was obtained from HR averaged across the 20 s prior to phase 1. At that time point, a slide gave the following instructions: ‘Please watch the following slides carefully.’ The memory scores and HR (pre-HR, phase 1–3) were assessed with a two-way repeated measures analysis of variance (anova). Any relationship between HR and memory scores was calculated with the Spearman's correlation coefficient (rs). Significant effects were assumed at α < 0.01 from a two-tailed test. Data were analyzed using SPSS (Windows version 12.0; SPSS, Chicago, IL, USA). One set of the control group HR data was not obtained because of a technical error.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGMENTS
  8. REFERENCES

The mean recall scores (±SD) for each phase for the past PTSD and control groups were, respectively, phase 1: 53.6 ± 9.3, 48.8 ± 6.9; phase 2: 56.0 ± 14.4, 54.9 ±8.7; and phase 3: 54.5 ± 14.0, 45.2 ± 8.5; The mean HR (±SD) for each phase for the past PTSD and control groups were, respectively, pre-HR: 71.5 ± 10.1 b.p.m., 75.8 ± 20.7 b.p.m.; phase 1: 72.1 ± 9.8 b.p.m., 72.4 ±12.7 b.p.m.; phase 2: 69.1 ± 7.7 b.p.m., 69.7 ± 8.6 b.p.m.; and phase 3: 69.6 ± 8.6 b.p.m., 76.5 ± 27.2 b.p.m. The two-way anova for repeated measures revealed no significant main effects and interactions.

The correlation between HR and memory scores was calculated using only the pre-HR because of no significant HR change during the experiment. As shown in Table 1, a significant correlation was seen between the pre-HR and memory score only on phase 2 in the PTSD group. There was no significant correlation between age and memory scores in either group.

Table 1.  Correlation (rs) between HR and emotional memory score
Memory scorePTSDControlTotal
Phase1Phase2Phase3Phase1Phase2Phase3Phase1Phase2Phase3
  • *

    P < 0.001.

  • HR, heart rate; Pre-HR, heart rate during the anticipatory period; PTSD, post-traumatic stress disorder.

Pre-HR0.710.93*0.84−0.350.21−0.05−0.060.470.34

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGMENTS
  8. REFERENCES

To the best of our knowledge, the present findings are the first to indicate that the association between HR during the anticipatory period and emotional memory strengthens in the subjects with a past history of PTSD. This result supports the speculation of Cahill and Alkire that priming arousal could be associated with memory consolidation.3 Priming arousal, that is, a high pre-HR in the present study, was associated with enhanced emotional memory. Although subjects were not required to infer their own emotions, we can speculate that a heightened pre-HR would be accompanied with an emotional state (e.g. anxiety) during the anticipatory period. It was found only in the past PTSD group, but it is premature to conclude that this relationship was specific in the past PTSD subjects because of the small sample size. Acquired knowledge in this pilot study is that the association may be strengthen in the past PTSD group.

Memory scores in the present study compared with previous studies5,8 were low on phase 2 but comparable on phase 1 and 3. Subjects in the present study were older compared with previous studies (mean age in previous studies: 27.4–34.8 years).5,8 Therefore, the effect of emotional arousal on memory may be differentiated in different age groups.

For HR, there was no significant change during the experiment. The slides used in the present study may not be stressful enough to change the physiological response. Furthermore, HR may not be an appropriate index of the adrenergic system for these slides.

Finally, one possible interpretation could be advanced for the result of a strong relationship between adrenergic activation and emotional memory in the past PTSD group in the present study. There would be some people who had undergone prolonged states of adrenergic activation in the past PTSD group. Orr and Roth suggested that prolonged states of adrenergic activation increased the risk for PTSD through intensified fear conditioning.9

ACKNOWLEDGMENTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGMENTS
  8. REFERENCES

This work was supported in part by a grant from the Japanese Ministry of Health, Labor, and Welfare (Second-Term Comprehensive 10-year strategy for Cancer Control and Research), and by a grant from the Japanese Ministry of Education, Culture, Science, and Technology (Grant-in-Aid for Scientific Research Kakenhi Wakate B-16790711).

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGMENTS
  8. REFERENCES
  • 1
    Ozer EJ, Best SR, Lipsey TL, Weiss DS. Predictors of posttraumatic stress disorder and symptoms in adults: A meta-analysis. Psychol. Bull. 2003; 129: 5273.
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    Pitman RK. Secondary pharmacological prevention of PTSD: Therapeutic implications of a translational model. In: KatoN, KawataM, PitmanRK (eds). PTSD: Brain Mechanisms and Clinical Implications. Springer-Verlag, Tokyo, 2006; 281296.
  • 3
    Cahill L, Alkire MT. Epinephrine enhancement of human memory consolidation: Interaction with arousal at encoding. Neurobiol. Learn. Mem. 2003; 79: 194198.
  • 4
    Nielson KA, Radtke RC, Jensen RA. Arousal-induced modulation of memory storage processes in humans. Neurobiol. Learn. Mem. 1996; 66: 133142.
  • 5
    Cahill L, Prins B, Weber M, McGaugh JL. Beta-adrenergic activation and memory for emotional events. Nature 1994; 371: 702704.
  • 6
    Kazui H, Mori E, Hashimoto M et al. Impact of emotion on memory. Controlled study of the influence of emotionally charged material on declarative memory in Alzheimer's disease. Br. J. Psychiatry 2000; 177: 343347.
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    Cahill L, McGaugh JL. A novel demonstration of enhanced memory associated with emotional arousal. Conscious. Cogn. 1995; 4: 410421.
  • 8
    Cahill L, Babinsky R, Markowitsch HJ, McGaugh JL. The amygdala and emotional memory. Nature 1995; 377: 295296.
  • 9
    Orr SP, Roth WT. Psychophysiological assessment: Clinical applications for PTSD. J. Affect. Disord. 2000; 61: 225240.