Emotional memory persists longer than event memory

Amygdalo-cortical dialogue underlies memory enhancement by emotional association

Emotional arousal plays a critical role in determining what is remembered from experiences. It is hypothesized that activation of the amygdala by emotional stimuli enhances memory consolidation in its downstream brain regions. However, the physiological basis of the inter-regional interaction and its functions remain unclear. Here, by adding emotional information to a perceptual recognition task that relied on a frontal-sensory cortical circuit in mice, we demonstrated that the amygdala not only associates emotional information with perceptual information but also enhances perceptual memory retention via amygdalo-frontal cortical projections. Furthermore, emotional association increased reactivation of coordinated activity across the amygdalo-cortical circuit during non-rapid eye movement (NREM) sleep but not during rapid eye movement (REM) sleep. Notably, this increased reactivation was associated with amygdala high-frequency oscillations. Silencing of amygdalo-cortical inputs during NREM sleep selectively disrupted perceptual memory enhancement. Our findings indicate that inter-regional reactivation triggered by the amygdala during NREM sleep underlies emotion-induced perceptual memory enhancement.

A dual-systems perspective on temporal cognition: Implications for the role of emotion

This commentary explores how emotion fits in the dual-systems model of temporal cognition proposed by Hoerl & McCormack. The updating system would be affected by emotion via the attentional/arousal effect according to the attentional gate model. The reasoning system would be disrupted by emotion, especially for traumatic events. Time discrepancies described in the dual-systems model are also explained.

Remembering to Forget: A Dual Role for Sleep Oscillations in Memory Consolidation and Forgetting

It has been known since the time of patient H. M. and Karl Lashley's equipotentiality studies that the hippocampus and cortex serve mnestic functions. Current memory models maintain that these two brain structures accomplish unique, but interactive, memory functions. Specifically, most modeling suggests that memories are rapidly acquired during waking experience by the hippocampus, before being later consolidated into the cortex for long-term storage. Sleep has been shown to be critical for the transfer and consolidation of memories in the cortex. Like memory consolidation, a role for sleep in adaptive forgetting has both historical precedent, as Francis Crick suggested in 1983 that sleep was for "reverse-learning," and recent empirical support. In this article I review the evidence indicating that the same brain activity involved in sleep replay associated memory consolidation is responsible for sleep-dependent forgetting. In reviewing the literature, it became clear that both a cellular mechanism for systems consolidation and an agreed upon general, as well as cellular, mechanism for sleep-dependent forgetting is seldom discussed or is lacking. I advocate here for a candidate cellular systems consolidation mechanism wherein changes in calcium kinetics and the activation of consolidative signaling cascades arise from the triple phase locking of non-rapid eye movement sleep (NREMS) slow oscillation, sleep spindle and sharp-wave ripple rhythms. I go on to speculatively consider several sleep stage specific forgetting mechanisms and conclude by discussing a notional function of NREM-rapid eye movement sleep (REMS) cycling. The discussed model argues that the cyclical organization of sleep functions to first lay down and edit and then stabilize and integrate engrams. All things considered, it is increasingly clear that hallmark sleep stage rhythms, including several NREMS oscillations and the REMS hippocampal theta rhythm, serve the dual function of enabling simultaneous memory consolidation and adaptive forgetting. Specifically, the same sleep rhythms that consolidate new memories, in the cortex and hippocampus, simultaneously organize the adaptive forgetting of older memories in these brain regions.

Odor Enrichment Increases Hippocampal Neuron Numbers in Mouse

The hippocampus and olfactory bulb incorporate new neurons migrating from neurogenic regions in the brain. Hippocampal atrophy is evident in numerous neurodegenerative disorders, and altered hippocampal neurogenesis is an early pathological event in Alzheimer's disease. We hypothesized that hippocampal neurogenesis is affected by olfactory stimuli through the neural pathway of olfaction-related memory. In this study, we exposed mice to novel pleasant odors for three weeks and then assessed the number of neurons, non-neuronal cells (mainly glia) and proliferating cells in the hippocampus and olfactory bulb, using the isotropic fractionator method. We found that the odor enrichment significantly increased the neuronal cell numbers in the hippocampus, and promoted cell proliferation and neurogenesis in the olfactory bulb. In contrast, the glial cell numbers remained unchanged in both of the regions. Our results suggest that exposure to novel odor stimuli promotes hippocampal neurogenesis and support the idea that enriched environments may delay the onset or slow down the progression of neurodegenerative disorders.

A specific role for hippocampal mossy fiber's zinc in rapid storage of emotional memories

We investigated the specific role of zinc present in large amounts in the synaptic vesicles of mossy fibers and coreleased with glutamate in the CA3 region. In previous studies, we have shown that blockade of zinc after release has no effect on the consolidation of spatial learning, while zinc is required for the consolidation of contextual fear conditioning. Although both are hippocampo-dependent processes, fear conditioning to the context implies a strong emotional burden. To verify the hypothesis that zinc could play a specific role in enabling sustainable memorization of a single event with a strong emotional component, we used a neuropharmacological approach combining a glutamate receptor antagonist with different zinc chelators. Results show that zinc is mandatory to allow the consolidation of one-shot memory, thus being the key element allowing the hippocampus submitted to a strong emotional charge to switch from the cognitive mode to a flashbulb memory mode. Individual differences in learning abilities have been known for a long time to be totally or partially compensated by distributed learning practice. Here we show that contextual fear conditioning impairments due to zinc blockade can be efficiently reduced by distributed learning practice.

Memory suppression trades prolonged fear and sleep-dependent fear plasticity for the avoidance of current fear

Sleep deprivation immediately following an aversive event reduces fear by preventing memory consolidation during homeostatic sleep. This suggests that acute insomnia might act prophylactically against the development of posttraumatic stress disorder (PTSD) even though it is also a possible risk factor for PTSD. We examined total sleep deprivation and memory suppression to evaluate the effects of these interventions on subsequent aversive memory formation and fear conditioning. Active suppression of aversive memory impaired retention of event memory. However, although the remembered fear was more reduced in sleep-deprived than sleep-control subjects, suppressed fear increased, and seemed to abandon the sleep-dependent plasticity of fear. Active memory suppression, which provides a psychological model for Freud's ego defense mechanism, enhances fear and casts doubt on the potential of acute insomnia as a prophylactic measure against PTSD. Our findings bring into question the role of sleep in aversive-memory consolidation in clinical PTSD pathophysiology.

A quality improvement study on avoidable stressors and countermeasures affecting surgical motor performance and learning

OBJECTIVE

To explore how the 2 most important components of surgical performance--speed and accuracy-are influenced by different forms of stress and what the impact of music is on these factors.

BACKGROUND

On the basis of a recently published pilot study on surgical experts, we designed an experiment examining the effects of auditory stress, mental stress, and music on surgical performance and learning and then correlated the data psychometric measures to the role of music in a novice surgeon's life.

METHODS

Thirty-one surgeons were recruited for a crossover study. Surgeons were randomized to 4 simple standardized tasks to be performed on the SurgicalSIM VR laparoscopic simulator (Medical Education Technologies, Inc, Sarasota, FL), allowing exact tracking of speed and accuracy. Tasks were performed under a variety of conditions, including silence, dichotic music (auditory stress), defined classical music (auditory relaxation), and mental loading (mental arithmetic tasks). Tasks were performed twice to test for memory consolidation and to accommodate for baseline variability. Performance was correlated to the brief Musical Experience Questionnaire (MEQ).

RESULTS

Mental loading influences performance with respect to accuracy, speed, and recall more negatively than does auditory stress. Defined classical music might lead to minimally worse performance initially but leads to significantly improved memory consolidation. Furthermore, psychologic testing of the volunteers suggests that surgeons with greater musical commitment, measured by the MEQ, perform worse under the mental loading condition.

CONCLUSIONS

Mental distraction and auditory stress negatively affect specific components of surgical learning and performance. If used appropriately, classical music may positively affect surgical memory consolidation. It also may be possible to predict surgeons' performance and learning under stress through psychological tests on the role of music in a surgeon's life. Further investigation is necessary to determine the cognitive processes behind these correlations.

Sleep deprivation facilitates extinction of implicit fear generalization and physiological response to fear

BACKGROUND

Neuroendocrine hormones, which regulate both homeostasis and stress responses, provide homeostatic recovery and sleep suppression to brains under stress. We examined the effects of total sleep deprivation on subsequent enhancement of aversive event memory, implicit fear recognition, and fear conditioning in healthy humans.

METHODS

Three different recognitions (explicit event, implicit emotion, and physiological response) were assessed in two groups of 14 healthy young volunteers (sleep control and sleep deprived) with aversive (motor vehicle accident films) and nonaversive episodic memory stimuli. Both groups were tested on Day 1 of the experiment and again on Days 3 and 10; the sleep-deprived group was totally deprived of initial nocturnal sleep after the first trial on Day 1.

RESULTS

Event recognition performances were similar in both groups throughout the study. Implicit fear recognition remained high for aversive stimuli, with generalization of implicit fear recognition occurring for nonaversive stimuli on Day 3 in the sleep control group. Physiological fear and generalized fear responses were observed for every episode, and delayed enhancement of physiological response was only observed for misidentified aversive episodes in the sleep control group on Day 3. However, in the sleep-deprived group, generalization of implicit fear recognition for nonaversive stimuli on Day 3 and all physiological and generalized fear responses on Days 3 and 10 were comprehensively extinguished.

CONCLUSIONS

Clinically, trauma-exposed victims often experience acute insomnia, indicating that such insomnia might provide prophylactic benefits in reducing the development of posttraumatic stress disorder via extinction of the fear-magnifying effects of memory.