Differences in predictive factors for post-traumatic stress disorder encompassing partial PTSD and full PTSD: a cross-sectional study among individuals exposed to the November 13, 2015 Paris attacks.

Background: When faced with a surge of physically injured individuals, especially following a traumatic event like an attack, frontline practitioners prioritize early triage. Detecting potential psychological injuries soon after such events remains challenging. Some individuals might develop post-traumatic stress disorder (PTSD) according to DSM-V criteria. Others may exhibit PTSD symptoms without meeting full diagnostic criteria, termed partial or sub-syndromal PTSD, a less-explored area in literature. This study aims to identify predictive factors for both full and partial PTSD. Method: In a cohort of victims of the 2015 Paris attacks, multinomial logistic regressions explored predictive factors for partial or full PTSD status 8 to 18 months post-attacks. Analyses considered pre, peri, and posttraumatic factors chosen from literature review and univariate analysis within each group. Results: Within the cohort, 50 individuals showed no signs of PTSD, 35 experienced partial PTSD, and 30 presented with full PTSD. After logistic regression, risk factors associated with full PTSD included a history of trauma (OR = 1.30, CI [1.02-1.66], p < 0.05), the intensity of peri-traumatic physical reactions (OR = 1.22, CI [1.09-1.36], p < 0.001), the difficulties in suppressing intrusive thoughts (OR = 1.11, CI [1.02-1.21], p < 0.013). Only the intensity of peri-traumatic physical reactions emerged as a risk factor for partial PTSD (OR = 1.13, [CI 1.02-1.24], p < 0.001). Discussion: This study revealed that a history of trauma, the intensity of peri-traumatic physical reactions (e.g., tachycardia, trembling, flushes, numbness.), and the difficulties in suppressing intrusive thoughts constitute risk factors for the development of full PTSD. Moreover, the study identified that only the intensity of peri-traumatic physical reactions emerged as a risk factor for partial PTSD. These findings seem to underscore the significance of peri-traumatic experiences in influencing the development of post-traumatic stress symptoms. Conclusion: This study emphasizes the significance of examining peri-traumatic reactions in PTSD development, suggesting its potential as a straightforward screening tool for post-traumatic stress disorder. It also underscores the influence of prior traumatic experiences, before de novo traumatization, in shaping vulnerability to PTSD and illuminates the crucial role of compromised control of intrusive thoughts that could perpetuate PTSD.

The Index of Intrusion Control (IIC): Capturing individual variability in intentional intrusion control in the laboratory.

Intrusive memories can be downregulated using intentional memory control, as measured via the Think/No-Think paradigm. In this task, participants retrieve or suppress memories in response to an associated reminder cue. After each suppression trial, participants rate whether the association intruded into awareness. Previous research has found that repeatedly exerting intentional control over memory intrusions reduces their frequency. This decrease is often summarised with a linear index, which may miss more complex patterns characterising the temporal dynamics of intrusion control. The goal of this paper is to propose a novel metric of intrusion control that captures those dynamic changes over time as a single index. Results from a mega-analysis of published datasets revealed that the change in intrusion frequencies across time is not purely linear, but also includes non-linear dynamics that seem best captured by a log function of the number of suppression attempts. To capture those linear and non-linear dynamics, we propose the Index of Intrusion Control (IIC), which relies on the integral of intrusion changes across suppression attempts. Simulations revealed that the IIC best captured the linear and non-linear dynamics of intrusion suppression when compared with other linear or non-linear indexes of control, such as the regression slope or Spearman correlation, respectively. Our findings demonstrate how the IIC may therefore act as a more reliable metric to capture individual differences in intrusion control, and examine the role of non-linear dynamics characterizing the conscious access to unwanted memories.

Musical experience prior to traumatic exposure as a resilience factor: a conceptual analysis.

Resilience mechanisms can be dynamically triggered throughout the lifecourse by resilience factors in order to prevent individuals from developing stress-related pathologies such as posttraumatic stress disorder (PTSD). Some interventional studies have suggested that listening to music and musical practice after experiencing a traumatic event decrease the intensity of PTSD, but surprisingly, no study to our knowledge has explored musical experience as a potential resilience factor before the potential occurrence of a traumatic event. In the present conceptual analysis, we sought to summarize what is known about the concept of resilience and how musical experience could trigger two key mechanisms altered in PTSD: emotion regulation and cognitive control. Our hypothesis is that the stimulation of these two mechanisms by musical experience during the pre-traumatic period could help protect against the symptoms of emotional dysregulation and intrusions present in PTSD. We then developed a new framework to guide future research aimed at isolating and investigating the protective role of musical experience regarding the development of PTSD in response to trauma. The clinical application of this type of research could be to develop pre-trauma training that promotes emotional regulation and cognitive control, aimed at populations at risk of developing PTSD such as healthcare workers, police officers, and military staffs.

Peritraumatic physical symptoms and the clinical trajectory of PTSD after a terrorist attack: a network model approach.

Introduction: Following a mass casualty event, such as the Paris terrorist attacks of 13 November 2015, first responders need to identify individuals at risk of PTSD. Physical peritraumatic symptoms involving the autonomic nervous system may be useful in this task.Objective: We sought to determine the trajectory of physical response intensity in individuals exposed to the Paris terrorist attacks using repeated measures, and to examine its associations with PTSD. Using network modelling, we examined whether peritraumatic physical symptom associations differed by PTSD status.Methods: Physical reactions were assessed using the Subjective Physical Reactions Scale at three time points: peritraumatic by retrospective recall, then current at one year (8-18 months) and three years (30-42 months) after the attacks. Interaction networks between peritraumatic physical reactions were compared according to PTSD status.Results: On the one hand, the reported intensity of physical reactions was significantly higher in the PTSD group at all time points. On the other hand, using the dynamic approach, more robust positive interactions between peritraumatic physical reactions were found in the PTSD group one and three years after the attacks. Negative interactions were found in the no-PTSD group at one year. Peritraumatic physical numbness was found to be the most central network symptom in the PTSD group, whereas it was least central in the no-PTSD group.Discussion: Network analysis of the interaction between peritraumatic physical subjective responses, particularly physical numbness, may provide insight into the clinical course of PTSD. Our knowledge of the brain regions involved in dissociation supports the hypothesis that the periaqueductal grey may contribute to the process leading to physical numbing.Conclusions: Our findings highlight the role of peritraumatic somatic symptoms in the course of PTSD. Peritraumatic physical numbness appears to be a key marker of PTSD and its identification may help to improve early triage.

Physical numbness was found to be a central symptom in people developing PTSD in our study examining peritraumatic physical symptoms related to the 2015 Paris terrorist attacks.

Attentional capture mediates the emergence and suppression of intrusive memories.

Intrusive memories hijack consciousness and their control may lead to forgetting. However, the contribution of reflexive attention to qualifying a memory signal as interfering is unknown. We used machine learning to decode the brain's electrical activity and pinpoint the otherwise hidden emergence of intrusive memories reported during a memory suppression task. Importantly, the algorithm was trained on an independent attentional model of visual activity, mimicking either the abrupt and interfering appearance of visual scenes into conscious awareness or their deliberate exploration. Intrusion of memories into conscious awareness were decoded above chance. The decoding accuracy increased when the algorithm was trained using a model of reflexive attention. Conscious detection of intrusive activity decoded from the brain signal was central to the future silencing of suppressed memories and later forgetting. Unwanted memories require the reflexive orienting of attention and access to consciousness to be suppressed effectively by inhibitory control.

Altered predictive control during memory suppression in PTSD.

Aberrant predictions of future threat lead to maladaptive avoidance in individuals with post-traumatic stress disorder (PTSD). How this disruption in prediction influences the control of memory states orchestrated by the dorsolateral prefrontal cortex is unknown. We combined computational modeling and brain connectivity analyses to reveal how individuals exposed and nonexposed to the 2015 Paris terrorist attacks formed and controlled beliefs about future intrusive re-experiencing implemented in the laboratory during a memory suppression task. Exposed individuals with PTSD used beliefs excessively to control hippocampal activity during the task. When this predictive control failed, the prediction-error associated with unwanted intrusions was poorly downregulated by reactive mechanisms. This imbalance was linked to higher severity of avoidance symptoms, but not to general disturbances such as anxiety or negative affect. Conversely, trauma-exposed participants without PTSD and nonexposed individuals were able to optimally balance predictive and reactive control during the memory suppression task. These findings highlight a potential pathological mechanism occurring in individuals with PTSD rooted in the relationship between the brain's predictive and control mechanisms.

Avoidance behaviour generalizes to eye processing in posttraumatic stress disorder.

Background: Avoidance describes any action designed to prevent an uncomfortable situation or emotion from occurring. Although it is a common reaction to trauma, avoidance becomes problematic when it is the primary coping strategy, and plays a major role in the development and maintenance of posttraumatic stress disorder (PTSD). Avoidance in PTSD may generalize to non-harmful environmental cues that are perceived to be unsafe. Objective: We tested whether avoidance extends to social cues (i.e. emotional gazes) that are unrelated to trauma. Method: A total of 159 participants (103 who had been exposed to the 2015 Paris terrorist attacks and 56 who had not) performed a gaze-cueing task featuring sad, happy and neutral faces. Attention to the eye area was recorded using an eyetracker. Of the exposed participants, 52 had been diagnosed with PTSD (PTSD+) and 51 had not developed PTSD (PTSD-). As a result of the preprocessing stages, 52 PTSD+ (29 women), 50 PTSD- (20 women) and 53 nonexposed (31 women) participants were included in the final analyses. Results: PTSD+ participants looked at sad eyes for significantly less time than PTSD- and nonexposed individuals. This effect was negatively correlated with the intensity of avoidance symptoms. No difference was found for neutral and happy faces. Conclusions: These findings suggest that maladaptive avoidance in PTSD extends to social processing, in terms of eye contact and others' emotions that are unrelated to trauma. New therapeutic directions could include targeting sociocognitive deficits. Our findings open up new and indirect avenues for overcoming maladaptive avoidance behaviours by remediating eye processing.Trial registration: ClinicalTrials.gov identifier: NCT02810197. HIGHLIGHTS: Avoidance is a key symptom of posttraumatic stress disorder (PTSD).Avoidance is often viewed as limited to reminders linked to the trauma.Results show that attention to the eyes of sad faces is also affected by PTSD. This effect is correlated with avoidance symptoms in PTSD.

Antecedentes: La evitación describe cualquier acción diseñada para prevenir una situación o emoción desagradable. Aunque es una reacción común al trauma, la evitación se vuelve problemática cuando es la principal estrategia de afrontamiento, y desempeña un papel importante en el desarrollo y mantenimiento del trastorno de estrés postraumático (TEPT). La evitación en el TEPT puede generalizarse a señales ambientales no dañinas que se perciben como inseguras. Objetivo: Probamos si la evitación se extiende a las señales sociales (es decir, las miradas emocionales) que no están relacionadas con el trauma. Método: Un total de 159 participantes (103 que habían estado expuestos a los atentados terroristas de París del 2015 y 56 que no lo habían estado) realizaron una tarea de captación de miradas con rostros tristes, felices y neutros. La atención a la zona de los ojos se registró mediante un rastreador ocular. De los participantes expuestos, 52 habían sido diagnosticados con TEPT (TEPT+) y 51 no habían desarrollado TEPT (TEPT-). Resultados: Los participantes con TEPT+ miraron los ojos tristes durante un tiempo significativamente menor que los individuos con TEPT- y los no expuestos. Este efecto se correlacionó negativamente con la intensidad de los síntomas de evitación. No se encontraron diferencias para las caras neutras y felices Conclusiones: Estos hallazgos sugieren que la evitación desadaptativa en el TEPT se extiende al procesamiento social, en cuanto al contacto visual y las emociones de los demás que no están relacionadas con el trauma. Las nuevas direcciones terapéuticas podrían incluir centrarse en los déficits sociocognitivos. Nuestros hallazgos abren vías nuevas e indirectas para superar las conductas de evitación desadaptativas mediante la remediación del procesamiento ocular.

Variations in response to trauma and hippocampal subfield changes.

Models of posttraumatic stress disorder (PTSD) suggest that the hippocampus is key to the persistence of traumatic memory. Yet very little is known about the precise changes that take place in this structure, nor their relation with PTSD symptoms. Previous studies have mostly used magnetic resonance imaging (MRI) at low resolutions, making it impossible to identify sensitive anatomical landmarks, or compared groups often unequally matched in terms of traumatic exposure. The present cross-sectional study included 92 individuals who had all been exposed to the terrorist attacks in Paris on November 13, 2015 (53 of whom subsequently developed PTSD) and 56 individuals who had not been exposed. Hippocampal subfield volumes were estimated using cross-validated automatic segmentation of high-resolution MRI images. Results revealed changes in CA1 and CA2-3/dentate gyrus (DG) volumes in individuals with PTSD, but not in resilient (i.e., exposed but without PTSD) individuals, after controlling for potential nuisance variables such as previous traumatic exposure and substance abuse. In line with current models of hippocampal subfield functions, CA1 changes were linked to the uncontrollable re-experiencing of intrusive memories, while CA2-3/DG changes, potentially exacerbated by comorbid depression, fostered the overgeneralization of fear linked to avoidance and hypervigilance behaviors. Additional analyses revealed that CA1 integrity was linked to optimum functioning of the memory control network in resilient individuals. These findings shed new light on potential pathophysiological mechanisms in the hippocampus subtending the development of PTSD and the failure to recover from trauma.

Long-term modulation of cardiac activity induced by inhibitory control over emotional memories.

Efforts to exclude past experiences from conscious awareness can lead to forgetting. Memory suppression is central to affective disorders, but we still do not really know whether emotions, including their physiological causes, are also impacted by this process in normal functioning individuals. In two studies, we measured the after-effects of suppressing negative memories on cardiac response in healthy participants. Results of Study 1 revealed that efficient control of memories was associated with long-term inhibition of the cardiac deceleration that is normally induced by disgusting stimuli. Attempts to suppress sad memories, by contrast, aggravated the cardiac response, an effect that was closely related to the inability to forget this specific material. In Study 2, electroencephalography revealed a reduction in power in the theta (3-8 Hz), alpha (8-12 Hz) and low-beta (13-20 Hz) bands during the suppression of unwanted memories, compared with their voluntary recall. Interestingly, however, the reduction of power in the theta frequency band during memory control was related to a subsequent inhibition of the cardiac response. These results provide a neurophysiological basis for the influence of memory control mechanisms on the cardiac system, opening up new avenues and questions for treating intrusive memories using motivated forgetting.

Resilience after trauma: The role of memory suppression.

In the aftermath of trauma, little is known about why the unwanted and unbidden recollection of traumatic memories persists in some individuals but not others. We implemented neutral and inoffensive intrusive memories in the laboratory in a group of 102 individuals exposed to the 2015 Paris terrorist attacks and 73 nonexposed individuals, who were not in Paris during the attacks. While reexperiencing these intrusive memories, nonexposed individuals and exposed individuals without posttraumatic stress disorder (PTSD) could adaptively suppress memory activity, but exposed individuals with PTSD could not. These findings suggest that the capacity to suppress memory is central to positive posttraumatic adaptation. A generalized disruption of the memory control system could explain the maladaptive and unsuccessful suppression attempts often seen in PTSD, and this disruption should be targeted by specific treatments.

Collective memory shapes the organization of individual memories in the medial prefrontal cortex.

It has long been hypothesized that individual recollection fits collective memory. To look for a collective schema, we analysed the content of 30 years of media coverage of World War II on French national television. We recorded human brain activity using functional magnetic resonance imaging as participants recalled World War II displays at the Caen Memorial Museum following an initial tour. We focused on the medial prefrontal cortex, a key region for social cognition and memory schemas. The organization of individual memories captured using the distribution of the functional magnetic resonance imaging signal in the dorsal part of the medial prefrontal cortex was more accurately predicted by the structure of the collective schema than by various control models of contextual or semantic memory. Collective memory, which exists outside and beyond individuals, can also organize individual memories and constitutes a common mental model that connects people's memories across time and space.

Influence of emotional complexity on the neural substrates of affective theory of mind.

Affective theory of mind (ToM) depends on both the decoding of emotional expressions and the reasoning on emotional mental states from social situations. While previous studies characterized the neural substrates underlying these processes, it remains unclear whether the nature of the emotional state inferred from others can influence the brain activation associated with affective ToM. In the present study, we focused on two types of emotions: basic emotions (BEs) (e.g., anger and surprise), which are innate and universal and self-conscious emotions (e.g., pride and embarrassment), which correspond to a special class of emotions involving the self and including a representation of one's relative reactions to internal and external standards. Specifically, we used an ecological functional MRI paradigm, on 21 healthy young subjects, to compare brain activations during the decoding of and the reasoning on others' self-conscious, basic and neutral mental states. Our results showed that compared to neutral states, the inference of self-conscious and basic emotional states from others elicited more activation in several core regions of affective ToM. Direct comparisons between emotional conditions revealed more activation for self-conscious than BEs in the right temporoparietal junction during the reasoning process and in left middle occipital regions during the decoding process. Further analyses using a localizer task showed that the extrastriate body area was more recruited for decoding others' self-conscious versus BEs, which emphasize the importance of body clues to properly infer these emotions. Using an original task allowing for an ecological assessment of the affective ToM, these results demonstrate that the complexity of the emotion inferred to others can influence the recruitment of ToM network. This study also validates the use of our task as an ecological tool to assess the affective ToM, constituting an avenue for the characterization of ToM impairments in neurological conditions.

Musical Expertise Increases Top-Down Modulation Over Hippocampal Activation during Familiarity Decisions.

The hippocampus has classically been associated with episodic memory, but is sometimes also recruited during semantic memory tasks, especially for the skilled exploration of familiar information. Cognitive control mechanisms guiding semantic memory search may benefit from the set of cognitive processes at stake during musical training. Here, we examined using functional magnetic resonance imaging, whether musical expertise would promote the top-down control of the left inferior frontal gyrus (LIFG) over the generation of hippocampally based goal-directed thoughts mediating the familiarity judgment of proverbs and musical items. Analyses of behavioral data confirmed that musical experts more efficiently access familiar melodies than non-musicians although such increased ability did not transfer to verbal semantic memory. At the brain level, musical expertise specifically enhanced the recruitment of the hippocampus during semantic access to melodies, but not proverbs. Additionally, hippocampal activation contributed to speed of access to familiar melodies, but only in musicians. Critically, causal modeling of neural dynamics between LIFG and the hippocampus further showed that top-down excitatory regulation over the hippocampus during familiarity decision specifically increases with musical expertise - an effect that generalized across melodies and proverbs. At the local level, our data show that musical expertise modulates the online recruitment of hippocampal response to serve semantic memory retrieval of familiar melodies. The reconfiguration of memory network dynamics following musical training could constitute a promising framework to understand its ability to preserve brain functions.

Parallel Regulation of Memory and Emotion Supports the Suppression of Intrusive Memories.

Intrusive memories often take the form of distressing images that emerge into a person's awareness, unbidden. A fundamental goal of clinical neuroscience is to understand the mechanisms allowing people to control these memory intrusions and reduce their emotional impact. Mnemonic control engages a right frontoparietal network that interrupts episodic retrieval by modulating hippocampal activity; less is known, however, about how this mechanism contributes to affect regulation. Here we report evidence in humans (males and females) that stopping episodic retrieval to suppress an unpleasant image triggers parallel inhibition of mnemonic and emotional content. Using fMRI, we found that regulation of both mnemonic and emotional content was driven by a shared frontoparietal inhibitory network and was predicted by a common profile of medial temporal lobe downregulation involving the anterior hippocampus and the amygdala. Critically, effective connectivity analysis confirmed that reduced amygdala activity was not merely an indirect consequence of hippocampal suppression; rather, both the hippocampus and the amygdala were targeted by a top-down inhibitory control signal originating from the dorsolateral prefrontal cortex. This negative coupling was greater when unwanted memories intruded into awareness and needed to be purged. Together, these findings support the broad principle that retrieval suppression is achieved by regulating hippocampal processes in tandem with domain-specific brain regions involved in reinstating specific content, in an activity-dependent fashion.SIGNIFICANCE STATEMENT Upsetting events sometimes trigger intrusive images that cause distress and that may contribute to psychiatric disorders. People often respond to intrusions by suppressing their retrieval, excluding them from awareness. Here we examined whether suppressing aversive images might also alter emotional responses to them, and the mechanisms underlying such changes. We found that the better people were at suppressing intrusions, the more it reduced their emotional responses to suppressed images. These dual effects on memory and emotion originated from a common right prefrontal cortical mechanism that downregulated the hippocampus and amygdala in parallel. Thus, suppressing intrusions affected emotional content. Importantly, participants who did not suppress intrusions well showed increased negative affect, suggesting that suppression deficits render people vulnerable to psychiatric disorders.

Suppressing Unwanted Memories Reduces Their Unintended Influences.

The ability to control unwanted memories is critical for maintaining cognitive function and mental health. Prior research has shown that suppressing the retrieval of unwanted memories impairs their retention, as measured using intentional (direct) memory tests. Here, we review emerging evidence revealing that retrieval suppression can also reduce the unintended influence of suppressed traces. In particular, retrieval suppression (a) gradually diminishes the tendency for memories to intrude into awareness and (b) reduces memories' unintended expressions on indirect memory tests. We present a neural account in which, during suppression, retrieval cues elicit hippocampally triggered neocortical activity that briefly reinstates features of the original event, which, in turn, are suppressed by targeted neocortical and hippocampal inhibition. This reactivation-dependent reinstatement principle could provide a broad mechanism by which suppressing retrieval of intrusive memories limits their indirect influences.

The origins of repetitive thought in rumination: separating cognitive style from deficits in inhibitory control over memory.

BACKGROUND AND OBJECTIVES: Rumination is a major contributor to the maintenance of affective disorders and has been linked to memory control deficits. However, ruminators often report intentionally engaging in repetitive thought due to its perceived benefits. Deliberate re-processing may lead to the appearance of a memory control deficit that is better explained as a difference in cognitive style. METHODS: Ninety-six undergraduate students volunteered to take part in a direct-suppression variant of the Think/No-Think paradigm after which they completed self-report measures of rumination and the degree to which they deliberately re-processed the to-be-suppressed items. RESULTS: We demonstrate a relation between rumination and impaired suppression-induced forgetting. This relation is robust even when controlling for deliberate re-processing of the to-be-suppressed items, a behavior itself related to both rumination and suppression. Therefore, whereas conscious fixation on to-be-suppressed items reduced memory suppression, it did not fully account for the relation between rumination and memory suppression. LIMITATIONS: The current experiment employed a retrospective measure of deliberate re-processing in the context of an unscreened university sample; future research might therefore generalize our findings using an online measure of deliberate re-processing or within a clinical population. CONCLUSIONS: We provide evidence that deliberate re-processing accounts for some--but not all--of the relation between rumination and suppression-induced forgetting. The present findings, observed in a paradigm known to engage top-down inhibitory modulation of mnemonic processing, provide the most theoretically focused evidence to date for the existence of a memory control deficit in rumination.

[Neuroscience and collective memory: memory schemas linking brain, societies and cultures]. / Neurosciences et mémoires collectives : les schémas entre cerveau, sociétés et cultures.

During the last two decades, the effect of intersubjective relationships on cognition has been an emerging topic in cognitive neurosciences leading through a so-called "social turn" to the formation of new domains integrating society and cultures to this research area. Such inquiry has been recently extended to collective memory studies. Collective memory refers to shared representations that are constitutive of the identity of a group and distributed among all its members connected by a common history. After briefly describing those evolutions in the study of human brain and behaviors, we review recent researches that have brought together cognitive psychology, neuroscience and social sciences into collective memory studies. Using the reemerging concept of memory schema, we propose a theoretical framework allowing to account for collective memories formation with a specific focus on the encoding process of historical events. We suggest that (1) if the concept of schema has been mainly used to describe rather passive framework of knowledge, such structure may also be implied in more active fashions in the understanding of significant collective events. And, (2) if some schema researches have restricted themselves to the individual level of inquiry, we describe a strong coherence between memory and cultural frameworks. Integrating the neural basis and properties of memory schema to collective memory studies may pave the way toward a better understanding of the reciprocal interaction between individual memories and cultural resources such as media or education.

Suppressing unwanted memories reduces their unconscious influence via targeted cortical inhibition.

Suppressing retrieval of unwanted memories reduces their later conscious recall. It is widely believed, however, that suppressed memories can continue to exert strong unconscious effects that may compromise mental health. Here we show that excluding memories from awareness not only modulates medial temporal lobe regions involved in explicit retention, but also neocortical areas underlying unconscious expressions of memory. Using repetition priming in visual perception as a model task, we found that excluding memories of visual objects from consciousness reduced their later indirect influence on perception, literally making the content of suppressed memories harder for participants to see. Critically, effective connectivity and pattern similarity analysis revealed that suppression mechanisms mediated by the right middle frontal gyrus reduced activity in neocortical areas involved in perceiving objects and targeted the neural populations most activated by reminders. The degree of inhibitory modulation of the visual cortex while people were suppressing visual memories predicted, in a later perception test, the disruption in the neural markers of sensory memory. These findings suggest a neurobiological model of how motivated forgetting affects the unconscious expression of memory that may be generalized to other types of memory content. More generally, they suggest that the century-old assumption that suppression leaves unconscious memories intact should be reconsidered.

Temporal predictive codes for spoken words in auditory cortex.

Humans can recognize spoken words with unmatched speed and accuracy. Hearing the initial portion of a word such as "formu…" is sufficient for the brain to identify "formula" from the thousands of other words that partially match. Two alternative computational accounts propose that partially matching words (1) inhibit each other until a single word is selected ("formula" inhibits "formal" by lexical competition) or (2) are used to predict upcoming speech sounds more accurately (segment prediction error is minimal after sequences like "formu…"). To distinguish these theories we taught participants novel words (e.g., "formubo") that sound like existing words ("formula") on two successive days. Computational simulations show that knowing "formubo" increases lexical competition when hearing "formu…", but reduces segment prediction error. Conversely, when the sounds in "formula" and "formubo" diverge, the reverse is observed. The time course of magnetoencephalographic brain responses in the superior temporal gyrus (STG) is uniquely consistent with a segment prediction account. We propose a predictive coding model of spoken word recognition in which STG neurons represent the difference between predicted and heard speech sounds. This prediction error signal explains the efficiency of human word recognition and simulates neural responses in auditory regions.

Is neocortical-hippocampal connectivity a better predictor of subsequent recollection than local increases in hippocampal activity? New insights on the role of priming.

During memory encoding, increased hippocampal activity-thought to reflect the binding of different types of information into unique episodes-has been shown to correlate with subsequent recollection of those episodes. Repetition priming-thought to induce more efficient perceptual processing of stimuli-is normally associated with decreased neocortical activity and is often assumed to reduce encoding into episodic memory. Here, we used fMRI to compare activity to primed and unprimed auditory words in the presence of distracting sounds as a function of whether participants subsequently recollected the word-sound associations or only had a feeling of familiarity with the word in a subsequent surprise recognition task. At the behavioral level, priming increased the incidence of subsequent recollection. At the neuronal level, priming reduced activity in the superior temporal gyrus (STG) but also reversed the traditional increase in encoding-related hippocampal activity associated with subsequent recollection relative to subsequent familiarity. To explain this interaction pattern, further analyses using dynamic causal modeling showed an increase in connectivity from left STG to left hippocampus specific to words that were later recollected. These findings show that successful episodic encoding is not determined solely by local hippocampal activity and emphasize instead the importance of increased functional neocortical-hippocampal coupling. Such coupling might be a better predictor of subsequent recollection than the direction of local hippocampal changes per se. We propose that one consequence of priming is to "free up" attentional resources from processing an item in a noisy context, thereby allowing greater attention to encoding of that context.