Hippocampal activity predicts contextual misattribution of false memories.

Failure of contextual retrieval can lead to false recall, wherein people retrieve an item or experience that occurred in a different context or did not occur at all. Whereas the hippocampus is thought to play a crucial role in memory retrieval, we lack understanding of how the hippocampus supports retrieval of items related to a target context while disregarding related but irrelevant information. Using direct electrical recordings from the human hippocampus, we investigate the neural process underlying contextual misattribution of false memories. In two large datasets, we characterize key physiological differences between correct and false recalls that emerge immediately prior to vocalization. By differentiating between false recalls that share high or low contextual similarity with the target context, we show that low-frequency activity (6 to 18 Hz) in the hippocampus tracks similarity between the current and retrieved context. Applying multivariate decoding methods, we were able to reliably predict the contextual source of the to-be-recalled item. Our findings elucidate one of the hallmark features of episodic memory: our ability to distinguish between memories that were formed on different occasions.

Neural oscillations while remembering traumatic memories in post-traumatic stress disorder.

OBJECTIVE: The current study investigated the oscillatory brain activity of PTSD patients during directed and imaginal exposure to the traumatic memory using magnetoencephalography (MEG), in a paradigm resembling exposure therapy. METHODS: Brain activity of healthy trauma-exposed controls and PTSD participants was measured with MEG as they listened to individualized trauma narratives as well as to a neutral narrative and as they imagined the narrative in detail. Source localization analysis by frequency bands was conducted in order to map neural generators of oscillatory activity. RESULTS: Elicitation of traumatic memories resulted in a distinct neural pattern in PTSD patients compared to healthy trauma-exposed individuals. In response to trauma scripts PTSD patients showed increases in high-gamma band power in visual areas, increased frontal and temporal theta as well as prefrontal alpha and medial temporal beta power relative to neutral scripts. CONCLUSIONS: Results suggest that when recollecting and imagining traumatic memories PTSD patients attempt to engage control or inhibition mechanisms. However, these are either not successfully recruited or inefficient leading to heightened responses and recollection. SIGNIFICANCE: Investigating the oscillatory neural dynamics of PTSD patients can help us better understand the processes underlying trauma re-experiencing.

Neuromodulation of Visual Cortex Reduces the Intensity of Intrusive Memories.

Aversive events can be reexperienced as involuntary and spontaneous mental images of the event. Given that the vividness of retrieved mental images is coupled with elevated visual activation, we tested whether neuromodulation of the visual cortex would reduce the frequency and negative emotional intensity of intrusive memories. Intrusive memories of a viewed trauma film and their accompanied emotional intensity were recorded throughout 5 days. Functional connectivity, measured with resting-state functional magnetic resonance imaging prior to film viewing, was used as predictive marker for intrusions-related negative emotional intensity. Results indicated that an interaction between the visual network and emotion processing areas predicted intrusions' emotional intensity. To test the causal influence of early visual cortex activity on intrusions' emotional intensity, participants' memory of the film was reactivated by brief reminders 1 day following film viewing, followed by inhibitory 1 Hz repetitive transcranial magnetic stimulation (rTMS) over early visual cortex. Results showed that visual cortex inhibitory stimulation reduced the emotional intensity of later intrusions, while leaving intrusion frequency and explicit visual memory intact. Current findings suggest that early visual areas constitute a central node influencing the emotional intensity of intrusive memories for negative events. Potential neuroscience-driven intervention targets designed to downregulate the emotional intensity of intrusive memories are discussed.

Indirect modulation of human visual memory.

Conditions in which memories become maladaptive have inspired extensive research geared to modulate memory by targeting it directly and explicitly. Given limitations of direct memory modulation, we asked the following: can the target memories be modulated indirectly? To address this question, we uniquely targeted visual memories, and leveraged a paradigm utilizing instructions to either forget or remember newly encoded memories. We used a multi-domain approach, and applied the instructions to embedded verbal information presented during encoding (words), with the intention to indirectly modulate recognition of the target visual context memory itself (pictures). Accordingly, participants were presented with two lists of words, where each word was preceded and followed by pictures. Participants were instructed to either remember or forget the first list of words. As expected, the instruction to either remember or forget the words differentially influenced word memory strength. Importantly, the instruction regarding the words, indirectly modulated picture memory strength. Better memory for words resulted in reduced picture memory strength and vice versa, with the instruction to remember the words reducing picture memory strength. Together with a negative correlation between word and picture memory strength, the results suggest a competition for shared resources between memory for content and context. These findings may open new avenues to indirectly modulate maladaptive memories.

Intrusive memories: A mechanistic signature for emotional memory persistence.

Memories of negative emotional events persist more over time relative to memories for neutral information. Such persistence has been attributed to heightened encoding and consolidation processes. However, reactivation of the encoded information may also lead to reduced memory decay through rehearsal or a reconsolidation processes. Here, we tested whether involuntary intrusive memories, spontaneously arising following a stressful event and reactivating its memory, function to prevent memory decay, enhancing its persistence. Participants watched a stressful film containing scenes of aversive material. Memory for the film contents was tested immediately post-film using a visual recognition test. In the following five days, participants recorded intrusive memories of the film using a digitized diary. After 5-days, memory for the film contents was retested. Results indicate that in the immediate aftermath of film watching, participant's memory scores were similarly high for scenes that were later experienced as intrusions and scenes that did not intrude, suggesting effective encoding for all scenes. However, persistence of memory for scenes that intruded was preserved relative to memory for scenes that did not intrude, pointing to a mechanism through which negative intrusive memories persist over time. Implications for memory modification interventions in trauma-related psychopathology are discussed.

Overarching States of Mind.

We all have our varying mental emphases, inclinations, and biases. These individual dispositions are dynamic in that they can change over time and context. We propose that these changing states of mind (SoMs) are holistic in that they exert all-encompassing and coordinated effects simultaneously on our perception, attention, thought, affect, and behavior. Given the breadth of their reach, understanding how SoMs operate is essential. We provide evidence and a framework for the concept of SoM, and we propose a unifying principle for the underlying cortical mechanism whereby SoM is determined by the balance between top-down (TD) and bottom-up (BU) processing. This novel global account gives rise to unique hypotheses and opens new horizons for understanding the human mind.

Brain responses to other people's pain in fibromyalgia: a magnetoencephalography study.

OBJECTIVES: We investigated whether the central pain symptoms in fibromyalgia syndrome (FM) are related to defective top-down sensorimotor regulation. The pain matrix was activated in a top-down manner by presenting pictures of painful situations while recording brain activity using magnetoencephalography (MEG). We investigated alpha desynchronisation in FM patients and healthy controls in response to pictures depicting pain. METHODS: 19 FM patients and 14 age-matched healthy controls (age 20-60) were recruited. Participants were shown photographs of right hands and feet in situations depicting pain or of control situations with no depiction of pain. MEG was recorded in a whole-head 248-sensor system as subjects laid supine. RESULTS: In healthy controls exposure to pictures depicting painful situations elicited a decrease in alpha activity (10Hz) at 100-500ms post-stimulus, which was significantly more pronounced than the one elicited by non-painful content mostly on sensors above the right sensorimotor cortex. However, FM patients did not show significant differences in alpha activity between responses to pain and no-pain pictures. CONCLUSIONS: Consistent with previous findings, healthy participants displayed stronger alpha desynchronisation for pain pictures, indicating automatic disinhibition of the sensorimotor cortices in response to the observation of pain in others. We found evidence for a deficient modulation of sensorimotor cortex in FM patients. The lack of differential response suggests that they perceived relatively neutral pictures as potentially painful, at least in this setting. Our findings suggest that defective top-down regulation may play a role in the pathogenesis of FM.

Neural correlates of attention bias in posttraumatic stress disorder.

OBJECTIVE: Patients suffering from posttraumatic stress disorder (PTSD) exhibit hyper arousal symptoms and attention problems which were frequently investigated using the P3 event-related potentials (ERPs). Our study aimed at providing more precise knowledge of the functional significance of the P3 alteration seen in PTSD by revealing its spatio-temporal dynamics. METHODS: Fifteen PTSD patients and fifteen healthy trauma-exposed controls participated in a three-tone "oddball" task while their brain activity was recorded by magnetoencephalography (MEG). They were asked to detect rare target tones and ignore standard tones and infrequent threatening distractors. An adaptive spatial-filter method (SAM beamformer) was applied for source estimation. RESULTS: Compared with controls, PTSD patients had more incorrect responses to standard stimuli. On the brain level, PTSD patients showed hyperactivity in the dorsolateral prefrontal cortex and anterior cingulate cortex in response to standard sounds, decreased activity in those regions in response to threatening distractors, and decreased orbitofrontal activity in response to target stimuli. CONCLUSIONS: Increased frontal activation in response to standard, neutral, stimuli may reflect greater resource allocation dedicated to cognitive control mechanisms during routine functioning in PTSD. Decreased frontal activation in response to rare stimuli may reflect subsequently reduced residual resources for detecting rare stimuli and for emotion regulation. This may explain the hypervigilance and attention problems commonly reported by patients. SIGNIFICANCE: The current findings contribute to a better understanding of the mechanisms underlying the attention deficiency in PTSD, and highlight altered activity in specific frontal regions as potential biomarkers.