Hippocampal ripples as a mode of communication with cortical and subcortical areas.

Hippocampal sharp wave-ripple complexes are transient events of highly synchronous neuronal activity that typically occur during "offline" brain states. This endogenous surge of activity consists of behaviorally relevant spiking patterns, describing spatial trajectories. They have been shown to play a critical role in memory consolidation during sleep and in navigational planning during wakefulness. Beyond their local impact on the hippocampal formation, ripples also exert direct and indirect effects on target cortical and subcortical areas, which are thought to play a key role in information processing and semantic network reconfiguration. We review research into the function of hippocampal sharp waves-ripples, with a special focus on information flow between the hippocampus and its cortical and subcortical targets. First, we briefly review seminal work establishing a causal role of ripple-related activity in cognitive processes. We then review evidence for a functional interplay between hippocampal ripples and specific patterns of cortical and subcortical activity. Finally, we discuss the critical role of the functional coupling between ripples and other sleep rhythms, including the cortical slow oscillation and thalamocortical sleep spindles.

A qualitative study of treatment needs among pregnant and postpartum women with substance use and depression.

Little is known about treatment for pregnant and postpartum women with co-occurring substance use and depression. Funded by the National Institute of Drug Abuse, we conducted three focus groups with 18 pregnant and postpartum women in 2011 at an urban substance use treatment clinic. A semi-structured discussion guide probed for factors impacting treatment outcomes and needs. Data were analyzed using grounded theory. Women identified motivational, family, friend, romantic, and agency characteristics as facilitative or challenging to their recoveries, and desired structure (group treatment, a safe environment, and transportation) and content (attention to mental health, family, and gender-specific issues) of treatment.

Associative and predictive hippocampal codes support memory-guided behaviors.

Episodic memory involves learning and recalling associations between items and their spatiotemporal context. Those memories can be further used to generate internal models of the world that enable predictions to be made. The mechanisms that support these associative and predictive aspects of memory are not yet understood. In this study, we used an optogenetic manipulation to perturb the sequential structure, but not global network dynamics, of place cells as rats traversed specific spatial trajectories. This perturbation abolished replay of those trajectories and the development of predictive representations, leading to impaired learning of new optimal trajectories during memory-guided navigation. However, place cell assembly reactivation and reward-context associative learning were unaffected. Our results show a mechanistic dissociation between two complementary hippocampal codes: an associative code (through coactivity) and a predictive code (through sequences).

Locus coeruleus noradrenergic neurons phase-lock to prefrontal and hippocampal infra-slow rhythms that synchronize to behavioral events.

The locus coeruleus (LC) is the primary source of noradrenergic projections to the forebrain, and, in prefrontal cortex, is implicated in decision-making and executive function. LC neurons phase-lock to cortical infra-slow wave oscillations during sleep. Such infra-slow rhythms are rarely reported in awake states, despite their interest, since they correspond to the time scale of behavior. Thus, we investigated LC neuronal synchrony with infra-slow rhythms in awake rats performing an attentional set-shifting task. Local field potential (LFP) oscillation cycles in prefrontal cortex and hippocampus on the order of 0.4 Hz phase-locked to task events at crucial maze locations. Indeed, successive cycles of the infra-slow rhythms showed different wavelengths, as if they are periodic oscillations that can reset phase relative to salient events. Simultaneously recorded infra-slow rhythms in prefrontal cortex and hippocampus could show different cycle durations as well, suggesting independent control. Most LC neurons (including optogenetically identified noradrenergic neurons) recorded here were phase-locked to these infra-slow rhythms, as were hippocampal and prefrontal units recorded on the LFP probes. The infra-slow oscillations also phase-modulated gamma amplitude, linking these rhythms at the time scale of behavior to those coordinating neuronal synchrony. This would provide a potential mechanism where noradrenaline, released by LC neurons in concert with the infra-slow rhythm, would facilitate synchronization or reset of these brain networks, underlying behavioral adaptation.

Rhythmic oscillations in the midbrain dopaminergic nuclei in mice.

Introduction: Dopamine release in the forebrain by midbrain ventral tegmental nucleus (VTA) and substantia nigra pars compacta (SNc) neurons is implicated in reward processing, goal-directed learning, and decision-making. Rhythmic oscillations of neural excitability underlie coordination of network processing, and have been reported in these dopaminergic nuclei at several frequency bands. This paper provides a comparative characterization of several frequencies of oscillations of local field potential and single unit activity, highlighting some behavioral correlates. Methods: We recorded from optogenetically identified dopaminergic sites in four mice training in operant olfactory and visual discrimination tasks. Results: Rayleigh and Pairwise Phase Consistency (PPC) analyses revealed some VTA/SNc neurons phase-locked to each frequency range, with fast spiking interneurons (FSIs) prevalent at 1-2.5 Hz (slow) and 4 Hz bands, and dopaminergic neurons predominant in the theta band. More FSIs than dopaminergic neurons were phase-locked in the slow and 4 Hz bands during many task events. The highest incidence of phase-locking in neurons was in the slow and 4 Hz bands, and occurred during the delay between the operant choice and trial outcome (reward or punishment) signals. Discussion: These data provide a basis for further examination of rhythmic coordination of activity of dopaminergic nuclei with other brain structures, and its impact for adaptive behavior.

Discriminating Sleep From Freezing With Cortical Spindle Oscillations.

In-vivo longitudinal recordings require reliable means to automatically discriminate between distinct behavioral states, in particular between awake and sleep epochs. The typical approach is to use some measure of motor activity together with extracellular electrophysiological signals, namely the relative contribution of theta and delta frequency bands to the Local Field Potential (LFP). However, these bands can partially overlap with oscillations characterizing other behaviors such as the 4 Hz accompanying rodent freezing. Here, we first demonstrate how standard methods fail to discriminate between sleep and freezing in protocols where both behaviors are observed. Then, as an alternative, we propose to use the smoothed cortical spindle power to detect sleep epochs. Finally, we show the effectiveness of this method in discriminating between sleep and freezing in our recordings.

Distributed cell assemblies spanning prefrontal cortex and striatum.

Highly synchronous neuronal assembly activity is deemed essential for cognitive brain function. In theory, such synchrony could coordinate multiple brain areas performing complementary processes. However, cell assemblies have been observed only in single structures, typically cortical areas, and little is known about their synchrony with downstream subcortical structures, such as the striatum. Here, we demonstrate distributed cell assemblies activated at high synchrony (∼10 ms) spanning prefrontal cortex and striatum. In addition to including neurons at different brain hierarchical levels, surprisingly, they synchronized functionally distinct limbic and associative sub-regions. These assembly activations occurred when members shifted their firing phase relative to ongoing 4 Hz and theta rhythms, in association with high gamma oscillations. This suggests that these rhythms could mediate the emergence of cross-structural assemblies. To test for the role of assemblies in behavior, we trained the rats to perform a task requiring cognitive flexibility, alternating between two different rules in a T-maze. Overall, assembly activations were correlated with task-relevant parameters, including impending choice, reward, rule, or rule order. Moreover, these behavioral correlates were more robustly expressed by assemblies than by their individual member neurons. Finally, to verify whether assemblies can be endogenously generated, we found that they were indeed spontaneously reactivated during sleep and quiet immobility. Thus, cell assemblies are a more general coding mechanism than previously envisioned, linking distributed neocortical and subcortical areas at high synchrony.

Post-trauma behavioral phenotype predicts the degree of vulnerability to fear relapse after extinction in male rats.

Current treatments for trauma-related disorders remain ineffective for many patients.1,2 Fear extinction deficiency is a prominent feature of these diseases,3 and many behavioral treatments rely on extinction training.4,5 However, in many patients, therapy is followed by a relapse of symptoms, and the underpinnings of such interindividual variations in vulnerability to relapse remain unknown.6-8 Here, we modeled interindividual differences in post-therapy fear relapse with an ethologically relevant trauma recovery paradigm. After fear conditioning, male rats underwent fear extinction while foraging in a large enriched arena, permitting the expression of a wide spectrum of behaviors. An automated multidimensional behavioral assessment revealed that post-conditioning fear response profiles clustered into two groups: some animals expressed fear by freezing more, whereas others darted more, as if fleeing from danger. Remarkably, the tendency of an animal to dart or to freeze after CS presentation during the first extinction session was, respectively, associated with stronger or weaker fear renewal. Moreover, genome-wide transcriptional profiling revealed that these groups differentially regulated specific sets of genes, some of which were previously implicated in anxiety and trauma-related disorders. Our results suggest that post-trauma behavioral phenotypes and the associated gene expression landscapes can serve as markers of fear relapse susceptibility and thus may be instrumental for future development of more effective treatments for psychiatric patients.

Improving college students' fact-checking strategies through lateral reading instruction in a general education civics course.

College students lack fact-checking skills, which may lead them to accept information at face value. We report findings from an institution participating in the Digital Polarization Initiative (DPI), a national effort to teach students lateral reading strategies used by expert fact-checkers to verify online information. Lateral reading requires users to leave the information (website) to find out whether someone has already fact-checked the claim, identify the original source, or learn more about the individuals or organizations making the claim. Instructor-matched sections of a general education civics course implemented the DPI curriculum (N = 136 students) or provided business-as-usual civics instruction (N = 94 students). At posttest, students in DPI sections were more likely to use lateral reading to fact-check and correctly evaluate the trustworthiness of information than controls. Aligning with the DPI's emphasis on using Wikipedia to investigate sources, students in DPI sections reported greater use of Wikipedia at posttest than controls, but did not differ significantly in their trust of Wikipedia. In DPI sections, students who failed to read laterally at posttest reported higher trust of Wikipedia at pretest than students who read at least one problem laterally. Responsiveness to the curriculum was also linked to numbers of online assignments attempted, but unrelated to pretest media literacy knowledge, use of lateral reading, or self-reported use of lateral reading. Further research is needed to determine whether improvements in lateral reading are maintained over time and to explore other factors that might distinguish students whose skills improved after instruction from non-responders.

"What I thought was so important isn't really that important": international perspectives on making meaning during the first wave of the COVID-19 pandemic.

BACKGROUND: The global COVID-19 pandemic has had a significant impact on the physical and mental health of people everywhere. The aim of the study is to understand how people living in 15 countries around the globe experience an unexpected crisis which threatens their health and that of loved ones, and how they make meaning of this disruption in their narratives. METHODS: Data were collected through an anonymous online survey during May-September 2020, which was during or just after the first wave of the COVID-19 pandemic, depending on the country. The questionnaire included demographic and three open-ended questions as prompts for stories about experiences during the initial months of the pandemic. The text was analyzed through inductive thematic content analysis and quantified for full sample description, demographic and subsequently international comparisons. RESULTS: The final qualitative dataset included stories from n = 1685 respondents. The sample was 73.6% women and 26.4% men. The mean age of participants was 39.55 years (SD = 14.71). The identified four groups of overarching themes were: The presence and absence of others; Rediscovering oneself; The meaning of daily life; Rethinking societal and environmental values. We discuss the prevalence of each theme for the sample as a whole and differences by demographic groups. The most prevalent theme referred to disruptions in interpersonal contacts, made meaningful by the increased appreciation of the value of relationships, present in (45.6%) of stories. It was more prevalent in the stories of women compared to men (χ² = 24.88, p = .001). CONCLUSIONS: The paper provides a detailed overview of the methodology, the main themes identified inductively in the stories and differences according to select demographic variables. We identify several major ways of making meaning of the pandemic. The pandemic has impacted many aspects of people's lives which give it meaning, no matter where they live.

Isolated cortical computations during delta waves support memory consolidation.

Delta waves have been described as periods of generalized silence across the cortex, and their alternation with periods of endogenous activity results in the slow oscillation of slow-wave sleep. Despite evidence that delta waves are instrumental for memory consolidation, their specific role in reshaping cortical functional circuits remains puzzling. In a rat model, we found that delta waves are not periods of complete silence and that the residual activity is not mere neuronal noise. Instead, cortical cells involved in learning a spatial memory task subsequently formed cell assemblies during delta waves in response to transient reactivation of hippocampal ensembles during ripples. This process occurred selectively during endogenous or induced memory consolidation. Thus, delta waves represent isolated cortical computations tightly related to ongoing information processing underlying memory consolidation.

Nested sequences of hippocampal assemblies during behavior support subsequent sleep replay.

Consolidation of spatial and episodic memories is thought to rely on replay of neuronal activity sequences during sleep. However, the network dynamics underlying the initial storage of memories during wakefulness have never been tested. Although slow, behavioral time scale sequences have been claimed to sustain sequential memory formation, fast ("theta") time scale sequences, nested within slow sequences, could be instrumental. We found that in rats traveling passively on a model train, place cells formed behavioral time scale sequences but theta sequences were degraded, resulting in impaired subsequent sleep replay. In contrast, when the rats actively ran on a treadmill while being transported on the train, place cells generated clear theta sequences and accurate trajectory replay during sleep. Our results support the view that nested sequences underlie the initial formation of memory traces subsequently consolidated during sleep.

Hippocampo-cortical coupling mediates memory consolidation during sleep.

Memory consolidation is thought to involve a hippocampo-cortical dialog during sleep to stabilize labile memory traces for long-term storage. However, direct evidence supporting this hypothesis is lacking. We dynamically manipulated the temporal coordination between the two structures during sleep following training on a spatial memory task specifically designed to trigger encoding, but not memory consolidation. Reinforcing the endogenous coordination between hippocampal sharp wave-ripples, cortical delta waves and spindles by timed electrical stimulation resulted in a reorganization of prefrontal cortical networks, along with subsequent increased prefrontal responsivity to the task and high recall performance on the next day, contrary to control rats, which performed at chance levels. Our results provide, to the best of our knowledge, the first direct evidence for a causal role of a hippocampo-cortical dialog during sleep in memory consolidation, and indicate that the underlying mechanism involves a fine-tuned coordination between sharp wave-ripples, delta waves and spindles.

The Positive Effect of a Group Intervention to Reduce Postpartum Depression on Breastfeeding Outcomes in Low-Income Women.

This study examined, as a secondary analysis, whether a group interpersonal psychotherapy (IPT) intervention focused on preventing postpartum depression by strengthening social support and building interpersonal skills during the transition to motherhood positively affected breastfeeding outcomes among low-income women. The intervention-Reach Out, Stand strong, Essentials for new mothers (ROSE)-taught participants the importance of self-care and assertive help seeking to be better able to sustain breastfeeding practices. Ninety-nine pregnant women were randomized to ROSE plus standard care or to standard care alone. Though women in both conditions had similar breastfeeding initiation rates, women in ROSE had longer breastfeeding duration (median days breastfed: 54 vs. 21). Results suggest ROSE may positively affect breastfeeding.