Is there anybody out there? Neural circuits of threat detection in vertebrates

Cortical signatures of auditory looming bias show cue-specific adaptation between newborns and young adults

Adaptive biases in favor of approaching, or "looming", sounds have been found across ages and species, thereby implicating the potential of their evolutionary origin and universal basis. The human auditory system is well-developed at birth, yet spatial hearing abilities further develop with age. To disentangle the speculated inborn, evolutionary component of the auditory looming bias from its learned counterpart, we collected high-density electroencephalographic data across human adults and newborns. As distance-motion cues we manipulated either the sound's intensity or spectral shape, which is pinna-induced and thus prenatally inaccessible. Through cortical source localisation we demonstrated the emergence of the bias in both age groups at the level of Heschl's gyrus. Adults exhibited the bias in both attentive and inattentive states; yet differences in amplitude and latency appeared based on attention and cue type. Contrary to the adults, in newborns the bias was elicited only through manipulations of intensity and not spectral cues. We conclude that the looming bias comprises innate components while flexibly incorporating the spatial cues acquired through lifelong exposure.

A non-image-forming visual circuit mediates the innate fear of heights in male mice

The neural basis of fear of heights remains largely unknown. In this study, we investigated the fear response to heights in male mice and observed characteristic aversive behaviors resembling human height vertigo. We identified visual input as a critical factor in mouse reactions to heights, while peripheral vestibular input was found to be nonessential for fear of heights. Unexpectedly, we found that fear of heights in naïve mice does not rely on image-forming visual processing by the primary visual cortex. Instead, a subset of neurons in the ventral lateral geniculate nucleus (vLGN), which connects to the lateral/ventrolateral periaqueductal gray (l/vlPAG), drives the expression of fear associated with heights. Additionally, we observed that a subcortical visual pathway linking the superior colliculus to the lateral posterior thalamic nucleus inhibits the defensive response to height threats. These findings highlight a rapid fear response to height threats through a subcortical visual and defensive pathway from the vLGN to the l/vlPAG.

Evidence for adaptive myelination of subcortical shortcuts for visual motion perception in healthy adults

Conscious visual motion information follows a cortical pathway from the retina to the lateral geniculate nucleus (LGN) and on to the primary visual cortex (V1) before arriving at the middle temporal visual area (MT/V5). Alternative subcortical pathways that bypass V1 are thought to convey unconscious visual information. One flows from the retina to the pulvinar (PUL) and on to medial temporal visual area (MT); while the other directly connects the LGN to MT. Evidence for these pathways comes from non-human primates and modest-sized studies in humans with brain lesions. Thus, the aim of the current study was to reconstruct these pathways in a large sample of neurotypical individuals and to determine the degree to which these pathways are myelinated, suggesting information flow is rapid. We used the publicly available 7T (N = 98; 'discovery') and 3T (N = 381; 'validation') diffusion magnetic resonance imaging datasets from the Human Connectome Project to reconstruct the PUL-MT (including all subcompartments of the PUL) and LGN-MT pathways. We found more fibre tracts with greater density in the left hemisphere. Although the left PUL-MT path was denser, the bilateral LGN-MT tracts were more heavily myelinated, suggesting faster signal transduction. We suggest that this apparent discrepancy may be due to 'adaptive myelination' caused by more frequent use of the LGN-MT pathway that leads to greater myelination and faster overall signal transmission.

Update on neurobiological mechanisms of fear: illuminating the direction of mechanism exploration and treatment development of trauma and fear-related disorders

Fear refers to an adaptive response in the face of danger, and the formed fear memory acts as a warning when the individual faces a dangerous situation again, which is of great significance to the survival of humans and animals. Excessive fear response caused by abnormal fear memory can lead to neuropsychiatric disorders. Fear memory has been studied for a long time, which is of a certain guiding effect on the treatment of fear-related disorders. With continuous technological innovations, the study of fear has gradually shifted from the level of brain regions to deeper neural (micro) circuits between brain regions and even within single brain regions, as well as molecular mechanisms. This article briefly outlines the basic knowledge of fear memory and reviews the neurobiological mechanisms of fear extinction and relapse, which aims to provide new insights for future basic research on fear emotions and new ideas for treating trauma and fear-related disorders.

Subcortico-amygdala pathway processes innate and learned threats

Behavioral flexibility and timely reactions to salient stimuli are essential for survival. The subcortical thalamic-basolateral amygdala (BLA) pathway serves as a shortcut for salient stimuli ensuring rapid processing. Here, we show that BLA neuronal and thalamic axonal activity in mice mirror the defensive behavior evoked by an innate visual threat as well as an auditory learned threat. Importantly, perturbing this pathway compromises defensive responses to both forms of threats, in that animals fail to switch from exploratory to defensive behavior. Despite the shared pathway between the two forms of threat processing, we observed noticeable differences. Blocking β-adrenergic receptors impairs the defensive response to the innate but not the learned threats. This reduced defensive response, surprisingly, is reflected in the suppression of the activity exclusively in the BLA as the thalamic input response remains intact. Our side-by-side examination highlights the similarities and differences between innate and learned threat-processing, thus providing new fundamental insights.

Non-angry aggressive arousal and angriffsberietschaft: A narrative review of the phenomenology and physiology of proactive/offensive aggression motivation and escalation in people and other animals

Human aggression typologies largely correspond with those for other animals. While there may be no non-human equivalent of angry reactive aggression, we propose that human proactive aggression is similar to offense in other animals' dominance contests for territory or social status. Like predation/hunting, but unlike defense, offense and proactive aggression are positively reinforcing, involving dopamine release in accumbens. The drive these motivational states provide must suffice to overcome fear associated with initiating risky fights. We term the neural activity motivating proactive aggression "non-angry aggressive arousal", but use "angriffsberietschaft" for offense motivation in other animals to acknowledge possible differences. Temporal variation in angriffsberietschaft partitions fights into bouts; engendering reduced anti-predator vigilance, redirected aggression and motivational over-ride. Increased aggressive arousal drives threat-to-attack transitions, as in verbal-to-physical escalation and beyond that, into hyper-aggression. Proactive aggression and offense involve related neural activity states. Cingulate, insular and prefrontal cortices energize/modulate aggression through a subcortical core containing subnuclei for each aggression type. These proposals will deepen understanding of aggression across taxa, guiding prevention/intervention for human violence.

Visual spatial location influences selection of instinctive behaviours in mouse

Visual stimuli can elicit instinctive approach and avoidance behaviours. In mouse, vision is known to be important for both avoidance of an overhead threat and approach toward a potential terrestrial prey. The stimuli used to characterize these behaviours, however, vary in both spatial location (overhead or near the ground plane) and visual feature (rapidly expanding disc or slowly moving disc). We therefore asked how mice responded to the same visual features presented in each location. We found that a looming black disc induced escape behaviour when presented overhead or to the side of the animal, but the escapes produced by side-looms were less vigorous and often preceded by freezing behaviour. Similarly, small moving discs induced freezing behaviour when presented overhead or to the side of the animal, but side sweeps also elicited approach behaviours, such that mice explored the area of the arena near where the stimulus had been presented. Our observations therefore show that mice combine cues to the location and features of visual stimuli when selecting among potential behaviours.

Alarm cues and alarmed conspecifics: neural activity during social learning from different cues in Trinidadian guppies

Learning to respond appropriately to novel dangers is often essential to survival and success, but carries risks. Learning about novel threats from others (social learning) can reduce these risks. Many species, including the Trinidadian guppy (Poecilia reticulata), respond defensively to both conspecific chemical alarm cues and conspecific anti-predator behaviours, and in other fish such social information can lead to a learned aversion to novel threats. However, relatively little is known about the neural substrates underlying social learning and the degree to which different forms of learning share similar neural mechanisms. Here, we explored the neural substrates mediating social learning of novel threats from two different conspecific cues (i.e. social cue-based threat learning). We first demonstrated that guppies rapidly learn about threats paired with either alarm cues or with conspecific threat responses (demonstration). Then, focusing on acquisition rather than recall, we discovered that phospho-S6 expression, a marker of neural activity, was elevated in guppies during learning from alarm cues in the putative homologue of the mammalian lateral septum and the preoptic area. Surprisingly, these changes in neural activity were not observed in fish learning from conspecific demonstration. Together, these results implicate forebrain areas in social learning about threat but raise the possibility that circuits contribute to such learning in a stimulus-specific manner.

Social information-mediated population dynamics in non-grouping prey

Abstract

Inadvertent social information (ISI) use, i.e., the exploitation of social cues including the presence and behaviour of others, has been predicted to mediate population-level processes even in the absence of cohesive grouping. However, we know little about how such effects may arise when the prey population lacks social structure beyond the spatiotemporal autocorrelation originating from the random movement of individuals. In this study, we built an individual-based model where predator avoidance behaviour could spread among randomly moving prey through the network of nearby observers. We qualitatively assessed how ISI use may affect prey population size when cue detection was associated with different probabilities and fitness costs, and characterised the structural properties of the emerging detection networks that would provide pathways for information spread in prey. We found that ISI use was among the most influential model parameters affecting prey abundance and increased equilibrium population sizes in most examined scenarios. Moreover, it could substantially contribute to population survival under high predation pressure, but this effect strongly depended on the level of predator detection ability. When prey exploited social cues in the presence of high predation risk, the observed detection networks consisted of a large number of connected components with small sizes and small ego networks; this resulted in efficient information spread among connected individuals in the detection networks. Our study provides hypothetical mechanisms about how temporary local densities may allow information diffusion about predation threats among conspecifics and facilitate population stability and persistence in non-grouping animals.

Significance statement

The exploitation of inadvertently produced social cues may not only modify individual behaviour but also fundamentally influence population dynamics and species interactions. Using an individual-based model, we investigated how the detection and spread of adaptive antipredator behaviour may cascade to changes in the demographic performance of randomly moving (i.e., non-grouping) prey. We found that social information use contributed to population stability and persistence by reducing predation-related per capita mortality and raising equilibrium population sizes when predator detection ability reached a sufficient level. We also showed that temporary detection networks had structural properties that allowed efficient information spread among prey under high predation pressure. Our work represents a general modelling approach that could be adapted to specific predator-prey systems and scrutinise how temporary local densities allow dynamic information diffusion about predation threats and facilitate population stability in non-grouping animals.

Formation of the Looming-evoked Innate Defensive Response during Postnatal Development in Mice

Environmental threats often trigger innate defensive responses in mammals. However, the gradual development of functional properties of these responses during the postnatal development stage remains unclear. Here, we report that looming stimulation in mice evoked flight behavior commencing at P14-16 and had fully developed by P20-24. The visual-evoked innate defensive response was not significantly altered by sensory deprivation at an early postnatal stage. Furthermore, the percentages of wide-field and horizontal cells in the superior colliculus were notably elevated at P20-24. Our findings define a developmental time window for the formation of the visual innate defense response during the early postnatal period and provide important insight into the underlying mechanism.

The subthalamic corticotropin-releasing hormone neurons mediate adaptive REM-sleep responses to threat

When an animal faces a threatening situation while asleep, rapid arousal is the essential prerequisite for an adequate response. Here, we find that predator stimuli induce immediate arousal from REM sleep compared with NREM sleep. Using in vivo neural activity recording and cell-type-specific manipulations, we identify neurons in the medial subthalamic nucleus (mSTN) expressing corticotropin-releasing hormone (CRH) that mediate arousal and defensive responses to acute predator threats received through multiple sensory modalities across REM sleep and wakefulness. We observe involvement of the same neurons in the normal regulation of REM sleep and the adaptive increase in REM sleep induced by sustained predator stress. Projections to the lateral globus pallidus (LGP) are the effector pathway for the threat-coping responses and REM-sleep expression. Together, our findings suggest adaptive REM-sleep responses could be protective against threats and uncover a critical component of the neural circuitry at their basis.

Human threat circuits: Threats of pain, aggressive conspecific, and predator elicit distinct BOLD activations in the amygdala and hypothalamus

INTRODUCTION

Threat processing, enabled by threat circuits, is supported by a remarkably conserved neural architecture across mammals. Threatening stimuli relevant for most species include the threat of being attacked by a predator or an aggressive conspecific and the threat of pain. Extensive studies in rodents have associated the threats of pain, predator attack and aggressive conspecific attack with distinct neural circuits in subregions of the amygdala, the hypothalamus and the periaqueductal gray. Bearing in mind the considerable conservation of both the anatomy of these regions and defensive behaviors across mammalian species, we hypothesized that distinct brain activity corresponding to the threats of pain, predator attack and aggressive conspecific attack would also exist in human subcortical brain regions.

METHODS

Forty healthy female subjects underwent fMRI scanning during aversive classical conditioning. In close analogy to rodent studies, threat stimuli consisted of painful electric shocks, a short video clip of an attacking bear and a short video clip of an attacking man. Threat processing was conceptualized as the expectation of the aversive stimulus during the presentation of the conditioned stimulus.

RESULTS

Our results demonstrate differential brain activations in the left and right amygdala as well as in the left hypothalamus for the threats of pain, predator attack and aggressive conspecific attack, for the first time showing distinct threat-related brain activity within the human subcortical brain. Specifically, the threat of pain showed an increase of activity in the left and right amygdala and the left hypothalamus compared to the threat of conspecific attack (pain > conspecific), and increased activity in the left amygdala compared to the threat of predator attack (pain > predator). Threat of conspecific attack revealed heightened activity in the right amygdala, both in comparison to threat of pain (conspecific > pain) and threat of predator attack (conspecific > predator). Finally, for the condition threat of predator attack we found increased activity in the bilateral amygdala and the hypothalamus when compared to threat of conspecific attack (predator > conspecific). No significant clusters were found for the contrast predator attack > pain.

CONCLUSION

Results suggest that threat type-specific circuits identified in rodents might be conserved in the human brain.

Neurochemically distinct populations of the bed nucleus of stria terminalis modulate innate fear response to weak threat evoked by predator odor stimuli

Anxiety and trauma-related disorders are characterized by significant alterations in threat detection, resulting in inadequate fear responses evoked by weak threats or safety stimuli. Recent research pointed out the important role of the bed nucleus of stria terminalis (BNST) in threat anticipation and fear modulation under ambiguous threats, hence, exaggerated fear may be traced back to altered BNST function. To test this hypothesis, we chemogenetically inhibited specific BNST neuronal populations (corticotropin-releasing hormone - BNST^CRH and somatostatin - BNST^SST expressing neurons) in a predator odor-evoked innate fear paradigm. The rationale for this paradigm was threefold: (1) predatory cues are particularly strong danger signals for all vertebrate species evoking defensive responses on the flight-avoidance-freezing dimension (conservative mechanisms), (2) predator odor can be presented in a scalable manner (from weak to strong), and (3) higher-order processing of olfactory information including predatory odor stimuli is integrated by the BNST. Accordingly, we exposed adult male mice to low and high predatory threats presented by means of cat urine, or low- and high-dose of 2-methyl-2-thiazoline (2MT), a synthetic derivate of a fox anogenital product, which evoked low and high fear response, respectively. Then, we tested the impact of chemogenetic inhibition of BNST^CRH and BNST^SST neurons on innate fear responses using crh- and sst-ires-cre mouse lines. We observed that BNST^SST inhibition was effective only under low threat conditions, resulting in reduced avoidance and increased exploration of the odor source. In contrast, BNST^CRH inhibition had no impact on 2MT-evoked responses, but enhanced fear responses to cat odor, representing an even weaker threat stimulus. These findings support the notion that BNST is recruited by uncertain or remote, potential threats, and CRH and SST neurons orchestrate innate fear responses in complementary ways.

Adult medial habenula neurons require GDNF receptor GFRα1 for synaptic stability and function

The medial habenula (mHb) is an understudied small brain nucleus linking forebrain and midbrain structures controlling anxiety and fear behaviors. The mechanisms that maintain the structural and functional integrity of mHb neurons and their synapses remain unknown. Using spatiotemporally controlled Cre-mediated recombination in adult mice, we found that the glial cell-derived neurotrophic factor receptor alpha 1 (GFRα1) is required in adult mHb neurons for synaptic stability and function. mHb neurons express some of the highest levels of GFRα1 in the mouse brain, and acute ablation of GFRα1 results in loss of septohabenular and habenulointerpeduncular glutamatergic synapses, with the remaining synapses displaying reduced numbers of presynaptic vesicles. Chemo- and optogenetic studies in mice lacking GFRα1 revealed impaired circuit connectivity, reduced AMPA receptor postsynaptic currents, and abnormally low rectification index (R.I.) of AMPARs, suggesting reduced Ca2+ permeability. Further biochemical and proximity ligation assay (PLA) studies defined the presence of GluA1/GluA2 (Ca2+ impermeable) as well as GluA1/GluA4 (Ca2+ permeable) AMPAR complexes in mHb neurons, as well as clear differences in the levels and association of AMPAR subunits with mHb neurons lacking GFRα1. Finally, acute loss of GFRα1 in adult mHb neurons reduced anxiety-like behavior and potentiated context-based fear responses, phenocopying the effects of lesions to septal projections to the mHb. These results uncover an unexpected function for GFRα1 in the maintenance and function of adult glutamatergic synapses and reveal a potential new mechanism for regulating synaptic plasticity in the septohabenulointerpeduncular pathway and attuning of anxiety and fear behaviors.

Behavioral responses of the European mink in the face of different threats: conspecific competitors, predators, and anthropic disturbances

Prey species assess the risk of threat using visual, olfactory, and acoustic cues from their habitat. Thus, they modify their behavior in order to avoid encounters with competitors, predators, and human disturbances that endanger their fitness. European mink (Mustela lutreola) is a critically endangered species that can be preyed upon by larger carnivores and displaced by dominant conspecifics to areas of lower quality, e.g., near to more anthropized localities which may be noisier. In this study, the behavioral responses of 24 European mink were evaluated by conducting an experiment in which the presence of a conspecific competitor was simulated with a visual cue (mirror) and the presence of predators (terrestrial and aerial) with odorous cues. Additionally, they were also exposed to potential sources of anthropic disturbance with acoustic cues (road traffic noise and human voices). Our results showed that European mink were hidden for longer periods of time due to the presence of conspecifics and being exposed to the fecal odors of a terrestrial predator such as dog, but especially when they were exposed to anthropic noises. In the presence of a conspecific, the females and the subadults were the ones who remained hidden for the longest time. As well, they were hidden for longer periods of time due to the presence of conspecifics but in combination with dog feces and anthropic sounds did not induce variations in the response, as both by themselves already triggered an increase in the time they spent hiding. The vigilance model showed the effects of the same factors as the hiding model, but with antagonistic effects in the case of vigilance time which decreased during anthropic noises exposition. Finally, we want to highlight that European mink showed an innate response favorable to all three types of threats, but attention should be focused on human disturbances-as they trigger the most extreme responses-which may affect the rate of survival of this threatened species.

Distinct circuits in rat central amygdala for defensive behaviors evoked by socially signaled imminent versus remote danger

Animals display a rich repertoire of defensive responses adequate to the threat proximity. In social species, these reactions can be additionally influenced by the behavior of fearful conspecifics. However, the majority of neuroscientific studies on socially triggered defensive responses focuses on one type of behavior, freezing. To study a broader range of socially triggered reactions and underlying mechanisms, we directly compared two experimental paradigms, mimicking occurrence of the imminent versus remote threat. Observation of a partner currently experiencing aversive stimulation evokes passive defensive responses in the observer rats. Similar interaction with a partner that has just undergone the aversive stimulation prompts animals to increase active exploration. Although the observers display behaviors similar to those of the aversively stimulated demonstrators, their reactions are not synchronized in time, suggesting that observers' responses are caused by the change in their affective state rather than mimicry. Using opsins targeted to behaviorally activated neurons, we tagged central amygdala (CeA) cells implicated in observers' responses to either imminent or remote threat and reactivated them during the exploration of a novel environment. The manipulation revealed that the two populations of CeA cells promote passive or active defensive responses, respectively. Further experiments confirmed that the two populations of cells at least partially differ in expression of molecular markers (protein kinase C-δ [PKC-δ] and corticotropin-releasing factor [CRF]) and connectivity patterns (receiving input from the basolateral amygdala or from the anterior insula). The results are consistent with the literature on single subjects' fear conditioning, suggesting that similar neuronal circuits control defensive responses in social and non-social contexts.

Nanopolystyrene particles at environmentally relevant concentrations causes behavioral and biochemical changes in juvenile grass carp (Ctenopharyngodon idella)

The biometric, behavioral and biochemical toxicity of polystyrene nanoplastics (PS NPs) in aquatic freshwater vertebrates and in environmentally relevant concentrations remains poorly known. Thus, using different toxicity biomarkers we tested the hypothesis that the exposure of Ctenopharyngodon idella juveniles to small PS NPs concentrations (0.04 ng/L, 34 ng/L and 34 μg/L), for a short period-of-time, may affect their growth/development, individual and collective behavior, and biochemical parameters. Animals exposed to NPs did not show increased biometric parameters (i.e.: body biomass, total and standard length, peduncle height, head height and visceral somatic and hepatosomatic indices). Despite the lack of damage on the locomotor (open field test) and visual (visual stimulus test) abilities of the evaluated fish, the expected increase in locomotor activity during the vibratory stimulus test was not evident in animals exposed to NPs. Non-exposed animals were the only ones showing increased activity/locomotion time in the presence of the predatory stimulus during the individual anti-predatory response test. The behavior of animals directly confronted with a potential predator has evidenced the influence of NPs on shoals' aggregation and on the distance kept by individuals from the predatory stimulus. These changes were associated with PS NPs accumulation in animals' brains, oxidative stress and increased acetylcholinesterase activity (hepatic and cerebral). Therefore, the current study has confirmed the initial hypothesis and showed that, even at low concentrations, PS NPs can affect the health of C. idella individuals at early life stage.

Behavioral and neuronal underpinnings of safety in numbers in fruit flies

Living in a group allows individuals to decrease their defenses, enabling other beneficial behaviors such as foraging. The detection of a threat through social cues is widely reported, however, the safety cues that guide animals to break away from a defensive behavior and resume alternate activities remain elusive. Here we show that fruit flies display a graded decrease in freezing behavior, triggered by an inescapable threat, with increasing group sizes. Furthermore, flies use the cessation of movement of other flies as a cue of threat and its resumption as a cue of safety. Finally, we find that lobula columnar neurons, LC11, mediate the propensity for freezing flies to resume moving in response to the movement of others. By identifying visual motion cues, and the neurons involved in their processing, as the basis of a social safety cue this study brings new insights into the neuronal basis of safety in numbers.

First-Person Virtual Embodiment Modulates the Cortical Network that Encodes the Bodily Self and Its Surrounding Space during the Experience of Domestic Violence

Social aggression, such as domestic violence, has been associated with a reduced ability to take on others’ perspectives. In this naturalistic imaging study, we investigated whether training human participants to take on a first-person embodied perspective during the experience of domestic violence enhances the identification with the victim and elicits brain activity associated with the monitoring of the body and surrounding space and the experience of threat. We combined fMRI measurements with preceding virtual reality exposure from either first-person perspective (1PP) or third-person perspective (3PP) to manipulate whether the domestic abuse stimulus was perceived as directed to oneself or another. We found that 1PP exposure increased body ownership and identification with the virtual victim. Furthermore, when the stimulus was perceived as directed toward oneself, the brain network that encodes the bodily self and its surrounding space was more strongly synchronized across participants and connectivity increased from premotor cortex (PM) and intraparietal sulcus towards superior parietal lobe. Additionally, when the stimulus came near the body, brain activity in the amygdala (AMG) strongly synchronized across participants. Exposure to 3PP reduced synchronization of brain activity in the personal space network, increased modulation of visual areas and strengthened functional connectivity between PM, supramarginal gyrus and primary visual cortex. In conclusion, our results suggest that 1PP embodiment training enhances experience from the viewpoint of the virtual victim, which is accompanied by synchronization in the fronto-parietal network to predict actions toward the body and in the AMG to signal the proximity of the stimulus.

Perineuronal nets and subtypes of GABAergic cells differentiate auditory and multisensory nuclei in the intercollicular area of the midbrain

The intercollicular region, which lies between the inferior and superior colliculi in the midbrain, contains neurons that respond to auditory, visual, and somatosensory stimuli. Golgi studies have been used to parse this region into three distinct nuclei: the intercollicular tegmentum (ICt), the rostral pole of the inferior colliculus (ICrp), and the nucleus of the brachium of the IC (NBIC). Few reports have focused on these nuclei, especially the ICt and the ICrp, possibly due to lack of a marker that distinguishes these areas and is compatible with modern methods. Here, we found that staining for GABAergic cells and perineuronal nets differentiates these intercollicular nuclei in guinea pigs. Further, we found that the proportions of four subtypes of GABAergic cells differentiate intercollicular nuclei from each other and from adjacent inferior collicular subdivisions. Our results support earlier studies that suggest distinct morphology and functions for intercollicular nuclei, and provide staining methods that differentiate intercollicular nuclei and are compatible with most modern techniques. We hope that this will help future studies to further characterize the intercollicular region.

Speedy revelations: how alarm calls can convey rapid, reliable information about urgent danger

In the perpetual struggle between high-speed predators and their prey, individuals need to react in the blink of an eye to avoid capture. Alarm calls that warn of danger therefore need to do so sufficiently rapidly that listeners can escape in time. Paradoxically, many species produce more elements in their alarm calls when signalling about more immediate danger, thereby increasing the reliability of transmission of critical information but taking longer to convey the urgent message. We found that New Holland honeyeaters, Phylidonyris novaehollandiae, incorporated more elements in alarm calls given to more dangerous predators, but video analysis revealed that listeners responded in 100 ms, after only the first element. Consistent with this rapid response, the acoustic structure of the first element varied according to the danger, and playbacks confirmed that birds need hear only the first element to assess risk. However, birds hid for longer and were more likely to flee, after calls with more elements. The dual mechanisms of varying both element structure and number may provide a widespread solution to signalling rapidly and reliably about immediate danger.

Neural dynamics of emotion and cognition: From trajectories to underlying neural geometry

How can we study, characterize, and understand the neural underpinnings of cognitive-emotional behaviors as inherently dynamic processes? In the past 50 years, Stephen Grossberg has developed a research program that embraces the themes of dynamics, decentralized computation, emergence, selection and competition, and autonomy. The present paper discusses how these principles can be heeded by experimental scientists to advance the understanding of the brain basis of behavior. It is suggested that a profitable way forward is to focus on investigating the dynamic multivariate structure of brain data. Accordingly, central research problems involve characterizing "neural trajectories" and the associated geometry of the underlying "neural space." Finally, it is argued that, at a time when the development of neurotechniques has reached a fever pitch, neuroscience needs to redirect its focus and invest comparable energy in the conceptual and theoretical dimensions of its research endeavor. Otherwise we run the risk of being able to measure "every atom" in the brain in a theoretical vacuum.

Chemosensory deficiency may render island-dwelling lizards more vulnerable to invasive predators

Newly introduced predators constitute a major threat to prey populations worldwide. Insular prey animals in particular often do not succeed in overcoming their naivety towards alien predators, making them specifically vulnerable. Why this is the case remains incompletely understood. Here, we investigate how the ability to detect and respond to predator chemical cues varies among populations of the Dalmatian wall lizard, Podarcis melisellensis. Lizards were sampled from five locations in south-eastern Croatia (one mainland location and four islands) that varied in the composition of their predator community. We observed the lizards’ behaviour in response to chemical cues of native saurophagous snakes (the Balkan whip snake, Hierophis gemonensis, and eastern Montpellier snake, Malpolon insignitus) and an introduced mammalian predator (the small Indian mongoose, Herpestes auropunctatus – a species held responsible for the loss of numerous insular reptile populations worldwide). Mainland lizards showed elevated tongue-flick rates (indicative of scent detection) as well as behaviours associated with distress in response to scents of both native and introduced predators. In sharp contrast, island lizards did not alter their behaviour when confronted with any of the predator cues. Alarmingly, even lizards from islands with native predators (both snakes and mammals) and from an island on which mongooses were introduced during the 1920s were non-responsive. This suggests that insular populations are chemosensorily deprived. As failure at the predator-detection level is often seen as the most damaging form of naivety, these results provide further insight into the mechanisms that render insular-living animals vulnerable to invasive species.

Bacterial MgrB peptide activates chemoreceptor Fpr3 in mouse accessory olfactory system and drives avoidance behaviour

Innate immune chemoreceptors of the formyl peptide receptor (Fpr) family are expressed by vomeronasal sensory neurons (VSNs) in the accessory olfactory system. Their biological function and coding mechanisms remain unknown. We show that mouse Fpr3 (Fpr-rs1) recognizes the core peptide motif f-MKKFRW that is predominantly present in the signal sequence of the bacterial protein MgrB, a highly conserved regulator of virulence and antibiotic resistance in Enterobacteriaceae. MgrB peptide can be produced and secreted by bacteria, and is selectively recognized by a subset of VSNs. Exposure to the peptide also stimulates VSNs in freely behaving mice and drives innate avoidance. Our data shows that Fpr3 is required for neuronal detection and avoidance of peptides derived from a conserved master virulence regulator of enteric bacteria.

Neuronal Mechanisms that Drive Organismal Aging Through the Lens of Perception

Sensory neurons provide organisms with data about the world in which they live, for the purpose of successfully exploiting their environment. The consequences of sensory perception are not simply limited to decision-making behaviors; evidence suggests that sensory perception directly influences physiology and aging, a phenomenon that has been observed in animals across taxa. Therefore, understanding the neural mechanisms by which sensory input influences aging may uncover novel therapeutic targets for aging-related physiologies. In this review, we examine different perceptive experiences that have been most clearly linked to aging or age-related disease: food perception, social perception, time perception, and threat perception. For each, the sensory cues, receptors, and/or pathways that influence aging as well as the individual or groups of neurons involved, if known, are discussed. We conclude with general thoughts about the potential impact of this line of research on human health and aging.

Behavioral toxicity of tannery effluent in zebrafish (Danio rerio) used as model system

The ecotoxicity of untreated tannery effluent (UTE) in several animal models has been reported; however, its effects on fish behavior, and neurotoxicity, remain unknown. Thus, the hypothesis that the chronic exposure to UTE can induce behavioral changes in adult zebrafish (Danio rerio) representatives, even when it is highly diluted in water, was tested. Animals exposed to 0.1% and 0.3% UTE for 30 days showed behavioral changes in visual social preference tests through their co-specific and antipredator defensive responses, which had indicated neurotoxic actions. Zebrafish exposed to UTE appeared to have not co-specific preference when it is paired with Poecilia sphrenops. In addition, only animals in the control group showed aversive behavior in the presence of the herein used predatory stimulus (Oreochromis niloticus). However, Cr, Na and Mg bioaccumulation was higher in zebrafish exposed to 0.1% and 0.3% UTE, although anxiogenic and anxiolytic effects were not observed in the models exposed to UTE in the novel tank diving or aggressiveness-increase-in-the-mirror tests. This outcome allowed associating the exposure to the pollutant and bioaccumulation with the observed behavioral changes. The present study is pioneer in scientifically evidencing the sublethal impact caused by chronic exposure to UTE in experimental environment simulating realistic aquatic pollution conditions. Accordingly, results in the current research should motivate further investigations to broaden the knowledge about the real magnitude of UTE biological impacts on the aquatic biota.

Cognitive Control of Escape Behaviour

When faced with potential predators, animals instinctively decide whether there is a threat they should escape from, and also when, how, and where to take evasive action. While escape is often viewed in classical ethology as an action that is released upon presentation of specific stimuli, successful and adaptive escape behaviour relies on integrating information from sensory systems, stored knowledge, and internal states. From a neuroscience perspective, escape is an incredibly rich model that provides opportunities for investigating processes such as perceptual and value-based decision-making, or action selection, in an ethological setting. We review recent research from laboratory and field studies that explore, at the behavioural and mechanistic levels, how elements from multiple information streams are integrated to generate flexible escape behaviour.

Predator odor increases avoidance and glutamatergic synaptic transmission in the prelimbic cortex via corticotropin-releasing factor receptor 1 signaling

Acute exposure to a salient stressor, such as in post-traumatic stress disorder, can have lasting impacts upon an individual and society. To study stress in rodents, some naturalistic methods have included acute exposure to a predator odor, such as the synthetic fox odor 2,4,5, trimethyl-3-thiazoline (TMT). These experiments explore the stress-related behaviors and cortical activity induced by TMT exposure in adult male C57BL/6J mice and the influence of the stress neuropeptide corticotropin-releasing factor (CRF) on these responses. Compared to H2O and a novel odorant, vanilla, mice exposed to TMT in the home cage showed increased avoidance and defensive burying indicative of evident stress responses. Consistent with stress-induced activation of the medial prefrontal cortex (mPFC), we found that the prelimbic (PL) and infralimbic (IL) subregions of the mPFC had elevated c-Fos immunolabeling after TMT and vanilla compared to H2O. Slice physiology recordings were performed in layers 2/3 and 5 of the PL and IL, following TMT, vanilla, or H2O exposure. In TMT mice, but not vanilla or H2O mice, PL layers 2/3 showed heightened spontaneous excitatory post-synaptic currents and synaptic drive, suggesting TMT enhanced excitatory transmission. Synaptic drive in PL was increased in both TMT and H2O mice following bath application of 300 nM CRF, but only H2O mice increased excitatory currents with 100 nM CRF, suggesting dose-effect curve shifts in TMT mice. Further, systemic pretreatment with the CRF-R1 antagonist CP154526 and bath application with the CRF-R1 antagonist NBI27914 reduced excitatory transmission in TMT mice, but not H2O mice. CP154526 also reduced stress-reactive behaviors induced by TMT. Taken together, these findings suggest that exposure to TMT leads to CRF-R1 driven changes in behavior and changes in synaptic function in layer 2/3 neurons in the PL, which are consistent with previous findings that CRF-R1 in the mPFC plays an important role in predator odor-related behaviors.

Sensory Ecology of Predator-Induced Phenotypic Plasticity

Ecological communities are organized in trophic levels that share manifold interactions forming complex food webs. Infochemicals can further modify these interactions, e.g., by inducing defenses in prey. The micro-crustacean Daphnia is able to respond to predator-specific chemical cues indicating an increased predation risk. Daphnia shows plastic responses by adapting its morphology, behavior, and physiology, increasing organism, and population fitness. This stabilizes community structures. This review will describe the progress that has been made in understanding the high degree of plasticity observed in the model crustacean Daphnia. I summarize current knowledge on the processes of predator detection, ranging from the nature of biologically active chemical cues to the underlying neurophysiological mechanisms. With this, I aim to provide a comprehensive overview on the molecular mechanisms of ad hoc environmental phenotypic adaptation. In times of climate change and pollution understanding information transfer in aquatic systems is valuable as it will allow us to predict whether and how community structures are being affected.

Diminishing fear: Optogenetic approach toward understanding neural circuits of fear control

Understanding complex behavioral processes, both learned and innate, requires detailed characterization of the principles governing signal flow in corresponding neural circuits. Previous studies were hampered by the lack of appropriate tools needed to address the complexities of behavior-driving micro- and macrocircuits. The development and implementation of optogenetic methodologies revolutionized the field of behavioral neuroscience, allowing precise spatiotemporal control of specific, genetically defined neuronal populations and their functional connectivity both in vivo and ex vivo, thus providing unprecedented insights into the cellular and network-level mechanisms contributing to behavior. Here, we review recent pioneering advances in behavioral studies with optogenetic tools, focusing on mechanisms of fear-related behavioral processes with an emphasis on approaches which could be used to suppress fear when it is pathologically expressed. We also discuss limitations of these methodologies as well as review new technological developments which could be used in future mechanistic studies of fear behavior.

Speed dependent descending control of freezing behavior in Drosophila melanogaster

The most fundamental choice an animal has to make when it detects a threat is whether to freeze, reducing its chances of being noticed, or to flee to safety. Here we show that Drosophila melanogaster exposed to looming stimuli in a confined arena either freeze or flee. The probability of freezing versus fleeing is modulated by the fly’s walking speed at the time of threat, demonstrating that freeze/flee decisions depend on behavioral state. We describe a pair of descending neurons crucially implicated in freezing. Genetic silencing of DNp09 descending neurons disrupts freezing yet does not prevent fleeing. Optogenetic activation of both DNp09 neurons induces running and freezing in a state-dependent manner. Our findings establish walking speed as a key factor in defensive response choices and reveal a pair of descending neurons as a critical component in the circuitry mediating selection and execution of freezing or fleeing behaviors.

Looming discs are perceived as an innate threat by flies and elicit a survival response. Here, the authors report that flies exhibit either an escape or freezing response depending on their walking speed and identify the involvement of a pair of neurons in mediating the behavior.

Luminance Changes Drive Directional Startle through a Thalamic Pathway

Looming visual stimuli result in escape responses that are conserved from insects to humans. Despite their importance for survival, the circuits mediating visual startle have only recently been explored in vertebrates. Here we show that the zebrafish thalamus is a luminance detector critical to visual escape. Thalamic projection neurons deliver dim-specific information to the optic tectum, and ablations of these projections disrupt normal tectal responses to looms. Without this information, larvae are less likely to escape from dark looming stimuli and lose the ability to escape away from the source of the loom. Remarkably, when paired with an isoluminant loom stimulus to the opposite eye, dimming is sufficient to increase startle probability and to reverse the direction of the escape so that it is toward the loom. We suggest that bilateral comparisons of luminance, relayed from the thalamus to the tectum, facilitate escape responses and are essential for their directionality.

Emotion and the Interactive Brain: Insights From Comparative Neuroanatomy and Complex Systems

Although emotion is closely associated with motivation, and interacts with perception, cognition, and action, many conceptualizations still treat emotion as separate from these domains. Here, a comparative/evolutionary anatomy framework is presented to motivate the idea that long-range, distributed circuits involving the midbrain, thalamus, and forebrain are central to emotional processing. It is proposed that emotion can be understood in terms of large-scale network interactions spanning the neuroaxis that form "functionally integrated systems." At the broadest level, the argument is made that we need to move beyond a Newtonian view of causation to one involving complex systems where bidirectional influences and nonlinearities abound. Therefore, understanding interactions between subsystems and signal integration becomes central to unraveling the organization of the emotional brain.

Divergent midbrain circuits orchestrate escape and freezing responses to looming stimuli in mice

Animals respond to environmental threats, e.g. looming visual stimuli, with innate defensive behaviors such as escape and freezing. The key neural circuits that participate in the generation of such dimorphic defensive behaviors remain unclear. Here we show that the dimorphic behavioral patterns triggered by looming visual stimuli are mediated by parvalbumin-positive (PV⁺) projection neurons in mouse superior colliculus (SC). Two distinct groups of SC PV⁺ neurons form divergent pathways to transmit threat-relevant visual signals to neurons in the parabigeminal nucleus (PBGN) and lateral posterior thalamic nucleus (LPTN). Activations of PV⁺ SC-PBGN and SC-LPTN pathways mimic the dimorphic defensive behaviors. The PBGN and LPTN neurons are co-activated by looming visual stimuli. Bilateral inactivation of either nucleus results in the defensive behavior dominated by the other nucleus. Together, these data suggest that the SC orchestrates dimorphic defensive behaviors through two separate tectofugal pathways that may have interactions.

In response to environmental threats, such as visual looming stimuli, mice either freeze or escape. Here the authors demonstrate that these two behaviors are mediated by separate tectofugal pathways formed by parvalbumin-positive neurons in the superior colliculus.

GABAergic and non-GABAergic projections to the superior colliculus from the auditory brainstem

The superior colliculus (SC) contains an auditory space map that is shaped by projections from several subcortical auditory nuclei. Both GABAergic (inhibitory) and excitatory cells contribute to these inputs, but there are contradictory reports regarding the sources of these inputs. We used retrograde tracing techniques in guinea pigs to identify cells in the auditory brainstem that project to the SC. We combined retrograde tracing with immunohistochemistry for glutamic acid decarboxylase (GAD) to identify putative GABAergic cells that participate in this pathway. Following a tracer injection in the SC, the nucleus of the brachium of the inferior colliculus (NBIC) contained the most labeled cells, followed by the inferior colliculus (IC). Smaller populations were observed in the sagulum, paralemniscal area, periolivary nuclei and ventrolateral tegmental nucleus. Overall, only 10% of the retrogradely labeled cells were GAD immunopositive. The presumptive inhibitory cells were observed in the NBIC, IC, superior paraolivary nucleus, sagulum and paralemniscal area. We conclude that the guinea pig SC receives input from a diverse set of auditory brainstem nuclei, some of which provide GABAergic input. These diverse origins of input to the SC likely represent a variety of functions. Inputs from the NBIC and IC likely provide spatial information for guiding orienting behaviors. Inputs from subcollicular nuclei are less likely to provide spatial information; rather, they may provide a shorter route for auditory information to reach the SC, and could generate avoidance or escape responses to an external threat.

Sex hormones play a role in vulnerability to sleep loss on emotion processing tasks

The central aim of this study was to investigate hormones as a predictor of individual vulnerability or resiliency on emotion processing tasks following one night of sleep restriction. The restriction group was instructed to sleep 3 a.m.–7 a.m. (13 men, 13 women in follicular phase, 10 women in luteal phase of menstrual cycle), and a control group slept 11 p.m.–7 a.m. (12 men, 12 follicular women, 12 luteal women). Sleep from home was verified with actigraphy. Saliva samples were collected on the evening prior to restriction, and in the morning and afternoon following restriction, to measure testosterone, estradiol, and progesterone. In the laboratory, event-related potentials (ERPs) were recorded during presentation of images and faces to index neural processing of emotional stimuli. Compared to controls, sleep-restricted participants had a larger amplitude Late Positive Potential (LPP) ERP to positive vs neutral images, reflecting greater motivated attention towards positive stimuli. Sleep-restricted participants were also less accurate categorizing sad faces and exhibited a larger N170 to sad faces, reflecting greater neural reactivity. Sleep-restricted luteal women were less accurate categorizing all images compared to control luteal women, and progesterone was related to several outcomes. Morning testosterone in men was lower in the sleep-restricted group compared to controls; lower testosterone was associated with lower accuracy to positive images, a greater difference between positive vs neutral LPP amplitude, and lower accuracy to sad and fearful faces. In summary, women higher in progesterone and men lower in testosterone were more vulnerable to the effects of sleep restriction on emotion processing tasks. This study highlights a role for sex and sex hormones in understanding individual differences in vulnerability to sleep loss.

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Sex and sex hormones play a role in individual differences in vulnerability to sleep loss.

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Women higher in progesterone and men lower in testosterone were more vulnerable to the effects of sleep restriction on emotion processing tasks.

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One night of sleep restriction was associated with lower testosterone in men.

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Sleep-restricted participants showed greater motivated attention towards positive picture stimuli compared to rested controls.

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Sleep-restricted participants were less accurate categorizing sad faces and exhibited a larger N170 ERP to sad faces, reflecting greater neural reactivity.

Approaching threatening stimuli cause an expansion of defensive peripersonal space

When sudden environmental stimuli signaling threat occur in the portion of space surrounding the body (defensive peripersonal space), defensive responses are enhanced. Recently Bisio et al. (Bisio A, Garbarini F, Biggio M, Fossataro C, Ruggeri P, Bove M. J Neurosci 37: 2415-2424, 2017) showed that a marker of defensive peripersonal space, the defensive hand-blink reflex, is modulated by the motion of the eliciting threatening stimulus. These results can be parsimoniously explained by the continuous monitoring of environmental threats, resulting in an expansion of defensive peripersonal space when threatening stimuli approach.