Threat history controls flexible escape behavior in mice

Doppler detection triggers instantaneous escape behavior in scanning bats

Animals must instantaneously escape from predators for survival, which requires quick detection of approaching threats. Although the neural mechanisms underlying the perception of looming objects have been extensively studied in the visual system, little is known about their auditory counterparts. Echolocating bats use their auditory senses to perceive not only the soundscape, but also the physical environment through active sensing. Although object movement induces both echo delay changes and Doppler shifts, the actual information required to perceive movement has been unclear. Herein, we addressed this question by playing back phantom echoes mimicking an approaching target to horseshoe bats and found that they relied only on Doppler shifts. This suggests that the bats do not perceive object motion in the spatiotemporal dimension (i.e., positional variation), as in vision, but rather take advantage of acoustic sensing by directly detecting velocity, thereby enabling them to respond instantaneously to approaching threats.

Prefrontal control of superior colliculus modulates innate escape behavior following adversity

Innate defensive responses, though primarily instinctive, must also be highly adaptive to changes in risk assessment. However, adaptive changes can become maladaptive, following severe stress, as seen in posttraumatic stress disorder (PTSD). In a series of experiments, we observed long-term changes in innate escape behavior of male mice towards a previously non-threatening stimulus following an adverse shock experience manifested as a shift in the threshold of threat response. By recording neural activity in the superior colliculus (SC) while phototagging specific responses to afferents, we established the crucial influence of input arriving at the SC from the medial prefrontal cortex (mPFC), both directly and indirectly, on escape-related activity after adverse shock experience. Inactivating these specific projections during the shock effectively abolished the observed changes. Conversely, optogenetically activating them during encounters controlled escape responses. This establishes the necessity and sufficiency of those specific mPFC inputs into the SC for adverse experience related changes in innate escape behavior.

Automated behavioral analysis reveals that mice employ a bait-and-switch escape mechanism to de-escalate social conflict

Intraspecies aggression has profound ecological and evolutionary consequences, as recipients can suffer injuries, decreases in fitness, and become outcasts from social groups. Although animals implement diverse strategies to avoid hostile confrontations, the extent to which social influences affect escape tactics is unclear. Here, we used computational and machine-learning approaches to analyze complex behavioral interactions as mixed-sex groups of mice, Mus musculus, freely interacted. Mice displayed a rich repertoire of behaviors marked by changes in behavioral state, aggressive encounters, and mixed-sex interactions. A prominent behavioral sequence consistently occurred after aggressive encounters, where males in submissive states quickly approached and transiently interacted with females immediately before the aggressor engaged with the same female. The behavioral sequences were also associated with substantially fewer physical altercations. Furthermore, the male's behavioral state and the interacting partners could be predicted by distinct features of the behavioral sequence, such as kinematics and the latency to and duration of male-female interactions. More broadly, our work revealed an ethologically relevant escape strategy influenced by the presence of females that may serve as a mechanism for de-escalating social conflict and preventing consequential reductions in fitness.

Distinct circuits in anterior cingulate cortex encode safety assessment and mediate flexibility of fear reactions

Safety assessment and threat evaluation are crucial for animals to live and survive in the wilderness. However, neural circuits underlying safety assessment and their transformation to mediate flexibility of fear-induced defensive behaviors remain largely unknown. Here, we report that distinct neuronal populations in mouse anterior cingulate cortex (ACC) encode safety status by selectively responding under different contexts of auditory threats, with one preferably activated when an animal staysing in a self-deemed safe zone and another specifically activated in more dangerous environmental settings that led to escape behavior. The safety-responding neurons preferentially target the zona incerta (ZI), which suppresses the superior colliculus (SC) via its GABAergic projection, while the danger-responding neurons preferentially target and excite SC. These distinct corticofugal pathways antagonistically modulate SC responses to threat, resulting in context-dependent expression of fear reactions. Thus, ACC serves as a critical node to encode safety/danger assessment and mediate behavioral flexibility through differential top-down circuits.

Dual Receptive Fields Underlying Target and Wide-Field Motion Sensitivity in Looming-Sensitive Descending Neurons

Responding rapidly to visual stimuli is fundamental for many animals. For example, predatory birds and insects alike have amazing target detection abilities, with incredibly short neural and behavioral delays, enabling efficient prey capture. Similarly, looming objects need to be rapidly avoided to ensure immediate survival, as these could represent approaching predators. Male Eristalis tenax hoverflies are nonpredatory, highly territorial insects that perform high-speed pursuits of conspecifics and other territorial intruders. During the initial stages of the pursuit, the retinal projection of the target is very small, but this grows to a larger object before physical interaction. Supporting such behaviors, E. tenax and other insects have both target-tuned and loom-sensitive neurons in the optic lobes and the descending pathways. We here show that these visual stimuli are not necessarily encoded in parallel. Indeed, we describe a class of descending neurons that respond to small targets, to looming and to wide-field stimuli. We show that these descending neurons have two distinct receptive fields where the dorsal receptive field is sensitive to the motion of small targets and the ventral receptive field responds to larger objects or wide-field stimuli. Our data suggest that the two receptive fields have different presynaptic input, where the inputs are not linearly summed. This novel and unique arrangement could support different behaviors, including obstacle avoidance, flower landing, and target pursuit or capture.

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.

Activation of Parabrachial Tachykinin 1 Neurons Counteracts Some Behaviors Mediated by Parabrachial Calcitonin Gene-related Peptide Neurons

Many threats activate parabrachial neurons expressing calcitonin gene-related peptide (CGRP^PBN) which transmit alarm signals to forebrain regions. Most CGRP^PBN neurons also express tachykinin 1 (Tac1), but there are also Tac1-expressing neurons in the PBN that do not express CGRP (Tac1+;CGRP- neurons). Chemogenetic or optogenetic activation of all Tac1^PBN neurons in mice elicited many physiological/behavioral responses resembling the activation of CGRP^PBN neurons, e.g., anorexia, jumping on a hot plate, avoidance of photostimulation; however, two key responses opposed activation of CGRP^PBN neurons. Activating Tac1^PBN neurons did not produce conditioned taste aversion and it elicited dynamic escape behaviors rather than freezing. Activating Tac1+;CGRP- neurons, using an intersectional genetic targeting approach, resembles activating all Tac1^PBN neurons. These results reveal that activation of Tac1+;CGRP- neurons can suppress some functions attributed to the CGRP^PBN neurons, which provides a mechanism to bias behavioral responses to threats.

Male and female mice display consistent lifelong ability to address potential life-threatening cues using different post-threat coping strategies

BACKGROUND

Sex differences ranging from physiological functions to pathological disorders are developmentally hard-wired in a broad range of animals, from invertebrates to humans. These differences ensure that animals can display appropriate behaviors under a variety of circumstances, such as aggression, hunting, sleep, mating, and parental care, which are often thought to be important in the acquisition of resources, including territory, food, and mates. Although there are reports of an absence of sexual dimorphism in the context of innate fear, the question of whether there is sexual dimorphism of innate defensive behavior is still an open question. Therefore, an in-depth investigation to determine whether there are sex differences in developmentally hard-wired innate defensive behaviors in life-threatening circumstances is warranted.

RESULTS

We found that innate defensive behavioral responses to potentially life-threatening stimuli between males and females were indistinguishable over their lifespan. However, by using 3 dimensional (3D)-motion learning framework analysis, we found that males and females showed different behavioral patterns after escaping to the refuge. Specifically, the defensive "freezing" occurred primarily in males, whereas females were more likely to return directly to exploration. Moreover, there were also no estrous phase differences in innate defensive behavioral responses after looming stimuli.

CONCLUSIONS

Our results demonstrate that visually-evoked innate fear behavior is highly conserved throughout the lifespan in both males and females, while specific post-threat coping strategies depend on sex. These findings indicate that innate fear behavior is essential to both sexes and as such, there are no evolutionary-driven sex differences in defensive ability.