Florbela Rocha-Almeida

Huddling, a tactile, thermoregulatory and affiliative social interaction, is a predominant and conserved behaviour for mammalian and bird species. Huddling is particularly important in early life, when thermoregulation, touch and bonding are influential for survival, brain and behavioural development. Our study aims to understand how tactile, vocal and kinship dynamics develop in rat pups. We designed a huddling apparatus where we synchronise huddle formation with ultrasonic vocalisations (USVs). With development, we see that groups (P6–8 vs older pups) stay longer in triad aggregon (pup huddle) configurations in the huddle trial period. Older pups (P18–20) switch huddle states more often; in all ages, join transitions were preferred to breaking. The spectral characteristics of rat pup USVs change in development, with higher peak frequency in P18–20 pups. In all age-groups, we observe vocal quieting as aggregons form. We hypothesised that kinship is a determinant of huddling dynamics but findings reveal otherwise. When comparing kin versus non-kin groups, we found no differences in aggregon durations or switches. In the youngest age (P6–8), USVs were reduced in kin versus non-kin groups, though not in older pups. To address the role of social touch in quieting, we integrated dividers in the huddle arena. Without skin/fur contact, USVs increased in P6–8, P11–14, but not in P18–20 kin groups. We suggest that rat pups have a strong internal drive towards huddling regardless of whether partners are related by kinship. USV analysis suggests that huddling has a calming effect, where related sibling young pups show less USVs overall; absence of social touch is associated with increased vocalisation in young huddle groups. Thus, huddling is a natural social behaviour shared between both related siblings and unrelated conspecifics. Huddling has calming effects–indicated by USVs–that depend on kinship and tactile social contact during the early stages of development.

Huddling, a tactile, thermoregulatory and filial social interaction, is a predominant and conserved social interaction mammalian and bird species. The act of huddling is particularly important in early life, when thermoregulation, social touch and bonding are influential for survival and healthy brain and behavioural development. We ask how tactile, vocal and kinship dynamics of rat pup interactions develop. We designed a huddling apparatus where we record and synchronise huddle formation with ultrasonic vocalisation analysis. With development, we see that groups (P6–8 vs older pups) stay longer in triad aggregon (pup huddle) configurations in the huddle trial period. Older pups (P18–20) switch huddle states more often. The spectral characteristics of rat pup vocalisation during huddling task change in development, with a higher peak frequency in P18–20 pups. In all age-groups we observe vocal quieting as aggregons form. We hypothesized that kinship should be a strong determinant of huddling interactions but our findings reveal otherwise. When comparing kin vs non-kin groups we found no differences in aggregon durations or switches. In the youngest age group (P6–8) the amount of USVs were reduced in kin vs non-kin groups, though not in older age groups. To address the role of tactile contact in quieting we integrated touch dividers in the huddle arena. Without touch, we saw that vocalisations significantly increased in P6–8 and P11 – 14, but not in P18–20 kin sibling groups. We suggest that rat pups have a strong internal drive towards huddling behaviour regardless of whether huddle partners are related by kinship. USV analysis suggests that huddling has a calming effect, where related sibling young pups show less distress overall; absence of touch is associated with increased distress in P6–8 and P11 – 14 kin huddle groups. Thus, huddling is a natural social behaviour that is intrinsically rewarding and shared between both related siblings and unrelated conspecifics; it has calming effects - as indicated by USVs - that depend on kinship and tactile contact during the earliest stages of development.

Social behaviors such as cooperation are crucial for mammals. A deeper knowledge of the neuronal mechanisms underlying cooperation can be beneficial for people suffering from pathologies with impaired social behavior. Our aim was to study the brain activity when two animals synchronize their behavior to obtain a mutual reinforcement. In a previous work, we showed that the activity of the prelimbic cortex (PrL) was enhanced during cooperation in rats, especially in the ones leading most cooperative trials ( leader rats). In this study, we investigated the specific cell type/s in the PrL contributing to cooperative behaviors. To this end, we collected rats’ brains at key moments of the learning process to analyze the levels of c-FOS expression in the main cellular groups of the PrL (glutamatergic cells containing D1 and D2 receptors and interneurons). Leader rats showed increased c-FOS activity in cells expressing D1 receptors during cooperation. In addition, we analyzed the levels of anxiety, dominance, and locomotor behavior, finding that leader rats are in general less anxious and less dominant than followers . We also recorded local field potentials (LFPs) from the PrL, the nucleus accumbens septi (NAc), and the basolateral amygdala (BLA). Spectral analysis showed that delta activity in PrL and NAc increased when rats cooperated, while BLA activity in delta and theta bands decreased considerably during cooperation. The PrL and NAc also increased their connectivity in the high theta band during cooperation. Thus, the present work identifies the specific PrL cell types engaged in this behavior, as well as its connectivity with subcortical brain regions (BLA, NAc) during cooperation. Significance Statement: Brain mechanisms underlying cooperative behaviors remain unknown. The present study identified specific neuronal types from the PrL cortex engaged in the acquisition of a cooperative task, as well as their connectivity with subcortical projection sites, such as the NAc and the BLA during cooperation. Rats leading the cooperation trials (designated leaders ) presented an increased activation of D1-containing neurons in the PrL during cooperation. The PrL and NAc electrical activity increased when rats were cooperating, while the BLA activity increased before cooperation. The PrL and NAc showed increased functional connectivity at the moment of cooperation on the platform, whereas during the individual phase the highest connectivity was found before the animals climbed individually onto the platform.

Brain region coordination in learning: Gamma-frequency oscillations have been hypothesized as a physiological mechanism of interregional communication in the brain. However, until now, all supporting data have been correlational and thus indirect. Fernández-Ruiz et al. examined gamma-frequency activity and spike coupling between the entorhinal cortex and hippocampal dentate gyrus during learning and after selective perturbation of gamma-frequency spike timing. They observed an integrated neuron, gamma-band, and task-specific organization of the entorhinal cortex–hippocampal circuits. These data demonstrate that specific, projected gamma-frequency oscillation patterns dynamically engage functionally related cell assemblies across brain regions in a task-specific manner. Science , this issue p. eabf3119

Longer ripples make better memories: Sharp wave ripples in the hippocampus are thought to play a role in memory formation and action planning. Fernández-Ruiz et al. used multisite electrophysiological recordings combined with optogenetic activation of hippocampal pyramidal neurons in rats performing learning tasks. Learning and correct recall in spatial memory tasks were associated with extended sharp wave ripples. Artificially prolonging these ripples improved working memory performance, whereas aborting the late part of ripples decreased performance. Science , this issue p. 1082