Stress biases negative associations in the brain
Regions showing stress-potentiated aversive PE signal.
From soldiers in combat to students taking final exams, extreme stress can elicit long-term, debilitating emotional responses in people, but the mechanisms underlying such responses are not well understood. Through a study that combines a translational model of stress with cognitive neuroimaging, Oliver Robinson et al. (pp. 4129–4133) demonstrate that stress heightens an aversive prediction error (PE) signal within a brain region called the ventral striatum via a learning pathway triggered by mismatches between expected and observed outcomes. Using a foot shock protocol adapted from rodent studies, the authors found that stress increases the aversive PE signal within the ventral striatum but has no significant effect when the predicted outcome is unexpectedly positive. The results augment earlier studies that have identified PE processing as a likely driver of stimulus–outcome associations, and show that stress can bias the process toward associations that may allow organisms to adapt and instinctively avoid danger. The findings constitute a potential mechanism by which stressful situations lay down threat-related associations in both healthy and pathologically anxious individuals, and provide direction for future research aimed at treating stress-related disorders, according to the authors. — T.J.
Bats adjust their echolocating calls to compete with sounds of nature
Greater Horseshoe Bat, Rhinolophus ferrumequinum, in roosting position.
Birds, humans, and other animals instinctively raise their voices to communicate over the din of a bustling environment—a phenomenon known as the Lombard effect—but the specific auditory changes that accompany this effect in animals remain unclear. Steffen Hage et al. (pp. 4063–4068) studied the Lombard effect in a highly vocal mammal, the echolocating horseshoe bat, to determine if the increased speech amplitude, frequency, and word duration observed in humans’ Lombard effect mirror the vocal changes of bats. The authors examined the frequency and amplitude of more than 83,000 echolocation calls from three bats in response to playbacks of the bats’ natural, non-Lombard calls broadcast over varying frequencies of filtered noise. The authors tested the effects of background noise on various factors, including the ability to listen to communication calls and to low-frequency ambient noise, like the sound of raindrops falling on vegetation. Call frequency increased in response to nearly all frequencies of background noise, but call amplitude increased only when the background noise was played at the frequency typically associated with echolocation. Bats constantly adjust their echolocation pulses by monitoring the returning echoes of their own voices, the authors note, and the rapid vocal adjustment to the background noise could indicate that the underlying neuronal networks responsible for the Lombard effect might function without direct auditory feedback. The findings suggest a direct connection between the auditory and vocal-motor neural systems, according to the authors. —A.G.
Engineering bone by simulating native bone development
Cross-section of an engineered bone organ.
Researchers have established that stem cells derived from adult human bone marrow can generate mature bone, bone matrix, and marrow-associated hematopoietic tissues by forming a cartilaginous intermediate. To develop a scaled-up “bone organ,” including a functional hematopoietic compartment, where blood cells originate, Celeste Scotti et al. (pp. 3997–4002) grew adult human bone marrow–derived stem cells on collagen-based scaffolds in a nutrient-supplemented medium. The authors implanted the resulting cartilage under the skin of mice, and monitored bone development over 12 weeks. Mice implanted with the cartilage, the authors report, developed a full-fledged “bone organ” with native bone-like size, structure, and properties, including mature vascular networks and large marrow spaces housing functional hematopoietic stem cells. The authors found that the marrow cavities contained well-defined hematopoietic stem cells and their progenitors at frequencies similar to those seen in native bones. Further, the engineered bone was composed of an outer layer largely generated by the mouse cells over a mineralized area, and an inner layer mainly formed by the human cells over the cartilaginous template. Because the process resembles the embryonic development of native bones, the authors suggest that an approach based on developmental engineering might improve efforts to model and restore bone tissues and hematopoiesis. — P.N.
Dynamics of old-growth forests
Old-growth forest ecosystems can be considered a steady-state mosaic of patches in different successional stages, with the fraction of the landscape in any particular stage relatively constant over large temporal and spatial scales. Noting that the size and timing of ecosystem-disturbing events and recovery processes determine the spatial scale of the steady-state, Jeffrey Chambers et al. (pp. 3949–3954) integrated field plot data, remote sensing disturbance probability distribution functions, and model simulations to characterize the mosaic for a Central Amazon forest. According to the authors, a steady state with patches of varying successional ages can occur over large spatial scales, potentially biasing temporal trends detected from plots that sample a relatively small fraction of the landscape. A model-based analysis of the Central Amazon forest, the authors report, revealed that previous analyses scaled to the larger region failed to capture nearly 17% of tree mortality because the plots failed to capture the spatial dynamics of the mosaic. The study demonstrates that ecosystem disturbance and recovery cycles can drive complex, large-scale structure in old-growth tropical forests, underscoring the need to combine plot and remote sensing methods to investigate landscape processes, according to the authors. — T.J.
Male jays might intuit mates’ food preferences
Male Eurasian jay shares food with its female partner.
Psychologists define state-attribution as the ability to infer that others possess an internal life similar to one’s own, with psychological states such as desire, hope, and belief underlying people’s actions. Previous studies have largely failed to implement testing protocols that adequately integrate key factors of state attribution identified by evolutionary and developmental psychology and other important findings related to empathy. Ljerka Ostojić et al. (pp. 4123–4128) devised a behavioral paradigm to address these shortcomings and investigate whether male Eurasian jays respond to the changing desire-state of female partners when sharing food. The authors demonstrate that male jays flexibly cater to their mates’ changing food preferences and, more importantly, need to see which foods females have previously eaten in order to accurately assess their current desires. As such, the authors suggest, the male birds are not merely responding to behavioral cues that indicate the females’ preferences or the males’ own agendas. Instead, the results suggest that Eurasian jays may be able to ascribe desire-states to their mates, according to the authors. — T.J.