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Stuber, G. D., Sparta, D. R., Stamatakis, A. M., van Leeuwen, W. A., Hardjoprajitno, J. E., Cho, S., et al. (2011). Excitatory transmission from the amygdala to nucleus accumbens facilitates reward seeking. Nature, advance online publication.
Abstract: The basolateral amygdala (BLA) has a crucial role in emotional learning irrespective of valence1, 2, 3, 4, 5, 21, 22, 23. The BLA projection to the nucleus accumbens (NAc) is thought to modulate cue-triggered motivated behaviours4, 6, 7, 24, 25, but our understanding of the interaction between these two brain regions has been limited by the inability to manipulate neural-circuit elements of this pathway selectively during behaviour. To circumvent this limitation, we used in vivo optogenetic stimulation or inhibition of glutamatergic fibres from the BLA to the NAc, coupled with intracranial pharmacology and ex vivo electrophysiology. Here we show that optical stimulation of the pathway from the BLA to the NAc in mice reinforces behavioural responding to earn additional optical stimulation of these synaptic inputs. Optical stimulation of these glutamatergic fibres required intra-NAc dopamine D1-type receptor signalling, but not D2-type receptor signalling. Brief optical inhibition of fibres from the BLA to the NAc reduced cue-evoked intake of sucrose, demonstrating an important role of this specific pathway in controlling naturally occurring reward-related behaviour. Moreover, although optical stimulation of glutamatergic fibres from the medial prefrontal cortex to the NAc also elicited reliable excitatory synaptic responses, optical self-stimulation behaviour was not observed by activation of this pathway. These data indicate that whereas the BLA is important for processing both positive and negative affect, the glutamatergic pathway from the BLA to the NAc, in conjunction with dopamine signalling in the NAc, promotes motivated behavioural responding. Thus, optogenetic manipulation of anatomically distinct synaptic inputs to the NAc reveals functionally distinct properties of these inputs in controlling reward-seeking behaviours.
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Wilson, A. M., McGuigan, M. P., Su, A., & van Den Bogert, A. J. (2001). Horses damp the spring in their step. Nature, 414(6866), 895–899.
Abstract: The muscular work of galloping in horses is halved by storing and returning elastic strain energy in spring-like muscle-tendon units.These make the legs act like a child's pogo stick that is tuned to stretch and recoil at 2.5 strides per second. This mechanism is optimized by unique musculoskeletal adaptations: the digital flexor muscles have extremely short fibres and significant passive properties, whereas the tendons are very long and span several joints. Length change occurs by a stretching of the spring-like digital flexor tendons rather than through energetically expensive length changes in the muscle. Despite being apparently redundant for such a mechanism, the muscle fibres in the digital flexors are well developed. Here we show that the mechanical arrangement of the elastic leg permits it to vibrate at a higher frequency of 30-40 Hz that could cause fatigue damage to tendon and bone. Furthermore, we show that the digital flexor muscles have minimal ability to contribute to or regulate significantly the 2.5-Hz cycle of movement, but are ideally arranged to damp these high-frequency oscillations in the limb.
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Moon, C., Baldridge, M. T., Wallace, M. A., Burnham, C. - A. D., Virgin, H. W., & Stappenbeck, T. S. (2015). Vertically transmitted faecal IgA levels determine extra-chromosomal phenotypic variation. Nature, 521(7550), 90–93.
Abstract: The proliferation of genetically modified mouse models has exposed phenotypic variation between investigators and institutions that has been challenging to control1-5. In many cases, the microbiota is the presumed culprit of the variation. Current solutions to account for phenotypic variability include littermate and maternal controls or defined microbial consortia in gnotobiotic mice6,7. In conventionally raised mice, the microbiome is transmitted from the dam2,8,9. Here we show that microbially–driven dichotomous fecal IgA levels in WT mice within the same facility mimic the effects of chromosomal mutations. We observed in multiple facilities that vertically-transmissible bacteria in IgA-Low mice dominantly lowered fecal IgA levels in IgA-High mice after cohousing or fecal transplantation. In response to injury, IgA-Low mice showed increased damage that was transferable by fecal transplantation and driven by fecal IgA differences. We found that bacteria from IgA-Low mice degraded the secretory component (SC) of SIgA as well as IgA itself. These data indicate that phenotypic comparisons between mice must take into account the non-chromosomal hereditary variation between different breeders. We propose fecal IgA as one marker of microbial variability and conclude that cohousing and/or fecal transplantation enables analysis of progeny from different dams.
Keywords: Phenotype
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Clayton, N. S., & Dickinson, A. (1998). Episodic-like memory during cache recovery by scrub jays. Nature, 395(6699), 272–274.
Abstract: The recollection of past experiences allows us to recall what a particular event was, and where and when it occurred1,2, a form of memory that is thought to be unique to humans3. It is known, however, that food-storing birds remember the spatial location4, 5, 6 and contents6, 7, 8, 9 of their caches. Furthermore, food-storing animals adapt their caching and recovery strategies to the perishability of food stores10, 11, 12, 13, which suggests that they are sensitive to temporal factors. Here we show that scrub jays (Aphelocoma coerulescens) remember 'when' food items are stored by allowing them to recover perishable 'wax worms' (wax-moth larvae) and non-perishable peanuts which they had previously cached in visuospatially distinct sites. Jays searched preferentially for fresh wax worms, their favoured food, when allowed to recover them shortly after caching. However, they rapidly learned to avoid searching for worms after a longer interval during which the worms had decayed. The recovery preference of jays demonstrates memory of where and when particular food items were cached, thereby fulfilling the behavioural criteria for episodic-like memory in non-human animals.
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Milinski, M., & Rockenbach, B. (2008). Human behaviour: Punisher pays. Nature, 452(7185), 297–298.
Abstract: The tendency of humans to punish perceived free-loaders, even at a cost to themselves, is an evolutionary puzzle: punishers perish, and those who benefit the most are those who have never punished at all.
Humans are champions of cooperation. Reciprocity – the idea that, if I help you this time, you'll help me next time1 – is a secret of our success. |
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Grosenick, L., Clement, T. S., & Fernald, R. D. (2007). Fish can infer social rank by observation alone. Nature, 445(7126), 429–432.
Abstract: Transitive inference (TI) involves using known relationships to deduce unknown ones (for example, using A > B and B > C to infer A > C), and is thus essential to logical reasoning. First described as a developmental milestone in children, TI has since been reported in nonhuman primates, rats and birds. Still, how animals acquire and represent transitive relationships and why such abilities might have evolved remain open problems. Here we show that male fish (Astatotilapia burtoni) can successfully make inferences on a hierarchy implied by pairwise fights between rival males. These fish learned the implied hierarchy vicariously (as 'bystanders'), by watching fights between rivals arranged around them in separate tank units. Our findings show that fish use TI when trained on socially relevant stimuli, and that they can make such inferences by using indirect information alone. Further, these bystanders seem to have both spatial and featural representations related to rival abilities, which they can use to make correct inferences depending on what kind of information is available to them. Beyond extending TI to fish and experimentally demonstrating indirect TI learning in animals, these results indicate that a universal mechanism underlying TI is unlikely. Rather, animals probably use multiple domain-specific representations adapted to different social and ecological pressures that they encounter during the course of their natural lives.
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Marean, C. W., & Gifford-Gonzalez, D. (1991). Late Quaternary extinct ungulates of East Africa and palaeoenvironmental implications. Nature, 350(6317), 418–420.
Abstract: UNGULATE communities of two East African savannas, the Serengeti and Athi-Kapiti Plains, are dominated by wildebeest (Connochaetes taurinus) supplemented by zebra (Equus burchelli), topi (Damaliscus lunatus), hartebeest (Alcelaphus buselaphus), buffalo (Syncerus caffer) eland (Taurotragus oryx) and gazelles (Gazella grand and G. thomsoni)1-3. Before this research, little was known of East African large mammal communities in the Late Pleistocene and early to middle Holocene. We document an extinct impala-sized alcelaphine antelope that is numerically dominant in Late Pleistocene archaeofaunal assemblages from the Athi-Kapiti Plains. The extinct giant buffalo Pelorovis antiquus is present, and a number of arid-adapted regionally extinct species are common. The small alcelaphine is rare in northern Tanzania, but regionally extinct arid-adapted species are present in Late Pleistocene deposits. These data indicate that as recently as 12,000 years ago, the large mammal community structure of East African savannas was very different and dry grasslands and arid-adapted ungulates expanded at least as far south as northern Tanzania during the Last Glacial Maximum.
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Harrison, S. A., & Tong, F. (2009). Decoding reveals the contents of visual working memory in early visual areas. Nature, 458(7238), 632–635.
Abstract: Visual working memory provides an essential link between perception and higher cognitive functions, allowing for the active maintenance of information about stimuli no longer in view1, 2. Research suggests that sustained activity in higher-order prefrontal, parietal, inferotemporal and lateral occipital areas supports visual maintenance3, 4, 5, 6, 7, 8, 9, 10, 11, and may account for the limited capacity of working memory to hold up to 3–4 items9, 10, 11. Because higher-order areas lack the visual selectivity of early sensory areas, it has remained unclear how observers can remember specific visual features, such as the precise orientation of a grating, with minimal decay in performance over delays of many seconds12. One proposal is that sensory areas serve to maintain fine-tuned feature information13, but early visual areas show little to no sustained activity over prolonged delays14, 15, 16. Here we show that orientations held in working memory can be decoded from activity patterns in the human visual cortex, even when overall levels of activity are low. Using functional magnetic resonance imaging and pattern classification methods, we found that activity patterns in visual areas V1–V4 could predict which of two oriented gratings was held in memory with mean accuracy levels upwards of 80%, even in participants whose activity fell to baseline levels after a prolonged delay. These orientation-selective activity patterns were sustained throughout the delay period, evident in individual visual areas, and similar to the responses evoked by unattended, task-irrelevant gratings. Our results demonstrate that early visual areas can retain specific information about visual features held in working memory, over periods of many seconds when no physical stimulus is present.
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