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A cortex-like canonical circuit in the avian forebrain

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Basic principles of bird and mammal brains

Mammals can be very smart. They also have a brain with a cortex. It has thus often been assumed that the advanced cognitive skills of mammals are closely related to the evolution of the cerebral cortex. However, birds can also be very smart, and several bird species show amazing cognitive abilities. Although birds lack a cerebral cortex, they do have pallium, and this is considered to be analogous, if not homologous, to the cerebral cortex. An outstanding feature of the mammalian cortex is its layered architecture. In a detailed anatomical study of the bird pallium, Stacho et al. describe a similarly layered architecture. Despite the nuclear organization of the bird pallium, it has a cyto-architectonic organization that is reminiscent of the mammalian cortex.

Science, this issue p. eabc5534

Structured Abstract

INTRODUCTION

For more than a century, the avian forebrain has been a riddle for neuroscientists. Birds demonstrate exceptional cognitive abilities comparable to those of mammals, but their forebrain organization is radically different. Whereas mammalian cognition emerges from the canonical circuits of the six-layered neocortex, the avian forebrain seems to display a simple nuclear organization. Only one of these nuclei, the Wulst, has been generally accepted to be homologous to the neocortex. Most of the remaining pallium is constituted by a multinuclear structure called the dorsal ventricular ridge (DVR), which has no direct counterpart in mammals. Nevertheless, one long-standing theory, along with recent scientific evidence, supports the idea that some parts of the sensory DVR could display connectivity patterns, physiological signatures, and cell type–specific markers that are reminiscent of the neocortex. However, it remains unknown if the entire Wulst and sensory DVR harbor a canonical circuit that structurally resembles mammalian cortical organization.

RATIONALE

The mammalian neocortex comprises a columnar and laminar organization with orthogonally organized fibers that run in radial and tangential directions. These fibers constitute repetitive canonical circuits as computational units that process information along the radial domain and associate it tangentially. In this study, we first analyzed the pallial fiber architecture with three-dimensional polarized light imaging (3D-PLI) in pigeons and subsequently reconstructed local sensory circuits of the Wulst and the sensory DVR in pigeons and barn owls by means of in vivo or in vitro applications of neuronal tracers. We focused on two distantly related bird species to prove the hypothesis that a canonical circuit comparable to the neocortex is a genuine feature of the avian sensory forebrain.

RESULTS

The 3D-PLI fiber analysis showed that both the Wulst and the sensory DVR display an orthogonal organization of radially and tangentially organized fibers along their entire extent. In contrast, nonsensory components of the DVR displayed a complex mosaic-like arrangement with patches of fibers with different orientations. Fiber tracing revealed an iterative circuit motif that was present across modalities (somatosensory, visual, and auditory), brain regions (sensory DVR and Wulst), and species (pigeon and barn owl). Although both species showed a comparable column- and lamina-like circuit organization, small species differences were discernible, particularly for the Wulst, which was more subdifferentiated in barn owls, which fits well with the processing of stereopsis, combined with high visual acuity in the Wulst of this species. The primary sensory zones of the DVR were tightly interconnected with the intercalated nidopallial layers and the overlying mesopallium. In addition, nidopallial and some hyperpallial lamina-like areas gave rise to long-range tangential projections connecting sensory, associative, and motor structures.

CONCLUSION

Our study reveals a hitherto unknown neuroarchitecture of the avian sensory forebrain that is composed of iteratively organized canonical circuits within tangentially organized lamina-like and orthogonally positioned column-like entities. Our findings suggest that it is likely that an ancient microcircuit that already existed in the last common stem amniote might have been evolutionarily conserved and partly modified in birds and mammals. The avian version of this connectivity blueprint could conceivably generate computational properties reminiscent of the neocortex and would thus provide a neurobiological explanation for the comparable and outstanding perceptual and cognitive feats that occur in both taxa.

Fiber architectures of mammalian and avian forebrains.

Schematic drawings of a rat brain (left) and a pigeon brain (right) depict their overall pallial organization. The mammalian dorsal pallium harbors the six-layered neocortex with a granular input layer IV (purple) and supra- and infragranular layers II/III and V/VI, respectively (blue). The avian pallium comprises the Wulst and the DVR, which both, at first glance, display a nuclear organization. Their primary sensory input zones are shown in purple, comparable to layer IV. According to this study, both mammals and birds show an orthogonal fiber architecture constituted by radially (dark blue) and tangentially (white) oriented fibers. Tangential fibers associate distant pallial territories. Whereas this pattern dominates the whole mammalian neocortex, in birds, only the sensory DVR and the Wulst (light green) display such an architecture, and the associative and motor areas (dark green), as in the caudal DVR, are devoid of this cortex-like fiber architecture. NC, caudal nidopallium.

3D RAT BRAIN (LEFT): SCALABLE BRAIN ATLAS, RESEARCH RESOURCE IDENTIFIER (RRID) SCR_006934

Abstract

Although the avian pallium seems to lack an organization akin to that of the cerebral cortex, birds exhibit extraordinary cognitive skills that are comparable to those of mammals. We analyzed the fiber architecture of the avian pallium with three-dimensional polarized light imaging and subsequently reconstructed local and associative pallial circuits with tracing techniques. We discovered an iteratively repeated, column-like neuronal circuitry across the layer-like nuclear boundaries of the hyperpallium and the sensory dorsal ventricular ridge. These circuits are connected to neighboring columns and, via tangential layer-like connections, to higher associative and motor areas. Our findings indicate that this avian canonical circuitry is similar to its mammalian counterpart and might constitute the structural basis of neuronal computation.

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Science

Too bright to breed

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Night light from coastal cities overpowers natural signals for coral spawning from neighboring reefs.

PHOTO: NOKURO/ALAMY STOCK PHOTO

Most coral species reproduce through broadcast spawning. For such a strategy to be successful, coordination has had to evolve such that gametes across clones are released simultaneously. Over millennia, lunar cycles have facilitated this coordination, but the recent development of bright artificial light has led to an overpowering of these natural signals. Ayalon et al. tested for the direct impact of different kinds of artificial light on different species of corals. The authors found that multiple lighting types, including cold and warm light-emitting diode (LED) lamps, led to loss of synchrony and spawning failure. Further, coastal maps of artificial lighting globally suggest that it threatens to interfere with coral reproduction worldwide and that the deployment of LED lights, the blue light of which penetrates deeper into the water column, is likely to make the situation even worse.

Curr. Biol. 10.1016/j.cub.2020.10.039 (2020).

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SpaceX launches Starlink app and provides pricing and service info to early beta testers

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SpaceX has debuted an official app for its Starlink satellite broadband internet service, for both iOS and Android devices. The Starlink app allows users to manage their connection – but to take part you’ll have to be part of the official beta program, and the initial public rollout of that is only just about to begin, according to emails SpaceX sent to potential beta testers this week.

The Starlink app provides guidance on how to install the Starlink receiver dish, as well as connection status (including signal quality), a device overview for seeing what’s connected to your network, and a speed test tool. It’s similar to other mobile apps for managing home wifi connections and routers. Meanwhile, the emails to potential testers that CNBC obtained detail what users can expect in terms of pricing, speeds and latency.

The initial Starlink public beta test is called the “Better than Nothing Beta Program,” SpaceX confirms in their app description, and will be rolled out across the U.S. and Canada before the end of the year – which matches up with earlier stated timelines. As per the name, SpaceX is hoping to set expectations for early customers, with speeds users can expect ranging from between 50Mb/s to 150Mb/s, and latency of 20ms to 40ms according to the customer emails, with some periods including no connectivity at all. Even with expectations set low, if those values prove accurate, it should be a big improvement for users in some hard-to-reach areas where service is currently costly, unreliable and operating at roughly dial-up equivalent speeds.

Image Credits: SpaceX

In terms of pricing, SpaceX says in the emails that the cost for participants in this beta program will be $99 per moth, plus a one-time cost of $499 initially to pay for the hardware, which includes the mounting kit and receiver dish, as well as a router with wifi networking capabilities.

The goal eventually is offer reliably, low-latency broadband that provides consistent connection by handing off connectivity between a large constellation of small satellites circling the globe in low Earth orbit. Already, SpaceX has nearly 1,000 of those launched, but it hopes to launch many thousands more before it reaches global coverage and offers general availability of its services.

SpaceX has already announced some initial commercial partnerships and pilot programs for Starlink, too, including a team-up with Microsoft to connect that company’s mobile Azure data centers, and a project with an East Texas school board to connect the local community.

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Erratum for the Report “Meta-analysis reveals declines in terrestrial but increases in freshwater insect abundances” by R. Van Klink, D. E. Bowler, K. B. Gongalsky, A. B. Swengel, A. Gentile, J. M. Chase

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S. Rennie, J. Adamson, R. Anderson, C. Andrews, J. Bater, N. Bayfield, K. Beaton, D. Beaumont, S. Benham, V. Bowmaker, C. Britt, R. Brooker, D. Brooks, J. Brunt, G. Common, R. Cooper, S. Corbett, N. Critchley, P. Dennis, J. Dick, B. Dodd, N. Dodd, N. Donovan, J. Easter, M. Flexen, A. Gardiner, D. Hamilton, P. Hargreaves, M. Hatton-Ellis, M. Howe, J. Kahl, M. Lane, S. Langan, D. Lloyd, B. McCarney, Y. McElarney, C. McKenna, S. McMillan, F. Milne, L. Milne, M. Morecroft, M. Murphy, A. Nelson, H. Nicholson, D. Pallett, D. Parry, I. Pearce, G. Pozsgai, A. Riley, R. Rose, S. Schafer, T. Scott, L. Sherrin, C. Shortall, R. Smith, P. Smith, R. Tait, C. Taylor, M. Taylor, M. Thurlow, A. Turner, K. Tyson, H. Watson, M. Whittaker, I. Woiwod, C. Wood, UK Environmental Change Network (ECN) Moth Data: 1992-2015, NERC Environmental Information Data Centre (2018); .

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