The dragon sleeps tonight: Most animal species sleep, from invertebrates to primates. However, neuroscientists have until now only actively recorded the sleeping brains of birds and mammals. Shein-Idelson et al. now describe the electrophysiological hallmarks of sleep in reptiles. Recordings from the brains of Australian dragons revealed the typical features of slow-wave sleep and rapid eye movement (REM) sleep. These findings indicate that the brainstem circuits responsible for slow-wave and REM sleep are not only very ancient but were already involved in sleep dynamics in reptiles. Science , this issue p. 590

A Primer on the reptile brain, in particular the light it sheds on the structural and functional evolution of vertebrate neural circuits.

Some 320 million years ago (MYA), the evolution of a protective membrane surrounding the embryo, the amnion, enabled vertebrates to develop outside water and thus invade new terrestrial niches. These amniotes were the ancestors of today’s mammals and sauropsids (reptiles and birds). Present-day reptiles are a diverse group of more than 10,000 species that comprise the sphenodon, lizards, snakes, turtles and crocodilians. Although turtles were once thought to be the most “primitive” among the reptiles, current genomic data point toward two major groupings: the Squamata (lizards and snakes) and a group comprising both the turtles and the Archosauria (dinosaurs and modern birds and crocodiles). Dinosaurs inhabited the Earth from the Triassic (230 MYA), at a time when the entire landmass formed a single Pangaea. Dinosaurs flourished from the beginning of the Jurassic to the mass extinction at the end of the Cretaceous (65 MYA), and birds are their only survivors. What people generally call reptiles is thus a group defined in part by exclusion: it gathers amniote species that are neither mammals nor birds, making the reptiles technically a paraphyletic grouping. Despite this, the so-defined reptiles share many evolutionary, anatomical, developmental, physiological (e.g., ectothermia), and functional features. It is thus reasonable to talk about a “reptilian brain.”

Objective . Chronic neural recordings have provided many insights into the relationship between neural activity and behavior. We set out to develop a miniaturized motorized microdrive that allows precise electrode positioning despite possibly unreliable motors. Approach . We designed a feedback-based motor control mechanism. It contains an integrated position readout from an array of magnets and a Hall sensor. Main results . Our extremely lightweight (<1 g) motorized microdrive allows remote positioning of both metal electrodes and glass pipettes along one motorized axis. Target locations can be defined with a range of 6 mm and they can be reached within 1 µ m precision. The incorporated headstage electronics are capable of both extracellular and intracellular recordings. We include a simple mechanism for repositioning electrodes in three dimensions and for replacing them during operation. We present neural data from different premotor areas of adult and juvenile zebra finches. Significance . Our findings show that feedback-based microdrive control requires little extra size and weight, suggesting that such control can be incorporated into more complex multi-electrode designs.

Many potentially noxious interventions are performed on chicken embryos in research and in the poultry industry. It is therefore essential and in the interest of animal welfare to be able to precisely define the point at which a chicken embryo is capable of nociception in ovo. The present part III of a comprehensive study examined the movements of developing chicken embryos with the aim of identifying behavioral responses to a noxious stimulus. For this purpose, a noxious mechanical stimulus and a control stimulus were applied in a randomized order. The recorded movements of the embryos were evaluated using the markerless pose estimation software DeepLabCut and manual observations. After the application of the mechanical stimulus, a significant increase in beak movement was identified in 15- to 18-day-old embryos. In younger embryos, no behavioral changes related to the noxious stimulus were observed. The presented results indicate that noxious mechanical stimuli at the beak base evoke a nocifensive reaction in chicken embryos starting at embryonic day 15.