A connectome and analysis of the adult Drosophila central brain.

The neural circuits responsible for animal behavior remain largely unknown. We summarize new methods and present the circuitry of a large fraction of the brain of the fruit fly Drosophila melanogaster. Improved methods include new procedures to prepare, image, align, segment, find synapses in, and proofread such large data sets. We define cell types, refine computational compartments, and provide an exhaustive atlas of cell examples and types, many of them novel. We provide detailed circuits consisting of neurons and their chemical synapses for most of the central brain. We make the data public and simplify access, reducing the effort needed to answer circuit questions, and provide procedures linking the neurons defined by our analysis with genetic reagents. Biologically, we examine distributions of connection strengths, neural motifs on different scales, electrical consequences of compartmentalization, and evidence that maximizing packing density is an important criterion in the evolution of the fly's brain.

Animal brains of all sizes, from the smallest to the largest, work in broadly similar ways. Studying the brain of any one animal in depth can thus reveal the general principles behind the workings of all brains. The fruit fly Drosophila is a popular choice for such research. With about 100,000 neurons ­ compared to some 86 billion in humans ­ the fly brain is small enough to study at the level of individual cells. But it nevertheless supports a range of complex behaviors, including navigation, courtship and learning. Thanks to decades of research, scientists now have a good understanding of which parts of the fruit fly brain support particular behaviors. But exactly how they do this is often unclear. This is because previous studies showing the connections between cells only covered small areas of the brain. This is like trying to understand a novel when all you can see is a few isolated paragraphs. To solve this problem, Scheffer, Xu, Januszewski, Lu, Takemura, Hayworth, Huang, Shinomiya et al. prepared the first complete map of the entire central region of the fruit fly brain. The central brain consists of approximately 25,000 neurons and around 20 million connections. To prepare the map ­ or connectome ­ the brain was cut into very thin 8nm slices and photographed with an electron microscope. A three-dimensional map of the neurons and connections in the brain was then reconstructed from these images using machine learning algorithms. Finally, Scheffer et al. used the new connectome to obtain further insights into the circuits that support specific fruit fly behaviors. The central brain connectome is freely available online for anyone to access. When used in combination with existing methods, the map will make it easier to understand how the fly brain works, and how and why it can fail to work correctly. Many of these findings will likely apply to larger brains, including our own. In the long run, studying the fly connectome may therefore lead to a better understanding of the human brain and its disorders. Performing a similar analysis on the brain of a small mammal, by scaling up the methods here, will be a likely next step along this path.

Physiologic Correlates of Interactions between Adult Male and Immature Long-tailed Macaques (Macaca fascicularis).

Interactions between adult males and immature members of the same species are rare in most mammals; in contrast, an estimated 40% of primate species are characterized by an involvement of males in the social life of infants and juveniles. The proximate mechanisms of male-infant interactions are largely unstudied, and very few direct benefits for males have been proposed, especially in uniparental species in which the identity of the male parent is uncertain. In this study, we aimed to assess the relationship among behavioral and physiologic stress, health, and various affiliative behaviors initiated by adult males toward infants and juveniles in long-tailed macaques. We hypothesized that males that spent more time with infants and juveniles would have lower physiologic and social stress and better health than males with less interaction. We observed 2 troops of macaques with established social hierarchies (n = 18 in troop 1 and n = 8 in troop 2), each occupying a stable area within the enclosure, for more than 200 h. Fecal samples were used to assess cortisol levels as a measure of physiologic stress, and blood samples were collected to measure oxytocin levels as an index of social responsiveness. Our results indicated that male affiliative behavior directed toward immature animals was significantly higher in the troop characterized by more social conflicts; midranking males interacted more with infants than high- and low-ranking males in both troops. Furthermore, the DHEA:cortisol ratio, a physiologic index of resilience and coping, was positively correlated with males' affiliative responses, suggesting a neuroprotective role of male-infant interactions. In summary, our data support a proximate mechanism of alloparenting or paternal behavior in uniparental species. Interacting with infants and juveniles could provide an immediate neurobiologic benefit to adult males by facilitating adaptive coping responses to social tensions.