The ''Drosophila'' connectome, once completed, will be a complete list of the roughly 135,000

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

s in the brain of the fruit fly ''

Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the "vinegar fly" or "pomace fly". Starting with Ch ...

'', along with all of the connections (

synapse In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell. Synapses are essential to the transmission of nervous impulses from ...

s) between these neurons. As of 2020, the ''Drosophila'' connectome is a work in progress, being obtained by the methods of

neural circuit reconstruction Neural circuit reconstruction is the reconstruction of the detailed circuitry of the nervous system (or a portion of the nervous system) of an animal. It is sometimes called EM reconstruction since the main method used is the electron microscope (E ...

. A stack of EM images of an entire brain exist, suitable for sparse tracing of specific circuits. A full connectome of a large portion of the central brain is likewise available. Many of the 76 compartments of the ''Drosophila'' brain have connectomes available, and the remainders are subjects of ongoing study.

Why ''Drosophila''

Connectome A connectome () is a comprehensive map of neural connections in the brain, and may be thought of as its "wiring diagram". An organism's nervous system is made up of neurons which communicate through synapses. A connectome is constructed by tr ...

research (

connectomics Connectomics is the production and study of connectomes: comprehensive maps of connections within an organism's nervous system. More generally, it can be thought of as the study of neuronal wiring diagrams with a focus on how structural connectivi ...

) has a number of competing objectives. On the one hand, investigators prefer an organism small enough that the connectome can be obtained in a reasonable amount of time. This argues for a small creature. On the other hand, one of the main uses of a connectome is to relate structure and behavior, so an animal with a large behavioral repertoire is desirable. It's also very helpful to use an animal with a large existing community of experimentalists, and many available genetic tools. ''Drosophila'' looks very good on these counts: *The brain contains about 135,000 neurons, small enough to be reconstructed in the near future. *The fruit fly exhibits many complex behaviors. Hundreds of different behaviors (feeding, grooming, flying, mating, learning, and so on) have been qualitatively and quantitatively studied over the years. *The genetics of the fruit fly are well understood, and many (tens of thousands) of genetic variants are available. *There are many electrophysiological,

calcium imaging Calcium imaging is a microscopy technique to optically measure the calcium (Ca2+) status of an isolated cell, tissue or medium. Calcium imaging takes advantage of calcium indicators, fluorescent molecules that respond to the binding of Ca2+ ions ...

, and other studies ongoing with ''Drosophila''.

Current status

A high-level connectome, at the level of brain compartments and interconnecting tracts of neurons, exists for the full fly brain. A version of this is available online. Detailed circuit-level connectomes exist for the

lamina Lamina may refer to: Science and technology * Planar lamina, a two-dimensional planar closed surface with mass and density, in mathematics * Laminar flow, (or streamline flow) occurs when a fluid flows in parallel layers, with no disruption betwee ...

and a

medulla Medulla or Medullary may refer to: Science * Medulla oblongata, a part of the brain stem * Renal medulla, a part of the kidney * Adrenal medulla, a part of the adrenal gland * Medulla of ovary, a stroma in the center of the ovary * Medulla of t ...

column, both in the visual system of the fruit fly, and the alpha lobe of the mushroom body. In May of 2017 a paper published in bioRxiv presented an electron microscopy image stack of the whole adult female brain at synaptic resolution. The volume is available for sparse tracing of selected circuits. In 2020, a dense connectome of half the central brain of ''Drosophila'' was released, along with a web site that allows queries and exploration of this data. The methods used in reconstruction and initial analysis of the connectome followed. A natural question is whether the connectome will allow simulation of the fly's behavior. However, the connectome alone is not sufficient. Additional information needed includes

gap junction Gap junctions are specialized intercellular connections between a multitude of animal cell-types. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulate ...

varieties and locations, identities of

neurotransmitters A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell. Neur ...

, receptor types and locations,

neuromodulators Neuromodulation is the physiological process by which a given neuron uses one or more chemicals to regulate diverse populations of neurons. Neuromodulators typically bind to metabotropic, G-protein coupled receptors (GPCRs) to initiate a second m ...

and

hormones A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and beh ...

(with sources and receptors), the role of

glial cells Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system that do not produce electrical impulses. They maintain homeostasis, form mye ...

, time evolution rules for synapses, and more.

References

External links

FlyCircuit DatabaseFruit Fly Brain Observatory
Brain Emerging technologies Neural coding Neuroimaging Neuroinformatics Drosophila melanogaster Invertebrate nervous system

Why ''Drosophila''

Current status

See also

References

Further reading

External links