Editing Brain (section)

=== Invertebrates ===
[[Image:Drosophila melanogaster - side (aka).jpg|thumb|right|alt=A fly resting on a reflective surface. A large, red eye faces the camera. The body appears transparent, apart from black pigment at the end of its abdomen. |Fruit flies (''[[Drosophila]]'') have been extensively studied to gain insight into the role of genes in brain development.]]
This category includes [[tardigrade]]s, [[arthropod]]s, [[Mollusca|molluscs]], and numerous types of worms. The diversity of invertebrate body plans is matched by an equal diversity in brain structures.<ref>{{cite book |last=Barnes |first=RD |title=Invertebrate Zoology |year=1987 |edition=5th |page=1 |publisher=Saunders College Pub. |isbn=978-0-03-008914-5}}</ref>

Two groups of invertebrates have notably complex brains: arthropods (insects, [[crustacean]]s, [[arachnid]]s, and others), and [[cephalopod]]s (octopuses, [[squid]]s, and similar molluscs).<ref name=Butler>{{cite journal |last=Butler |first=AB |title=Chordate Evolution and the Origin of Craniates: An Old Brain in a New Head |journal=Anatomical Record |year=2000 |volume=261 |pages=111–125 |pmid=10867629 |doi=10.1002/1097-0185(20000615)261:3<111::AID-AR6>3.0.CO;2-F |issue=3|doi-access=free }}</ref> The brains of arthropods and cephalopods arise from twin parallel nerve cords that extend through the body of the animal. Arthropods have a central brain, the [[supraesophageal ganglion]], with three divisions and large [[optic lobe (arthropod)|optical lobes]] behind each eye for visual processing.<ref name=Butler/> Cephalopods such as the octopus and squid have the largest brains of any invertebrates.<ref name="Bulloch1995">{{cite book |last1=Bulloch |first1=TH |editor=Breidbach O |last2=Kutch |first2=W |title=The nervous systems of invertebrates: an evolutionary and comparative approach |chapter-url=https://books.google.com/books?id=dW5e6FHOH-4C&pg=PA439 |year=1995 |publisher=Birkhäuser |isbn=978-3-7643-5076-5 |page=439 |chapter=Are the main grades of brains different principally in numbers of connections or also in quality?}}</ref>

There are several invertebrate species whose brains have been studied intensively because they have properties that make them convenient for experimental work:
* Fruit flies (''Drosophila''), because of the large array of techniques available for studying their [[genetics]], have been a natural subject for studying the role of genes in brain development.<ref>{{cite web |title=Flybrain: An online atlas and database of the ''drosophila'' nervous system |url=http://flybrain.neurobio.arizona.edu| archive-url=https://web.archive.org/web/19980109184708/http://flybrain.neurobio.arizona.edu/| url-status=dead| archive-date=1998-01-09 |access-date=2011-10-14}}</ref> In spite of the large evolutionary distance between insects and mammals, many aspects of ''Drosophila'' [[neurogenetics]] have been shown to be relevant to humans. The first biological [[clock gene]]s, for example, were identified by examining ''Drosophila'' mutants that showed disrupted daily activity cycles.<ref>{{cite journal |year=1971 |title=Clock Mutants of Drosophila melanogaster |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=68 |pages=2112–2116 |pmid=5002428 |doi=10.1073/pnas.68.9.2112 |pmc=389363 |last1=Konopka |first1=RJ |last2=Benzer |first2=S |issue=9 |bibcode=1971PNAS...68.2112K|doi-access=free }}</ref> A search in the genomes of vertebrates revealed a set of analogous genes, which were found to play similar roles in the mouse biological clock—and therefore almost certainly in the human biological clock as well.<ref>{{cite journal|last1=Shin|first1=Hee-Sup|last2=Bargiello|first2=Thaddeus A.|last3=Clark|first3=Brian T.|last4=Jackson|first4=F. Rob|last5=Young|first5=Michael W.|display-authors=1|year=1985|title=An unusual coding sequence from a Drosophila clock gene is conserved in vertebrates|url=https://pubmed.ncbi.nlm.nih.gov/2413365/|journal=Nature|volume=317|issue=6036|pages=445–448|bibcode=1985Natur.317..445S|doi=10.1038/317445a0|pmid=2413365 |s2cid=4372369}}</ref> Studies done on Drosophila, also show that most [[neuropil]] regions of the brain are continuously reorganized throughout life in response to specific living conditions.<ref>{{cite journal |last1=Heisenberg |first1=M |last2=Heusipp |first2=M |last3=Wanke |first3=C. |year=1995 |title=Structural plasticity in the Drosophila brain |journal=J. Neurosci. |volume=15 |issue=3 |pages=1951–1960|doi=10.1523/JNEUROSCI.15-03-01951.1995 |pmid=7891144 |pmc=6578107 |doi-access=free }}</ref>
* The nematode worm ''[[Caenorhabditis elegans]]'', like ''Drosophila'', has been studied largely because of its importance in genetics.<ref>{{Cite journal|last=Brenner|first=Sydney|year=1974|title=The Genetics of CAENORHABDITIS ELEGANS|journal= Genetics|volume=77|issue=1|pages=71–94|doi=10.1093/genetics/77.1.71|pmid=4366476|pmc=1213120}}</ref> In the early 1970s, [[Sydney Brenner]] chose it as a [[model organism]] for studying the way that genes control development. One of the advantages of working with this worm is that the body plan is very stereotyped: the nervous system of the [[hermaphrodite]] contains exactly 302 neurons, always in the same places, making identical synaptic connections in every worm.<ref>{{Cite journal |title=Specification of the nervous system |last=Hobert |first=O |editor=The ''C. elegans'' Research Community |year=2005 |doi=10.1895/wormbook.1.12.1 |url=http://www.wormbook.org/chapters/www_specnervsys/specnervsys.html |journal=WormBook |pmid=18050401 |pages=1–19|pmc=4781215 }}</ref> Brenner's team sliced worms into thousands of ultrathin sections and photographed each one under an electron microscope, then visually matched fibers from section to section, to map out every neuron and synapse in the entire body.<ref>{{cite journal |year=1986 |title=The Structure of the Nervous System of the Nematode Caenorhabditis elegans |journal=[[Philosophical Transactions of the Royal Society B]] |volume=314 |pages=1–340 |doi=10.1098/rstb.1986.0056 |last1=White |first1=JG |last2=Southgate |first2=E |author-link2=Eileen Southgate |last3=Thomson |first3=JN |last4=Brenner |first4=S |issue=1165 |pmid=22462104 |bibcode=1986RSPTB.314....1W }}</ref> The complete neuronal ''wiring diagram'' of ''C.elegans'' – its [[connectome]] was achieved.<ref>{{cite web |last=Jabr |first=Ferris |date=2012-10-02 |title=The Connectome Debate: Is Mapping the Mind of a Worm Worth It? |url=http://www.scientificamerican.com/article.cfm?id=c-elegans-connectome |work=Scientific American |access-date=2014-01-18}}</ref> Nothing approaching this level of detail is available for any other organism, and the information gained has enabled a multitude of studies that would otherwise have not been possible.<ref>{{cite book |chapter=''Caenorhabditis elegans'' |last=Hodgkin |first=J |title=Encyclopedia of Genetics |veditors=Brenner S, Miller JH |publisher=Elsevier |year=2001 |pages=251–256 |isbn=978-0-12-227080-2}}</ref>
* The sea slug ''[[Aplysia]] californica'' was chosen by Nobel Prize-winning neurophysiologist [[Eric Kandel]] as a model for studying the cellular basis of [[learning]] and [[memory]], because of the simplicity and accessibility of its nervous system, and it has been examined in hundreds of experiments.<ref>{{cite book |last=Kandel |first=ER |title=In Search of Memory: The Emergence of a New Science of Mind |year=2007 |publisher=WW Norton |isbn=978-0-393-32937-7 |pages=[https://archive.org/details/insearchofmemory0000kand/page/145 145–150] |url=https://archive.org/details/insearchofmemory0000kand/page/145 }}</ref>