Editing Brain (section)

=== History ===
{{See also|History of neuroscience}}
[[File:Descartes-reflex.JPG|thumb|right|Illustration by [[René Descartes]] of how the brain implements a reflex response]]

The oldest brain to have been discovered was in [[Armenia]] in the [[Areni-1 cave complex]]. The brain, estimated to be over 5,000 years old, was found in the skull of a 12 to 14-year-old girl. Although the brains were shriveled, they were well preserved due to the climate found inside the cave.<ref>{{cite news|last1=Bower|first1=Bruce|date=2009-01-12|title=Armenian cave yields ancient human brain |agency=ScienceNews|url=https://www.sciencenews.org/article/armenian-cave-yields-ancient-human-brain|url-access=registration|access-date=2021-01-23}}</ref>

Early philosophers were divided as to whether the seat of the soul lies in the brain or heart. [[Aristotle]] favored the heart, and thought that the function of the brain was merely to cool the blood. [[Democritus]], the inventor of the atomic theory of matter, argued for a three-part soul, with intellect in the head, emotion in the heart, and lust near the liver.<ref name="Finger14">{{cite book|last=Finger|first=Stanley|title=Origins of Neuroscience|publisher=Oxford University Press|year=2001|isbn=978-0-19-514694-3|pages=14–15}}</ref> The unknown author of ''[[On the Sacred Disease]]'', a medical treatise in the [[Hippocratic Corpus]], came down unequivocally in favor of the brain, writing:

{{blockquote|Men ought to know that from nothing else but the brain come joys, delights, laughter and sports, and sorrows, griefs, despondency, and lamentations. ... And by the same organ we become mad and delirious, and fears and terrors assail us, some by night, and some by day, and dreams and untimely wanderings, and cares that are not suitable, and ignorance of present circumstances, desuetude, and unskillfulness. All these things we endure from the brain, when it is not healthy...|''On the Sacred Disease'', attributed to [[Hippocrates]]<ref name=Hippocrates>{{Citation |author=Hippocrates |title=On the Sacred Disease |year=2006 |orig-year=400 BCE |translator=Francis Adams |publisher=((Internet Classics Archive: The University of Adelaide Library)) |url=http://etext.library.adelaide.edu.au/mirror/classics.mit.edu/Hippocrates/sacred.html |archive-url=https://web.archive.org/web/20070926213032/http://etext.library.adelaide.edu.au/mirror/classics.mit.edu/Hippocrates/sacred.html |archive-date=September 26, 2007}}</ref>}}

[[File:1543, Andreas Vesalius' Fabrica, Base Of The Brain.jpg|thumb|left|upright|[[Andreas Vesalius]]' ''Fabrica'', published in 1543, showing the base of the human brain, including [[optic chiasm]]a, cerebellum, [[olfactory bulb]]s, etc.]]

The Roman physician [[Galen]] also argued for the importance of the brain, and theorized in some depth about how it might work. Galen traced out the anatomical relationships among brain, nerves, and muscles, demonstrating that all muscles in the body are connected to the brain through a branching network of nerves. He postulated that nerves activate muscles mechanically by carrying a mysterious substance he called ''pneumata psychikon'', usually translated as "animal spirits".<ref name=Finger14/> Galen's ideas were widely known during the Middle Ages, but not much further progress came until the Renaissance, when detailed anatomical study resumed, combined with the theoretical speculations of [[René Descartes]] and those who followed him. Descartes, like Galen, thought of the nervous system in hydraulic terms. He believed that the highest cognitive functions are carried out by a non-physical ''res cogitans'', but that the majority of behaviors of humans, and all behaviors of animals, could be explained mechanistically.<ref name="Finger14" />

The first real progress toward a modern understanding of nervous function, though, came from the investigations of [[Luigi Galvani]] (1737–1798), who discovered that a shock of static electricity applied to an exposed nerve of a dead frog could cause its leg to contract. Since that time, each major advance in understanding has followed more or less directly from the development of a new technique of investigation. Until the early years of the 20th century, the most important advances were derived from new methods for [[staining]] cells.<ref>{{cite book |last=Bloom |first=FE |veditors=Schmidt FO, Worden FG, Swazey JP, Adelman G |title=The Neurosciences, Paths of Discovery |publisher=MIT Press |year=1975 |isbn=978-0-262-23072-8 |page=[https://archive.org/details/TheNeurosc_00_Word/page/211 211] |url=https://archive.org/details/TheNeurosc_00_Word/page/211 }}</ref> Particularly critical was the invention of the [[Golgi's method|Golgi stain]], which (when correctly used) stains only a small fraction of neurons, but stains them in their entirety, including cell body, dendrites, and axon. Without such a stain, brain tissue under a microscope appears as an impenetrable tangle of protoplasmic fibers, in which it is impossible to determine any structure. In the hands of [[Camillo Golgi]], and especially of the Spanish neuroanatomist [[Santiago Ramón y Cajal]], the new stain revealed hundreds of distinct types of neurons, each with its own unique dendritic structure and pattern of connectivity.<ref>{{cite book |title=Foundations of the Neuron Doctrine |last=Shepherd |first=GM |year=1991 |publisher=Oxford University Press |isbn=978-0-19-506491-9 |chapter=Ch.1 : Introduction and Overview}}</ref>

[[File:PurkinjeCell.jpg|thumb|right|alt=A drawing on yellowing paper with an archiving stamp in the corner. A spidery tree branch structure connects to the top of a mass. A few narrow processes follow away from the bottom of the mass.|Drawing by [[Santiago Ramón y Cajal]] of two types of Golgi-stained neurons from the cerebellum of a pigeon]]

In the first half of the 20th century, advances in electronics enabled investigation of the electrical properties of nerve cells, culminating in work by [[Alan Lloyd Hodgkin|Alan Hodgkin]], [[Andrew Huxley]], and others on the biophysics of the action potential, and the work of [[Bernard Katz]] and others on the electrochemistry of the synapse.<ref>{{cite journal |last=Piccolino |first=M |year=2002 |title=Fifty years of the Hodgkin-Huxley era |journal=Trends in Neurosciences |volume=25 |pages=552–553 |pmid=12392928 |doi=10.1016/S0166-2236(02)02276-2 |issue=11|s2cid=35465936 }}</ref> These studies complemented the anatomical picture with a conception of the brain as a dynamic entity. Reflecting the new understanding, in 1942 [[Charles Scott Sherrington|Charles Sherrington]] visualized the workings of the brain waking from sleep:

{{blockquote|The great topmost sheet of the mass, that where hardly a light had twinkled or moved, becomes now a sparkling field of rhythmic flashing points with trains of traveling sparks hurrying hither and thither. The brain is waking and with it the mind is returning. It is as if the Milky Way entered upon some cosmic dance. Swiftly the head mass becomes an enchanted loom where millions of flashing shuttles weave a dissolving pattern, always a meaningful pattern though never an abiding one; a shifting harmony of subpatterns.|Sherrington, 1942, ''Man on his Nature''<ref>{{cite book |last=Sherrington |first=CS |title=Man on his nature |date=2000 |orig-date=1942 |publisher=Cambridge University Press |page=[https://archive.org/details/isbn_9780838577011/page/178 178] |isbn=978-0-8385-7701-1 |url=https://archive.org/details/isbn_9780838577011/page/178 }}</ref>}}

The invention of electronic computers in the 1940s, along with the development of mathematical [[information theory]], led to a realization that brains can potentially be understood as information processing systems. This concept formed the basis of the field of [[cybernetics]], and eventually gave rise to the field now known as [[computational neuroscience]].<ref name=CKS1993>{{cite book |chapter=What is computational neuroscience? |last1=Churchland |first1=PS |last2=Koch |first2=C |last3=Sejnowski |first3=TJ |title=Computational Neuroscience |pages=46–55 |editor=Schwartz EL |year=1993 |publisher=MIT Press |isbn=978-0-262-69164-2}}</ref> The earliest attempts at cybernetics were somewhat crude in that they treated the brain as essentially a digital computer in disguise, as for example in [[John von Neumann]]'s 1958 book, ''[[The Computer and the Brain]]''.<ref>{{cite book |title=The Computer and the Brain |year=2000 |publisher=Yale University Press |isbn=978-0-300-08473-3 |last1=von Neumann |first1=J |last2=Churchland |first2=PM |last3=Churchland |first3=PS |pages=xi–xxii |url=https://archive.org/details/computerbrain0000vonn }}</ref> Over the years, though, accumulating information about the electrical responses of brain cells recorded from behaving animals has steadily moved theoretical concepts in the direction of increasing realism.<ref name=CKS1993/>

One of the most influential early contributions was a 1959 paper titled ''What the frog's eye tells the frog's brain'': the paper examined the visual responses of neurons in the [[retina]] and [[superior colliculus|optic tectum]] of frogs, and came to the conclusion that some neurons in the tectum of the frog are wired to combine elementary responses in a way that makes them function as "bug perceivers".<ref>{{cite journal |title=What the frog's eye tells the frog's brain |journal=Proceedings of the Institute of Radio Engineers |volume=47 |issue=11 |pages=1940–1951 |year=1959 |url=http://jerome.lettvin.info/lettvin/Jerome/WhatTheFrogsEyeTellsTheFrogsBrain.pdf |last1=Lettvin |first1=JY |last2=Maturana |first2=HR |last3=McCulloch |first3=WS |last4=Pitts |first4=WH |doi=10.1109/jrproc.1959.287207 |s2cid=8739509 |url-status=dead |archive-url=https://web.archive.org/web/20110928024235/http://jerome.lettvin.info/lettvin/Jerome/WhatTheFrogsEyeTellsTheFrogsBrain.pdf |archive-date=2011-09-28 }}</ref> A few years later [[David H. Hubel|David Hubel]] and [[Torsten Wiesel]] discovered cells in the primary visual cortex of monkeys that become active when sharp edges move across specific points in the field of view—a discovery for which they won a Nobel Prize.<ref>{{cite book |title=Brain and visual perception: the story of a 25-year collaboration |url=https://archive.org/details/brainvisualperce00hube |url-access=limited |last1=Hubel |first1=DH |last2=Wiesel |first2=TN |publisher=Oxford University Press US |year=2005 |isbn=978-0-19-517618-6 |pages=[https://archive.org/details/brainvisualperce00hube/page/n665 657]–704}}</ref> Follow-up studies in higher-order visual areas found cells that detect [[binocular disparity]], color, movement, and aspects of shape, with areas located at increasing distances from the primary visual cortex showing increasingly complex responses.<ref>{{cite book |title=The Cognitive Neuroscience of Vision |last=Farah |first=MJ |year=2000 |publisher=Wiley-Blackwell |isbn=978-0-631-21403-8 |pages=1–29}}</ref> Other investigations of brain areas unrelated to vision have revealed cells with a wide variety of response correlates, some related to memory, some to abstract types of cognition such as space.<ref>{{cite journal |last1=Engel |first1=AK |last2=Singer |first2=W |title=Temporal binding and the neural correlates of sensory awareness |journal=Trends in Cognitive Sciences |year=2001 |volume=5 |pages=16–25 |pmid=11164732 |doi=10.1016/S1364-6613(00)01568-0 |issue=1|s2cid=11922975 }}</ref>

Theorists have worked to understand these response patterns by constructing mathematical [[Nervous system network models|models of neurons and neural networks]], which can be simulated using computers.<ref name=CKS1993/> Some useful models are abstract, focusing on the conceptual structure of neural algorithms rather than the details of how they are implemented in the brain; other models attempt to incorporate data about the biophysical properties of real neurons.<ref>{{cite book |last1=Dayan |first1=P |last2=Abbott |first2=LF |title=Theoretical Neuroscience |chapter=Ch.7: Network models |year=2005 |publisher=MIT Press |isbn=978-0-262-54185-5}}</ref> No model on any level is yet considered to be a fully valid description of brain function, though. The essential difficulty is that sophisticated computation by neural networks requires distributed processing in which hundreds or thousands of neurons work cooperatively—current methods of brain activity recording are only capable of isolating action potentials from a few dozen neurons at a time.<ref>{{cite journal |last1=Averbeck |first1=BB |last2=Lee |first2=D |title=Coding and transmission of information by neural ensembles |journal=Trends in Neurosciences |year=2004 |volume=27 |pages=225–230 |pmid=15046882 |doi=10.1016/j.tins.2004.02.006 |issue=4|s2cid=44512482 }}</ref>

Furthermore, even single neurons appear to be complex and capable of performing computations.<ref>{{cite journal |author=Forrest, MD |title=Intracellular Calcium Dynamics Permit a Purkinje Neuron Model to Perform Toggle and Gain Computations Upon its Inputs. |journal=Frontiers in Computational Neuroscience |volume=8 |pages=86 |year=2014 |doi=10.3389/fncom.2014.00086 |pmid=25191262 |pmc=4138505|doi-access=free }}</ref> So, brain models that do not reflect this are too abstract to be representative of brain operation; models that do try to capture this are very computationally expensive and arguably intractable with present computational resources. However, the [[Human Brain Project]] is trying to build a realistic, detailed computational model of the entire human brain. The wisdom of this approach has been publicly contested, with high-profile scientists on both sides of the argument.

In the second half of the 20th century, developments in chemistry, electron microscopy, genetics, computer science, functional brain imaging, and other fields progressively opened new windows into brain structure and function. In the United States, the 1990s were officially designated as the "[[Decade of the Brain]]" to commemorate advances made in brain research, and to promote funding for such research.<ref>{{Cite journal |last1=Jones |first1=EG |last2=Mendell |first2=LM |year=1999 |title=Assessing the Decade of the Brain |journal=Science |volume=284 |issue=5415 |page=739 |bibcode=1999Sci...284..739J |doi=10.1126/science.284.5415.739|pmid=10336393|s2cid=13261978}}</ref>

In the 21st century, these trends have continued, and several new approaches have come into prominence, including [[multielectrode array|multielectrode recording]], which allows the activity of many brain cells to be recorded all at the same time;<ref>{{cite journal |last=Buzsáki |first=G |title=Large-scale recording of neuronal ensembles |journal=Nature Neuroscience |volume=7 |year=2004 |pages=446–451 |pmid=15114356 |url=http://osiris.rutgers.edu/BuzsakiHP/Publications/PDFs/Buzsaki2004NatNeurosci.pdf |archive-url=https://web.archive.org/web/20060910225619/http://osiris.rutgers.edu/BuzsakiHP/Publications/PDFs/Buzsaki2004NatNeurosci.pdf |url-status=dead |archive-date=2006-09-10 |doi=10.1038/nn1233 |issue=5|s2cid=18538341 }}</ref> [[genetic engineering]], which allows molecular components of the brain to be altered experimentally;<ref name=Tonegawa>{{cite journal |title=Genetic neuroscience of mammalian learning and memory |journal=[[Philosophical Transactions of the Royal Society B]] |year=2003 |volume=358 |pages=787–795 |pmid=12740125 |pmc=1693163 |last1=Tonegawa |first1=S |last2=Nakazawa |first2=K |last3=Wilson |first3=MA |doi=10.1098/rstb.2002.1243 |issue=1432}}</ref> [[genomics]], which allows variations in brain structure to be correlated with variations in [[DNA]] properties and [[neuroimaging]].<ref>{{cite journal |last1=Geschwind |first1=DH |last2=Konopka |first2=G |title=Neuroscience in the era of functional genomics and systems biology |journal=Nature |year=2009 |volume=461 |pages=908–915 |pmid=19829370 |doi=10.1038/nature08537 |issue=7266 |pmc=3645852 |bibcode=2009Natur.461..908G}}</ref>