Brains - Brains • • Materialistic definition of...

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Unformatted text preview: Brains • • Materialistic definition of brains o Brains are something made of neurons (a type of cell) o Plus all the associated brain chemistry (e.g., neurotransmitters) Materialist definition of neurons o Long cells that connect to each other and also to sensory cells and motor cells o Sensory cells Cells that react to activity in the environment o Motor cells (muscles) Groups of cells that can contract, allowing for movement • • • Functionalist definition of brains o The function of brains is to connect knowledge about the world to actions in the world, such that the actions promote our survival Functionalist definition of neurons o The function of neurons is to transmit information in such a way that knowledge about the world leads to effective behavior in the world Different types of (functionalist) brains • Brains without neurons o Plants Can follow the sun Catch flies ! ! ! ! Single cell organisms ! Single Eelao rganiAms eba (lives i n our intestines) c x l mpSe: s mell organisms o l ingle c o Example: Amoeba (lives in our intestines) ! Canmove ! Example: Amoeba (lives in our intestines) ! ! ! ! ! ! Can s ov e i an s vironheir t Can mense •theCr enense tmenenvironment Can ense •heiCan nd onprey and catch it y a sense m n Can ssensetprer envircatcheitt • • Can move ! ! CansenIss t pran cer a ca m ells ct ocally, there is no network for Can senn ehese gand ntdtchoiveaawlay e d ey ases he c t In !heCacasencoordinationndocalvy, away is no network for coordination t se n sesste e anglerac t l mo l e there h d cel s a In these cases the cells act locally, there is no network for coordination Can sense danger and move away ! ! ! ! Brains without thought ! wmple ho ni ht Brains Siithoutotrgaugsms ! Examporganis ra ! Simple le: Hydms(very tiny, lives in ponds) ! Exa! pNeuronsatr(ansly ttensy,nsvtis nninto movement in a very direct way m le: Hydr ver a i e li ae o i ponds) ! Hyd on transl en ory at lls int movement cel s very di uro w ! Neurra:smore satessensceionando movement inla than nerectns ay ! ! ! Huma : orp o n mr t l e l 00, d 0 cve nectt ce l e t r an or ons Hydra:nmape rsexisoayecyl1s an00moonmening lns uhonsnfeurevery sensory neuron Human: approximately 100,000 connecting neurons for every sensory neuron • Brains without thought o Simple organisms o Example: Hydra (very tiny, lives in ponds) Neurons translate sensation into movement in a very direct way Hydra: more sensory cells and movement cells than neurons Human: approximately 100,000 connecting neurons for every sensory neuron ! ! Human brains • ! ! Possibly tPe most cohe lex thinomplex phing on the planet o h ossibly tmp most cg on the tlanet ! ! ! ! ! ! ! ! ! Human brains can: Plan o I t a coordina o c movement and ovement and p n brains can: In additionn o ddition tingoordinating mperception, humaerception, human brains Be creative Be self aware Think Solve problems Manipulate and/or assist other human brains Self medicate Fall in love Etc. ! ! Brains without biology " Robots use electronic circuitry to connect sensation (and knowledge) to behavior, in a meaningful way ! ! Bra• nsBrains wtithout biology i withou biology " o e elect use c circuitr c to conno c sensa ion (and ( now edge) to Robots usRobots ronielectronic yircuitry tectonnect tsensation kand klnowledge) behavior, to behavior, in fa mway in a meaning ul eaningful way ! • How neurons work o Dendrites pick up chemical signals from neural transmitters o If enough signals are picked up the cell fires an electric charge o The charge travels down the axon to the presynaptic terminals (or buttons) that release neural transmitters into synaptic cleft o The neural transmitters are detected by dendrites at the synaptic cleft and the process begins again Some facts ! Neurons are binary (i.e. they have two states): they either fire or they don’t • Some facts o There are numerous different types of neurons but they are all the same at a certain level All are excited by neurotransmitters and this leads to firing a charge down the axon, which released neural transmitters o Neurons are binary (i.e. they have two states): they either fire or they don’t This is similar to computers, which are also binary o Human knowledge is not believed to be stored in individual neurons e.g. the grandmother neuron Instead it is believed to reside in the pattern of connections and activation between neurons o Speed of transmission down the axon ranges from approximately 1 mile an hour to 270 miles per hour This is much slower than a computer o There are estimated to be approximately 100 billion neurons and 100 trillion synapses this is much much more capacity than any computer o The power of the brain comes from massive computing power massive parallel processing o The brain stores information by Changing the electrical patterns • Fast Growing new connections and letting old ones die off Slow • Growing new neurons • Mainly in infants and children • Now known to occur somewhat in adults Biological complications o Electrical synapses smaller and faster, can directly stimulate using electrical charge o Dendrites may be able to boost or attenuate signals backpropagating action potentials may play a role o Glial cells Neurons and glia make up the two chief cell types of the central nervous system Glia outnumber neurons by as many as 10:1, some estimate 50:1 Traditionally glia cells have been viewed as a support mechanism for neurons Now known that glia can act and react to neural transmitters • o Quantum computing Roger Penrose has argued that the brain can compute things at the quantum level using particle states isolated in the microtubules of the neurons o Question These exist but are they used for information processing? Or do they just provide support? • The neural cognitive gap o We know a lot about our cognitive abilities and a lot about neurons, but… But we do not know how neurons function together to produce cognitive abilities such as memory attention and perception o Methods Dissecting brains • Good for finding the connections between areas Single cell recording • Not so usable on humans (requires implanting) • Limited to single cells Neural imaging • fMRI, EEG, CAT scan, etc. • shows relatively large areas associated with specific functions • Not good for looking at the workings of specific neural circuits • Assumes modularity Models • Build models using simulated neurons on a computer • See what kind of information processing they can do o Methods are (ideally) used in combination o Must also be guided by cognitive theory Knowing what areas are active during a task does not explain what the brain is doing To make sense of imaging data we need to know what the brain is doing during the imaging – the functions it is carrying out If we have a wrong view of the functions we will interpret the imaging data wrongly • Brain plasticity o if a part of the brain is destroyed (e.g., by a stoke) those functions can be taken on by other parts of the brain o this shows all of the information needed is not stored within the area different brain areas can do different things makes sense, they are all made of the same stuff – neurons they are not like different organs in the body o Examples of plasticity Deaf people • Have better o Peripheral vision o Motion detection • Because these are also processed in auditory cortex Blind people • Better at o Reading brail o Verbal memory • Because these are also processed in visual cortex • Also use it to process language o The brain adapts over time to normalize changes Drugs • at first a drug will have a strong effect but over time the brain will adapt to the drug • so you need the drug just to feel normal • if the drug is stopped then the brain needs time to adapt back to normal functioning Stress • chronic stress causes you to internally manufacture chemicals that were never meant to be used so much • this can also cause long lasting effects on the brain • sometimes drugs are given to try to get the brain into a more normal state • e.g., anti anxiety drugs Money • studies show that people who win the lottery are no happier a year later The brain adapts to training • if we do something a lot the brain assumes it's important and increases its ability to process along those lines ...
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This note was uploaded on 12/15/2010 for the course LING LING 1001 taught by Professor Bob during the Spring '10 term at Carleton CA.

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