?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.title=Temporal+fluctuations+in+coherence+of+brain+waves&rft.creator=Bullock%2C+T.H.&rft.creator=McClune%2C+M.C.&rft.creator=Achimowicz%2C+J.Z.&rft.creator=Iragui-Madoz%2C+V.J.&rft.creator=Duckrow%2C+R.B.&rft.creator=Spencer%2C+S.S.&rft.subject=Brain+Imaging&rft.subject=Brain+Imaging&rft.subject=Computational+Neuroscience&rft.subject=Neural+Modelling&rft.subject=Neurology&rft.description=As+a+measure+of+dynamical+structure%2C+short+term+fluctuations+of+coherencebetween+0.3+and+100+Hz+in+the+electroencephalogram+(EEG)+of+humans+were+studied+from+recordings+made+by+chronic+subdural+macroelectrodes+5-10+mm+apart%2C+on+temporal%2C+frontal+and+parietal+lobes%2C+and+from+intracranial+probes+deep+in+the+temporal+lobe%2C+including+the+hippocampus%2C+during+sleep%2C+alert+and+seizure+states.+The+time+series+of+coherence+between+adjacent+sites+calculated+every+second+or+less+often+varies+widely+in+stability+over+time%3B+sometimes+it+is+stable+for+half+a+minute+or+more.+Within+two+minute+samples%2C+coherence+commonly+fluctuates+by+a+factor+up+to+2+or+3%2C+in+all+bands%2C+within+the+time+scale+of+seconds+to+tens+of+seconds.+The+power+spectrum+of+the+time+series+of+these+fluctuations+is+broad%2C+extending+to+0.02+Hz+or+slower%2C+and+is+weighted+toward+the+slower+frequencies%3B+little+power+is+faster+than+0.5+Hz.+Some+records+show+conspicuous+swings+with+a+preferred+duration+of+5-15+s%2C+either+irregularly+or+quasi-rhythmically+with+a+broad+peak+around+0.1+Hz.+Periodicity+is+not+statistically+significant+in+most+records.+We+have+not+found+a+consistent+difference+between+lobes+of+the+brain%2C+subdural+and+depth+electrodes+or+sleeping+and+waking+states%2C+in+our+sampling.+Seizures+generally+raise+the+mean+coherence+in+all+frequencies+and+may+reduce+the+fluctuations+by+a+ceiling+effect.+The+coherence+time+series+of+different+bands+is+positively+correlated+(0.45+overall)%3B+significant+non-independence+extends+for+at+least+two+octaves.+Coherence+fluctuations+are+quite+local%3B+the+time+series+of+adjacent+electrodes+is+correlated+with+that+of+the+nearest+neighbor+pairs+(10+mm)+to+a+coefficient+averaging+ca.+0.4%2C+falling+to+ca.+0.2+for+neighbors-but-one+(20+mm)+and+to+%3C+0.1+for+neighbors-but-two+(30+mm).+The+evidence+indicates+fine+structure+in+time+and+space%2C+a+dynamic+and+local+determination+of+this+measure+of+cooperativity.+Widely+separated+frequencies+tending+to+fluctuate+together+exclude+independent+oscillators+as+the+general+or+usual+basis+of+the+EEG%2C+although+a+few+rhythms+are+well+known+under+special+conditions.+Broadband+events+may+be+the+more+usual+generators.+Loci+only+a+few+mm+apart+can+fluctuate+widely+in+seconds%2C+either+in+parallel+or+independently.+Scalp+EEG+coherence+cannot+be+predicted+from+subdural+or+deep+recordings%2C+or+vice+versa+and+intracortical+microelectrodes+show+still+greater+coherence+fluctuation+in+space+and+time+1.+Widely+used+computations+of+chaos+and+dimensionality%2C+made+upon+data+from+scalp+or+even+subdural+or+depth+electrodes%2C+even+when+reproducible+in+successive+samples%2C+cannot+be+considered+representative+of+the+brain+or+the+given+structure+or+brain+state+but+only+of+the+scale+or+view+(receptive+field)+of+the+electrodes+used.+Relevant+to+the+evolution+of+more+complex+brains%2C+which+is+an+outstanding+fact+of+animal+evolution%2C+we+believe+measures+of+cooperativity+are+likely+to+be+among+the+dynamic+features+by+which+major+evolutionary+grades+of+brains+differ.+In+spite+of+a+large+literature+on+the+electroencephalogram%2C+we+have+an+extremely+limited+picture+of+the+structure+of+activity+in+the+brain+on+the+scales+of+millimeters+and+seconds.+In+spite+of+a+prevailing+view+that+the+principal+generators+of+the+compound+field+potentials+in+the+brain+are+microscopic%2C+cellular+or+subcellular+and+chiefly+membrane+potentials%2C+our+extant+data+base+is+mainly+scalp+recordings+on+humans%2C+usually+40+mm+apart%2C+each+conservatively+estimated+to+take+the+vector+sum+of+activity+in+ca.+15+million+cells%2C+assuming+a+volume+1.5+mm+deep+x+10+x+10+mm+tangentially+at+50%2C000+neurons+per+cubic+millimeter+and+an+equal+number+of+glia.+In+spite+of+an+extensive+knowledge+of+cellular+interaction+by+synaptic+mechanisms%2C+our+quantitative+understanding+of+the+amount+of+interaction+by+this+route+versus+electrotonic+or+chemical+field+effects+is+almost+nil.+Under+such+circumstances%2C+we+consider+quite+vulnerable+such+concepts+as+synchronization%2C+resonance%2C+rhythmicity+and+independence+of+frequency+components+of+the+EEG+-+each+an+inference%2C+but+seldom+measured.+The+present+report+is+one+of+a+series+aiming+at+some+insight+into+the+fine+structure+in+space+and+time+of+the+dynamical+signs+provided+in+the+compound+field+potentials%2C+as+recorded+directly+on+or+in+the+brain+1%2C+2%2C+3%2C+4%2C+5%2C+6%2C+7%2C+8%2C+9.+The+main+goal+is+to+test+the+hypothesis+that+one+measure+of+cooperativity+at+each+frequency%2C+namely+coherence%2C+varies+in+time+on+the+scale+of+seconds+or+fractions+of+a+second%2C+with+evidence+of+more+than+stochastic+structure+and+that+the+fluctuation+is+different+for+closely+spaced+loci.+We+will+show+in+addition+that+a+wide+range+of+frequency+components+of+the+EEG+tend+to+covary+in+coherence%2C+contrary+to+the+usual+assumption+of+independent+oscillators.&rft.date=1995&rft.type=Journal+(Paginated)&rft.type=PeerReviewed&rft.format=text%2Fhtml&rft.identifier=http%3A%2F%2Fcogprints.org%2F111%2F1%2FTemp_fluc_coherence.htm&rft.identifier=++Bullock%2C+T.H.+and+McClune%2C+M.C.+and+Achimowicz%2C+J.Z.+and+Iragui-Madoz%2C+V.J.+and+Duckrow%2C+R.B.+and+Spencer%2C+S.S.++(1995)+Temporal+fluctuations+in+coherence+of+brain+waves.++%5BJournal+(Paginated)%5D+++++&rft.relation=http%3A%2F%2Fcogprints.org%2F111%2F