?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.title=EEG+coherence+has+structure+in+the+millimeter+domain&rft.creator=Bullock%2C+T.H.&rft.creator=McClune%2C+M.&rft.creator=Achimowicz%2C+J.&rft.creator=V.J.%2C+Iragui-Madoz&rft.creator=R.B.%2C+Duckrow&rft.creator=S.S.%2C+Spencer&rft.subject=Brain+Imaging&rft.subject=Neural+Modelling&rft.subject=Neurology&rft.subject=Neurophysiology&rft.subject=Neurophysiology&rft.subject=Neuropsychology&rft.description=Subdural+recordings+from+8+patients+via+rows+of+eight+electrodes+with+either+5+or+10+mm+spacing+plus+depth+recordings+from+3+patients+with+rows+of+8-12+electrodes+either+6.5+or+9+mm+center-to-center+were+searched+for+signs+of+significant+local+differentiation+of+coherence+calculated+between+all+possible+pairs+of+loci.+EEG+samples+of+2-4+min+were+taken+during+four+states%3A+alertness%2C+stage+2-3+sleep%2C+light+surgical+anesthesia+permitting+the+patient+to+respond+to+questions+or+commands%2C+and+electrical+seizures.+Coherence+was+computed+for+all+frequencies+from+1-50+Hz+or+0.3-100+Hz+and+then+compared+for+6+or+7+narrower+bands+between+2+and+70+Hz.+In+both+the+subdural+surface+samples+and+those+from+temporal+lobe+depth+electrode+arrays+coherence+declines+with+distance+between+electrodes+of+the+pair%2C+on+the+average.+This+is+nearly+the+same+for+all+frequency+bands.+Whether+computed+for+5%2C+20+or+60+s+epochs%2C+coherence+pooled+across+all+pairs+of+a+given+separation%2C+in+a+given+subject%2C+differs+only+slightly%2C+in+the+direction+of+lower+coherence+for+longer+samples%2C+indicating+good+stationarity+of+the+samples+chosen.+For+middle+bands+like+8-13+and+13-20+Hz%2C+mean+coherence+typically+declines+most+steeply+in+the+first+10+mm%2C+from+values+indistinguishable+from+1.0+at+%3C0.5+mm+distance+to+0.5+at+5-10+mm+and+to+0.25+in+another+10-20+mm+in+the+subdural+surface+data.+Temporal+lobe+depth+estimates+decline+ca.+half+as+fast%3B+coherence+0.5+extends+for+9-20+mm+and+0.25+for+another+20-35+mm.+Low+frequency+bands+(1-5%2C+5-8+Hz)+usually+fall+slightly+more+slowly+than+high+frequency+bands+(20-35%2C+35-50+Hz)+but+the+difference+is+small+and+variance+large.+The+steepness+of+decline+with+distance+in+humans+is+significantly+but+only+slightly+smaller+than+that+we+reported+earlier+for+the+rabbit+and+rat%2C+averaging+%3C+one+half.+Local+coherence%2C+for+individual+pairs+of+loci%2C+shows+differentiation+in+the+millimeter+range%2C+i.e.+nearest+neighbor+pairs+may+be+locally+well+above+or+below+average+and+this+is+sustained+over+minutes.+Local+highs+and+lows+tend+to+be+similar+for+widely+different+frequency+bands.+Coherence+varies+quite+independently+of+power%2C+although+they+are+sometimes+correlated.+Regional+differentiation+is+statistically+significant+in+average+coherence+among+pairs+of+loci+on+temporal+vs+frontal+cortex+or+lateral+frontal+vs+subfrontal+strips+in+the+same+patient%2C+but+such+differences+are+usually+small.+We+could+not+test+how+consistent+they+are+over+hours+or+between+patients.+Differences+between+left+and+right+hemispheres%2C+whether+symmetrical+pairs+or+pooled+from+two+or+more+lobes+on+each+side%2C+can+be+quite+large%3B+in+our+patients+the+right+side+is+usually+higher%2C+especially+in+the+waking+state.+Brain+state+has+a+large+influence.+Slow+wave+sleep+usually+shows+slightly+more+coherence+at+each+distance%2C+in+all+bands%2C+compared+to+the+waking+EEG%2C+but+not+consistently.+Coherence+at+a+given+distance+or+its+rate+of+decline+with+distance+is+a+more+direct+measure+of+synchrony+than+naked-eye+%22synchronization%2C%22+which+is+dominated+by+the+power+spectrum.+Among+the+range+of+EEG+states+classified+as+seizures%2C+coherence+varies+widely+but+averages+higher+by+0.05-0.2+than+in+pre-ictal+states%2C+usually+in+all+frequencies+when+computed+over+the+whole+seizure+but+much+more+in+the+higher+bands+during+the+height+of+the+electrical+paroxysm.+The+findings+point+to+still+finer+structure+and+more+variance+with+closer+spacing+of+electrodes.+They+could+not+predict+the+known+large+scale+coherence+between+scalp+electrodes%2C+but+are+not+in+conflict+with+them.+Scalp+recording+blurs+the+finer+spatial+structure%2C+but+reveals+macrostructure+missed+by+subdural+and+depth+recording+with+limited+numbers+of+channels.+The+strong+tendency+for+correlated+fluctuations+across+frequency+bands+is+contrary+to+expectation+from+the+common+model+of+independent+oscillators.&rft.date=1995&rft.type=Journal+(Paginated)&rft.type=PeerReviewed&rft.format=text%2Fhtml&rft.identifier=http%3A%2F%2Fcogprints.org%2F133%2F1%2FEEG_coh_struc.htm&rft.identifier=++Bullock%2C+T.H.+and+McClune%2C+M.+and+Achimowicz%2C+J.+and+V.J.%2C+Iragui-Madoz+and+R.B.%2C+Duckrow+and+S.S.%2C+Spencer++(1995)+EEG+coherence+has+structure+in+the+millimeter+domain.++%5BJournal+(Paginated)%5D+++++&rft.relation=http%3A%2F%2Fcogprints.org%2F133%2F