?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.title=Bicoherence+of+intracranial+EEG+in+sleep%2C+wakefulness+and+seizures&rft.creator=Bullock%2C+T.H.&rft.creator=Achimowicz%2C+J.Z.&rft.creator=Duckrow%2C+R.B.&rft.creator=Spencer%2C+S.S.&rft.creator=Iragui-Madoz%2C+V.J.&rft.subject=Biophysics&rft.subject=Brain+Imaging&rft.subject=Neuroanatomy&rft.subject=Neurolinguistics&rft.subject=Neural+Modelling&rft.subject=Neurology&rft.subject=Neurophysiology&rft.subject=Neurophysiology&rft.description=The+hypothesis+that+the+intracranial+EEG+has+local+structure+and+short-term+non-stationarity+is+tested+with+a+little-studied+measure+of+nonlinear+phase+coupling%2C+the+bicoherence+in+human+subdural+and+deep+temporal+lobe+probe+data+from+11+subjects+during+sleeping%2C+waking+and+seizure+states.+This+measure+of+cooperativity+estimates+the+proportion+of+energy+in+every+possible+pair+of+frequency+components%2C+F1%2C+F2+(from+1-50+Hz+in+this+study)%2C+that+satisfies+the+definition+of+quadratic+phase+coupling+(phase+of+component+at+F3+%2C+which+is+F1%2BF2%2C+equals+phase+of+F1+%2B+phase+of+F2).+Derived+from+the+bispectrum%2C+which+segregates+the+nonGaussian+energy%2C+auto-bicoherence+uses+the+frequency+components+in+one+channel%3B+cross-bicoherence+uses+one+channel+for+F1+and+F2+and+another+for+F3.+These+higher+order+spectra+are+used+in+physical+systems+for+detection+of+episodes+of+nonlinearity+and+transients%2C+for+pattern+recognition+and+robust+classification%2C+relatively+immune+to+Gaussian+components+and+low+signal+to+noise+ratios.+Bicoherence+is+found+not+to+be+a+fixed+character+of+the+EEG+but+quite+local+and+unstable%2C+in+agreement+with+the+hypothesis.+Bicoherence+can+be+quite+different+in+adjacent+segments+as+brief+as+1.6+s+as+well+as+adjacent+intracranial+electrodes+as+close+as+6.5+mm%2C+even+when+the+EEG+looks+similar.+It+can+rise+or+fall+steeply+within+millimeters.+It+is+virtually+absent+in+many+analysis+epochs+of+17s+duration.+Other+epochs+show+significant+bicoherence+with+diverse+form+and+distribution+over+the+bifrequency+plane.+Isolated+peaks%2C+periodic+peaks+or+rounded+mountain+ranges+are+either+widely+scattered+or+confined+to+one+or+a+few+parts+of+the+plane.+Bicoherence+is+generally+an+invisible+feature%3A+one+cannot+usually+recognize+the+responsible+form+of+nonlinearity+or+any+obvious+correlate+in+the+raw+EEG.+During+stage+II%2FIII+sleep+overall+mean+bicoherence+is+generally+higher+than+in+the+waking+state.+During+seizures+the+diverse+EEG+patterns+average+a+significant+elevation+in+bicoherence+but+have+a+wide+variance.+Maximum+bispectrum%2C+maximum+power+spectrum%2C+maximum+and+mean+bicoherence%2C+skewness+and+asymmetry+all+vary+independently+of+each+other.+Cross-bicoherence+is+often+intermediate+between+the+two+auto-bicoherence+spectra+but+commonly+resembles+one+of+the+two.+Of+the+known+factors+that+contribute+to+bicoherence%2C+transient+as+distinct+from+ongoing+wave+forms+can+be+more+important+in+our+data+sets.+This+measure+of+nonlinear+higher+moments+is+very+sensitive+to+weak+quadratic+phase+coupling%2C%3B+this+can+come+from+several+kinds+of+waveforms.+New+methods+are+needed+to+evaluate+their+respective+contributions.+Utility+of+this+descriptor+cannot+be+claimed+before+more+carefully+defined+and+repeatable+brain+states+are+studied.&rft.date=1997&rft.type=Journal+(Paginated)&rft.type=PeerReviewed&rft.format=text%2Fhtml&rft.identifier=http%3A%2F%2Fcogprints.org%2F122%2F1%2FEEG_BICO.htm&rft.identifier=++Bullock%2C+T.H.+and+Achimowicz%2C+J.Z.+and+Duckrow%2C+R.B.+and+Spencer%2C+S.S.+and+Iragui-Madoz%2C+V.J.++(1997)+Bicoherence+of+intracranial+EEG+in+sleep%2C+wakefulness+and+seizures.++%5BJournal+(Paginated)%5D+++++&rft.relation=http%3A%2F%2Fcogprints.org%2F122%2F