title: An investigation of EEG dynamics in an animal model of temporal lobe epilepsy using the maximum Lyapunov exponent.
abstract: Analysis of intracranial electroencephalographic (iEEG) recordings in patients with temporal lobe epilepsy (TLE) has revealed characteristic dynamical features that distinguish the interictal, ictal, and postictal states and inter-state transitions. Experimental investigations into the mechanisms underlying these observations require the use of an animal model. A rat TLE model was used to test for differences in iEEG dynamics between well-defined states and to test specific hypotheses: 1) the short-term maximum Lyapunov exponent (STL(max)), a measure of signal order, is lowest and closest in value among cortical sites during the ictal state, and highest and most divergent during the postictal state; 2) STL(max) values estimated from the stimulated hippocampus are the lowest among all cortical sites; and 3) the transition from the interictal to ictal state is associated with a convergence in STL(max) values among cortical sites. iEEGs were recorded from bilateral frontal cortices and hippocampi. STL(max) and T-index (a measure of convergence/divergence of STL(max) between recorded brain areas) were compared among the four different periods. Statistical tests (ANOVA and multiple comparisons) revealed that ictal STL(max) was lower (p<0.05) than other periods, STL(max) values corresponding to the stimulated hippocampus were lower than those estimated from other cortical regions, and T-index values were highest during the postictal period and lowest during the ictal period. Also, the T-index values corresponding to the preictal period were lower than those during the interictal period (p<0.05). These results indicate that a rat TLE model demonstrates several important dynamical signal characteristics similar to those found in human TLE and support future use of the model to study epileptic state transitions.
authors.affiliation: Department of Neurology, Allegheny General Hospital, Center for Neuroscience Research, Allegheny-Singer Research Intitute, Pittsburgh, PA, USA.
authors.forename: Sandeep P
authors.initials: SP
authors.lastname: Nair
authors.forename: Deng-Shan
authors.initials: DS
authors.lastname: Shiau
authors.forename: Jose C
authors.initials: JC
authors.lastname: Principe
authors.forename: Leonidas D
authors.initials: LD
authors.lastname: Iasemidis
authors.forename: Panos M
authors.initials: PM
authors.lastname: Pardalos
authors.forename: Wendy M
authors.initials: WM
authors.lastname: Norman
authors.forename: Paul R
authors.initials: PR
authors.lastname: Carney
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Kelly
authors.forename: J Chris
authors.initials: JC
authors.lastname: Sackellares
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000465:Algorithms; D000818:Animals; D003627:Data Interpretation, Statistical; D004195:Disease Models, Animal; D004558:Electric Stimulation; D004569:Electroencephalography / Q000379:methods*; D004833:Epilepsy, Temporal Lobe / Q000175:diagnosis* / Q000503:physiopathology*; D005071:Evoked Potentials / Q000502:physiology*; D006624:Hippocampus / Q000503:physiopathology; D007696:Kindling, Neurologic / Q000502:physiology; D008297:Male; D008959:Models, Neurological; D009474:Neurons / Q000502:physiology; D017711:Nonlinear Dynamics; D051381:Rats; D017207:Rats, Sprague-Dawley; D012815:Signal Processing, Computer-Assisted; D013226:Status Epilepticus / Q000503:physiopathology; D013702:Temporal Lobe / Q000503:physiopathology*