title: Dynamic mechanisms underlying afterdischarge: a human subdural recording study.
abstract: OBJECTIVE
  No synoptic understanding exists of how and why afterdischarges (ADs) occur following electrical stimulation of the cerebral cortex. Based on human observations, we formulated a general mechanism for the emergence of ADs.
  
  
  METHODS
  We retrospectively analysed spectra of AD time-series and control segments of the resting electrocorticogram (ECoG) in 15 epilepsy patients who underwent cortical stimulation mapping. The observations led to the development of phenomenological models for AD emergence and morphology.
  
  
  RESULTS
  An analytical relationship exists between the spectrum of the baseline ECoG and the ensuing AD, characterised by 'condensation' of the main baseline spectral cluster, with variable inclusion of higher harmonics of the condensate.
  
  
  CONCLUSIONS
  ADs arise by synchronisation of pre-existing local field potentials, likely through temporary inactivation of inhibitory interneurons from repetitive stimulation-induced depolarization. The appearance of higher harmonics indicates that ADs are further modulated by recurrent feedback, likely from the entrained activity of single units.
  
  
  CONCLUSIONS
  For the first time, a putative mechanism is suggested for AD emergence following electrical stimulation of the cerebral cortex. Insight is also offered into several empirical observations regarding ADs, detailed in the main text. More generally, a novel conceptual synthesis emerges between the behaviour of electrically-excited cortex and the physics of nonlinearly coupled multi-oscillator systems.
authors.affiliation: Department of Neurology, University of Texas Health Science Center, Houston, TX, USA. Electronic address: Giridhar.P.Kalamangalam@uth.tmc.edu.
authors.forename: Giridhar P
authors.initials: GP
authors.lastname: Kalamangalam
authors.affiliation: Department of Neurosurgery, University of Texas Health Science Center, Houston, TX, USA.
authors.forename: Nitin
authors.initials: N
authors.lastname: Tandon
authors.affiliation: Department of Neurology, University of Texas Health Science Center, Houston, TX, USA.
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: Slater
mesh_terms: D000328:Adult; D000368:Aged; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000503:physiopathology; D004558:Electric Stimulation; D004569:Electroencephalography; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D016571:Neural Networks, Computer; D017711:Nonlinear Dynamics; D012189:Retrospective Studies; D012640:Seizures / Q000175:diagnosis / Q000503:physiopathology*; D013355:Subdural Space / Q000503:physiopathology
keywords: Cortical stimulation mapping; Electroencephalogram; Fourier analysis; Partial epilepsy; Weiner–Winfree–Kuramoto model