title: Non-invasive single-trial detection of variable population spike responses in human somatosensory evoked potentials.
abstract: OBJECTIVE
  Somatosensory evoked potentials (SEPs) around 600 Hz ('σ-bursts') are correlates of cortical population spikes. Recently, single-trial σ-bursts were detected in human scalp EEG using 29-channel low-noise recordings in an electromagnetically shielded room. To achieve clinical applicability, this study aimed to establish a protocol using only 8 EEG channels in an unshielded environment and to quantify the variability of σ-bursts.
  
  
  METHODS
  Median nerve SEPs were recorded in 10 healthy subjects using a custom-built low-noise EEG amplifier. A detection algorithm for single-trial σ-bursts was trained as combination of spatio-temporal filters and a non-linear classifier. The single-trial responses were probed for the presence of significant increases of amplitude and variability.
  
  
  RESULTS
  Single-trial σ-burst detection succeeded with Detection Rates and Positive Predictive Values above 80% in subjects with high SNR. A significant inter-trial variability in the amplitudes of early low-frequency SEPs and σ-bursts could be demonstrated.
  
  
  CONCLUSIONS
  Single-trial σ-bursts can be detected on scalp-EEG using only 8 EEG channels in an electromagnetically disturbed environment. The combination of dedicated hardware and detection algorithms allows quantifying and describing their variability.
  
  
  CONCLUSIONS
  The variability of population spikes in the human somatosensory cortex can be traced non-invasively in a clinical setting.
authors.affiliation: Neurophysics Group, Department of Neurology, Campus Benjamin Franklin, Charité - University Medicine Berlin, Hindenburgdamm 30, 12203 Berlin, Germany. Electronic address: gunnar.waterstraat@charite.de.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Waterstraat
authors.affiliation: Neurophysics Group, Department of Neurology, Campus Benjamin Franklin, Charité - University Medicine Berlin, Hindenburgdamm 30, 12203 Berlin, Germany; Medizinische Ingenieurswissenschaft, Universität zu Lübeck, Ratzeburger Allee 160, 23563 Lübeck, Germany.
authors.forename: Manuel
authors.initials: M
authors.lastname: Scheuermann
authors.affiliation: Neurophysics Group, Department of Neurology, Campus Benjamin Franklin, Charité - University Medicine Berlin, Hindenburgdamm 30, 12203 Berlin, Germany; Bernstein Center for Computational Neuroscience Berlin, Germany.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Curio
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D004558:Electric Stimulation / Q000379:methods; D004569:Electroencephalography / Q000379:methods*; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology; D008875:Middle Aged; D013003:Somatosensory Cortex / Q000502:physiology*; D055815:Young Adult
keywords: Evoked potentials; Excitability; High-frequency oscillations; Single-trial detection; Somatosensory system; Variability