Non-invasive single-trial detection of variable population spike responses in human somatosensory evoked potentials

• Low-noise 8-channel SEP permit single-trial detection of cortical population spikes even in an electromagnetically noisy clinical environment.
• Single-trial amplitudes of low-frequency SEPs and σ-bursts are shown to vary significantly.
• Thus, the variability of population spikes in the human somatosensory cortex can be traced non-invasively in a clinical setting.

ObjectiveSomatosensory 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.MethodsMedian 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.ResultsSingle-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.ConclusionsSingle-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.SignificanceThe variability of population spikes in the human somatosensory cortex can be traced non-invasively in a clinical setting.