Are high-frequency (600 Hz) oscillations in human somatosensory evoked potentials due to phase-resetting phenomena?
OBJECTIVE
Median nerve somatosensory evoked potentials (SEP) contain a brief oscillatory wavelet burst at about 600 Hz (σ-burst) superimposed on the initial cortical component (N20). While invasive single-cell recordings suggested that this burst is generated by increased neuronal spiking activity in area 3b, recent non-invasive scalp recordings could not reveal concomitant single-trial added-activity, suggesting that the SEP burst might instead be generated by phase-reset of ongoing high-frequency EEG. Here, a statistical model and exemplary data are presented reconciling these seemingly contradictory results.


METHODS
A statistical model defined the conditions required to detect added-activity in a set of single-trial SEP. Its predictions were tested by analyzing human single-trial scalp SEP recorded with custom-made low-noise amplifiers.


RESULTS
The noise level in previous studies did not allow to detect single-trial added-activity in the period concomitant with the trial-averaged σ-burst. In contrast, optimized low-noise recordings do reveal added-activity in a set of single-trials.


CONCLUSIONS
The experimental noise level is the decisive factor determining the detectability of added-activity in single-trials. A low-noise experiment provided direct evidence that the SEP σ-burst is at least partly generated by added-activity matching earlier invasive single-cell recordings.


CONCLUSIONS
Quantitative criteria are provided for the feasibility of single-trial detectability of band-limited added-activity.
Neurophysics Group, Department of Neurology, Campus Benjamin Franklin, Charite-University Medicine Berlin, Berlin, Germany. gunnar.waterstraat@charite.de
Gunnar
G
Waterstraat
Bartosz
B
Telenczuk
Martin
M
Burghoff
Tommaso
T
Fedele
Hans J
HJ
Scheer
Gabriel
G
Curio
D000328:Adult; D004558:Electric Stimulation; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology*; D008875:Middle Aged; D013003:Somatosensory Cortex / Q000502:physiology*