Article

The effects of stimulus rates on high frequency oscillations of median nerve somatosensory-evoked potentials - Direct recording study from the human cerebral cortex

Department of Neurosurgery, School of Medicine, University of Occupational and Environmental Health, Iseigaoka 1-1, Yahata Nishi-ku, Kitakyushu City 807-8555, Japan.
Clinical Neurophysiology (Impact Factor: 3.1). 12/2002; 113(11):1794-7. DOI: 10.1016/S1388-2457(02)00291-2
Source: PubMed

ABSTRACT

To study the effects of different stimulus rates on high-frequency oscillations (HFOs) of somatosensory-evoked potentials (SEPs), we recorded median nerve SEPs directly from the human cerebral cortex.
SEPs were recorded from subdural electrodes in 5 patients with intractable epilepsy, under the conditions of low (3.3Hz) and high (12.3Hz) stimulus rates.
Increased stimulus rates to the median nerve from 3.3 to 12.3Hz showed a pronounced amplitude reduction of HFOs when compared with the primary N20-P20, area 3b, and P25, area 1, responses.
HFOs were more sensitive to a high stimulus rate than the primary cortical responses, suggesting that the post-synaptic intracortical activities may greatly contribute to the HFO generation.

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    • "In this context, the finding of a robust HFO at 12.7 Hz stimulation rate is an interesting result in itself. In comparison to (Urasaki et al., 2002), we used a much higher number of averages (10000 vs. 1000), which improved the SNR by a factor of 3. This may explain why we obtained a robust HFO even at high stimulation rate. "
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    ABSTRACT: Objective The somatosensory evoked potential (SEP) elicited by median nerve stimulation consists of the N20 peak together with the concurrent high frequency oscillation (HFO, > 500 Hz). We describe the conditions for HFO detection in ECoG and scalp EEG in intraoperative recordings. Methods During neurosurgical interventions in six patients under propofol anesthesia, the SEP was recorded from subdural electrode strips (15 recordings) and from scalp electrodes (10/15 recordings). We quantified the spatial attenuation of the Signal-to-Noise Ratio (SNR) of N20 and HFO along the contacts of the electrode strip. We then compared the SNR of ECoG and simultaneous scalp EEG in a biophysical framework. Results HFO detection under propofol anesthesia was demonstrated. Visual inspection of strip cortical recordings revealed phase reversal for N20 in 14/15 recordings and for HFO in 10/15 recordings. N20 had higher maximal SNR (median 33.5 dB) than HFO (median 23 dB). The SNR of N20 attenuated with a larger spatial extent (median 7.2 dB/cm) than the SNR of HFO (median 12.3 dB/cm). We found significant correlations between the maximum SNR (rho = 0.58, p = 0.025) and the spatial attenuation (rho = 0.86, p < 0.001) of N20 and HFO. In 3/10 recordings we found HFO in scalp EEG. Based on the spatial attenuation and SNR in the ECoG, we estimated the scalp EEG amplitude ratio N20/HFO and found significant correlation with recorded values (rho = 0.65, p = 0.049). Conclusions We proved possible the intraoperative SEP HFO detection under propofol anesthesia. The spatial attenuation along ECoG contacts represents a good estimator of the area contributing to scalp EEG. The SNR and the spatial attenuation in ECoG recordings provide further insights for the prediction of HFO detectability in scalp EEG. The results obtained in this context may not be limited to SEP HFO, but could be generalized to biological signatures lying in the same SNR and frequency range.
    Full-text · Article · Dec 2015 · Clinical neuroimaging
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    ABSTRACT: We investigate a communication model made of an outer code interleaved with a space-time trellis coded modulation (ST-TCM). Such a scheme is very relevant for highly frequency selective and time-varying channels using turbo-detection at the receiver side, but inherently suffers from a low coding rate. One possible solution to alleviate this impairment (i.e., to increase spectral efficiency) is to use parallel (or multilayered) transmission as done in recent approaches (BLAST). However, parallel transmission and highly frequency selective channels involve tremendous complexity at the receiver side. We propose a low complexity turbo-detector based on reduced-state trellis search and generalized per survivor processing that proves to be very efficient in this resulting multiple-input multiple-output (MIMO) ISI channel context
    No preview · Conference Paper · Feb 2001
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    ABSTRACT: To determine whether patients with cervical dystonia have electrophysiological signs of disinhibition in the somatosensory cortex by recording high-frequency oscillations (HFOs) in somatosensory evoked potentials (SEPs). HFOs were recorded in 13 patients and 10 age-matched control subjects, and the data were analyzed statistically by paired comparison and by Pearson's correlation. In patients with cervical dystonia, the early part of HFOs showed a significant decrease in amplitude, and the amplitude ratios of both early and late parts of HFOs/N20 potential were also significantly decreased. The amplitudes of HFOs and N20 potential were linearly correlated in the control subjects but not in dystonia patients. Patients with cervical dystonia may suffer from a disturbance of inhibition in the sensory cortex. This disturbance is reflected by decreased HFO amplitude, representing decreased activities of inhibitory interneurons in area 3b.
    No preview · Article · Aug 2004 · Clinical Neurophysiology
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