High-frequency oscillations in somatosensory system

A Biomarker for Benign Adult Familial Myoclonus Epilepsy: High-Frequency Activities in Giant Somatosensory Evoked Potentials

BACKGROUND

Benign adult familial myoclonus epilepsy (BAFME) is one of the diseases that cause cortical myoclonus (CM) with giant somatosensory evoked potentials (SEPs). There are no useful diagnostic biomarkers differentiating BAFME from other CM diseases.

OBJECTIVE

To establish reliable biomarkers including high-frequency oscillations (HFOs) with giant SEPs for the diagnosis of BAFME.

METHODS

This retrospective case study included 49 consecutive CM patients (16 BAFME and 33 other CM patients) who exhibited giant P25 or N35 SEPs. SEPs were processed by a band-pass filter of 400-1000 Hz to analyze HFOs. Clinical and SEP findings were compared between (1) BAFME and other CM groups and (2) patients with presence and absence of P25-HFOs (HFOs superimposed on giant P25). The diagnostic power of each factor for BAFME was calculated.

RESULTS

All 16 BAFME patients showed SEP P25-HFOs with significantly higher occurrence (P < 0.0001) compared with that of other CM groups. The presence of P25-HFOs significantly correlated with a BAFME diagnosis (P < 0.0001) and high SEP P25 and N35 amplitudes (P = 0.01 and P < 0.0001, respectively). BAFME was reliably diagnosed using P25-HFOs with high sensitivity (100%), specificity (87.9%), positive predictive value (80%), and negative predictive value (100%), demonstrating its superiority as a diagnostic factor compared to other factors.

CONCLUSIONS

P25-HFOs with giant SEPs is a potential biomarker for BAFME diagnosis. P25-HFOs may reflect cortical hyperexcitability partly due to paroxysmal depolarizing shifts in epileptic neuronal activities and higher degrees of rhythmic tremulousness than those in ordinary CM. © 2021 International Parkinson and Movement Disorder Society.

Somatosensory High Frequency Oscillations reflect clinical fluctuations in migraine

OBJECTIVE

It has been demonstrated that the early part of 600 Hz High Frequency Oscillations (HFOs), probably generated in the terminal part of thalamo-cortical somatosensory radiations, are abnormally reduced between attacks in migraineurs. We aimed at verifying whether spontaneous clinical fluctuations in migraine are correlated to HFO changes.

METHODS

We recorded somatosensory evoked potentials in 28 migraine patients. Clinical fluctuations (number of attacks in the 6 months preceding and following the test) were correlated to the HFOs' amplitudes. Moreover, eight out of 28 patients underwent a longer follow-up, including HFO control and clinical observation during the 12 months following the baseline recording.

RESULTS

The amplitude of early presynaptic HFOs was significantly correlated to the clinical evolution, since spontaneous worsening was associated with reduced presynaptic HFOs, whereas spontaneous improvement was associated with enhanced presynaptic HFOs (correlation test, p<0.05). No correlation was found between the amplitude of postsynaptic HFOs and clinical fluctuations. Patients undergoing longer follow-up showed substantially unchanged HFOs, accordingly with their stable clinical condition.

CONCLUSIONS

HFOs' enhancement in spontaneously improved patients can reflect the increased activity of brainstem arousal related structures, which in turn increases the thalamo-cortical drive and the cortical lateral inhibition mediated by GABAergic interneurons.

SIGNIFICANCE

HFOs' recording could represent a useful tool in the functional assessment of migraine.

Somatosensory evoked potentials recorded from the human pedunculopontine nucleus region

The pedunculopontine nucleus region (PPNR) is an integral component of the midbrain locomotor region and has widespread connections with the cortex, thalamus, brain stem, cerebellum, spinal cord, and especially, the basal ganglia. No previous study examined the somatosensory connection of the PPNR in human. We recorded somatosensory evoked potentials (SEP) from median nerve stimulation through deep brain stimulation (DBS) electrodes implanted in the PPNR in 8 patients (6 with Parkinson's disease, 2 with progressive supranuclear palsy). Monopolar recordings from the PPNR contacts showed triphasic or biphasic potentials. The latency of the largest negative peak was between 16.8 and 18.7 milliseconds. Bipolar derivation revealed phase reversal with median nerve stimulation contralateral to the DBS electrode in 6 patients. There was no difference in SEP amplitude and latency between on and off medication states. We also studied the high frequency oscillations (HFOs) by filtering the signal between 500 and 2,500 Hz. The HFOs could be identified only from contralateral stimulation and had intraburst frequencies of 1061 ± 121 Hz, onset latencies of 13.8 ± 1.2 milliseconds, and burst durations of 7.3 ± 1.1 milliseconds. Among the 10 recordings with HFOs, only 1 had possible phase reversal in the bipolar derivation. Our results suggest that there are direct somatosensory inputs to the PPNR. The slow components and HFOs of the SEP have different origins.

Neuromagnetic correlates of developmental changes in endogenous high-frequency brain oscillations in children: a wavelet-based beamformer study

Recent studies have found that the brain generates very fast oscillations. The objective of the present study was to investigate the spectral, spatial and coherent features of high-frequency brain oscillations in the developing brain. Sixty healthy children and 20 healthy adults were studied using a 275-channel magnetoencephalography (MEG) system. MEG data were digitized at 12,000 Hz. The frequency characteristics of neuromagnetic signals in 0.5-2000 Hz were quantitatively determined with Morlet wavelet transform. The magnetic sources were volumetrically estimated with wavelet-based beamformer at 2.5 mm resolution. The neural networks of endogenous brain oscillations were analyzed with coherent imaging. Neuromagnetic activities in 8-12 Hz and 800-900 Hz were found to be the most reliable frequency bands in healthy children. The neuromagnetic signals were localized in the occipital, temporal and frontal cortices. The activities in the occipital and temporal cortices were strongly correlated in 8-12 Hz but not in 800-900 Hz. In comparison to adults, children had brain oscillations in intermingled frequency bands. Developmental changes in children were identified for both low- and high-frequency brain activities. The results of the present study suggest that the development of the brain is associated with spatial and coherent changes of endogenous brain activities in both low- and high-frequency ranges. Analysis of high-frequency neuromagnetic oscillation may provide novel insights into cerebral mechanisms of brain function. The noninvasive measurement of neuromagnetic brain oscillations in the developing brain may open a new window for analysis of brain function.

The effect of mobile phone electromagnetic fields on the alpha rhythm of human electroencephalogram

Mobile phones (MP) emit low-level electromagnetic fields that have been reported to affect neural function in humans; however, demonstrations of such effects have not been conclusive. The purpose of the present study was to test one of the strongest findings in the literature; that of increased "alpha" power in response to MP-type radiation. Healthy participants (N = 120) were tested using a double-blind counterbalanced crossover design, with each receiving a 30-min Active and a 30-min Sham Exposure 1 week apart, while electroencephalogram (EEG) data were recorded. Resting alpha power (8-12 Hz) was then derived as a function of time, for periods both during and following exposure. Non-parametric analyses were employed as data could not be normalized. Previous reports of an overall alpha power enhancement during the MP exposure were confirmed (relative to Sham), with this effect larger at ipsilateral than contralateral sites over posterior regions. No overall change to alpha power was observed following exposure cessation; however, there was less alpha power contralateral to the exposure source during this period (relative to ipsilateral). Employing a strong methodology, the current findings support previous research that has reported an effect of MP exposure on EEG alpha power.

Median nerve somatosensory evoked potentials and their high-frequency oscillations in amyotrophic lateral sclerosis

OBJECTIVE

To investigate sensory cortical changes in amyotrophic lateral sclerosis (ALS), we studied somatosensory evoked potentials (SEPs) and their high-frequency oscillation potentials.

METHODS

Subjects were 15 healthy volunteers and 26 ALS patients. Median nerve SEPs were recorded and several peaks of oscillations were obtained by digitally filtering raw SEPs. The patients were sorted into three groups according to the level of weakness of abductor pollicis brevis muscle (APB): mild, moderate and severe. The latencies and amplitudes of main and oscillation components of SEP were compared among normal subjects and the three patient groups.

RESULTS

The early cortical response was enlarged in the moderate weakness group, while it was attenuated in the severe weakness group. No differences were noted in the size ratios of oscillations to the main SEP component between the patients and normal subjects. The central sensory conduction time (CCT) and N20 duration were prolonged in spite of normal other latencies.

CONCLUSIONS

The median nerve SEP amplitude changes are associated with motor disturbances in ALS. The cortical potential enhancement of SEPs with moderate weakness in ALS may reflect some compensatory function of the sensory cortex for motor disturbances.

SIGNIFICANCE

The sensory cortical compensation for motor disturbances is shown in ALS, which must be important information for rehabilitation.