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. © 2010 Movement Disorder Society.     

Somatosensory evoked high frequency oscillations recorded from subdural electrodes

OBJECTIVES: To examine high frequency oscillations (HFOs) of somatosensory evoked potentials (SEPs) recorded directly from subdural electrodes to investigate the relationship between the primary somatosensory cortex and HFOs. METHODS: SEPs were recorded directly from subdural electrodes previously implanted in 3 patients for clinical evaluation prior to surgical treatment of intractable epilepsy. RESULTS: The primary sensory cortex (area 3b) was proposed as the source of somatosensory HFOs, because the distribution of HFOs recorded from the subdural electrodes agreed with the distribution of the N20-P20 components of the somatosensory evoked potential. The somatosensory HFOs showed a strictly somatotopic source arrangement. There was a polarity inversion of the prophase component and also the N20-P20 component of HFOs across the central sulcus. However, the phase was synchronized in the latter part of the HFOs. CONCLUSIONS: We propose that the origins of the early and latter parts of HFOs are different, and that there was a clear somatotopy.     

Intraoperative subdural low-noise EEG recording of the high frequency oscillation in the somatosensory evoked potential

Objective

The detectability of high frequency oscillations (HFO, >200 Hz) in the intraoperative ECoG is restricted by their low signal-to-noise ratio (SNR). Using the somatosensory evoked HFO, we quantify how HFO detectability can benefit from a custom-made low-noise amplifier (LNA).

Effects of the noncompetitive AMPA receptor antagonist perampanel on thalamo-cortical excitability: A study of high-frequency oscillations in somatosensory evoked potentials

ObjectiveWe designed a longitudinal cohort study on People with Epilepsy (PwE) with the aim of assessing the effect of Perampanel (PER) on cortico-subcortical networks, as measured by high-frequency oscillations of somatosensory evoked potentials (SEP-HFOs). SEP-HFOs measure the excitability of both thalamo-cortical projections (early HFOs) and intracortical GABAergic synapses (late HFOs), thus they could be used to study the anti-glutamatergic action of PER, a selective antagonist of the AMPA receptor.Methods15 PwE eligible for PER add-on therapy, were enrolled prospectively. Subjects underwent SEPs recording from the dominant hand at two times: PwE_T0 (baseline, before PER titration) and PwE_T1 (therapeutic dose of 4 mg). HFOs were obtained by filtering N20 scalp response in the 400–800 Hz range. Patients were compared with a normative population of 15 healthy controls (HC) matched for age and sex.ResultsWe found a significant reduction of Total HFOs and mostly early HFOs area between PwE_T0 and PwE_T1 (p = 0.05 and p = 0.045 respectively) and between HC and PwE_T1 (p = 0.01). Furthermore, we found a significant reduction of P24/N24 Amplitude between PwE_T0 and HC and between PwE_T0 and PwE_T1 (p = 0.006 and p = 0.032, respectively).ConclusionsIntroduction of PER as add-on therapy reduced the area of total HFOs, acting mainly on the early burst, related to thalamo-cortical pathways. Furthermore P24/N24 amplitude, which seems to reflect a form of cortico-subcortical integration, resulted increased in PwE at T0 and normalized at T1.SignificanceOur findings suggest that PER acts on cortico-subcortical excitability. This could explain the broad spectrum of PER and its success in forms of epilepsy characterized by thalamo-cortical hyperexcitability.     

Differential influence of posture and intentional movement on human somatosensory evoked potentials evoked by different stimuli

Somatosensory evoked potentials (SEP) recorded from humans were elicited by a cutaneous shock to the index finger or with a ramp displacement of the finger that stretched the first dorsal interosseous muscle. A somatosensory stimulus was presented while a subject maintained a steady posture of the metacarpophalangeal joint or during a rapid voluntary abduction of the index finger. Both activities were performed against a constant opposing load of 0.15 Nm or without a load. SEPs were recorded over the postcentral arm area, together with the electromyogram of the first dorsal interosseous muscle. The major components of the SEPs were P56, N130, P174, N232 and P294. The amplitudes of all components were diminshed substantially during active movement. A constant load opposing postural fixation or active movement did not influence the SEP amplitude. The amplitude of the P56 component was differentially affected by the shock or ramp stimuli. The findings demonstrate that active movement gates sensory input, while sustained tonic muscular activity with an opposing constant load does not, and that different somesthetic inputs may be processed differently during movement.     

Somatosensory evoked potentials and high frequency oscillations are differently modulated by theta burst stimulation over primary somatosensory cortex in humans

Objective

The effects of theta burst stimulation (TBS) have been extensively investigated in primary motor cortex, where it leads to long-lasting LTP/LTD-like effects on synaptic plasticity. This study aimed to extend these observations to sensory cortex.

Methods

Fourteen healthy subjects participated in the study. Conditioning 600-pulse intermittent TBS (iTBS) and continuous TBS (cTBS) were delivered to left somatosensory cortex (S1) with an intensity of 80% active motor threshold. Somatosensory evoked potentials (SEPs) were evoked by median nerve electrical stimulation at right wrist. High frequency oscillations (HFOs) were obtained by digital filtering of original SEPs and divided into early and late subcomponents, relative to N20_peak latency.

Results

Repeated-measures ANOVA showed that iTBS facilitated N20_onset–N20_peak at 15 min and N20_peak–P25 at 15 and 30 min after conditioning, whereas cTBS did not. iTBS left the early and late HFOs unchanged. Conversely, cTBS facilitated the early HFOs, whereas it inhibited the late HFOs at 15 min after conditioning.

Conclusions

S1-iTBS facilitated SEPs without changes in HFOs whereas cTBS modulated early and late HFOs without changes in SEPs.

Significance

S1-TBS produces lasting changes in the excitability of intracortical circuits generating SEPs and HFOs differentially through mechanisms of LTP/LTD-like synaptic plasticity.     

The effects of antiepileptic drugs on high-frequency oscillations in somatosensory evoked potentials

ObjectivesHigh frequency oscillations (HFOs) of Somatosensory evoked potentials (SEPs) reflect the activity of thalamo-cortical and cortical neurons from the sensory pathway. Antiepileptic-drugs (AEDs) reduce seizures acting on the balance between excitation and inhibition. We aimed to study the effect of AED mono and polytherapy on SEP-HFO’s components.MethodsTwenty-five patients with focal epilepsy were enrolled for the purpose of this study. Patients were divided in 3 groups according to the number of AEDs (1, 2 or 3 AEDs). Patients in group 1 underwent SEP-HFOs recording in drug naïve condition and at 1 month after AED titration. HFOs were compared in duration, amplitude and latency among the three groups.ResultsThe amplitude and duration of late HFOs of the affected hemisphere (AH) are different between groups and inversely correlated with the number of AEDs. In naïve patients monotherapy reverts the asymmetry in totHFOs (total HFOs) duration.ConclusionOur results demonstrate that SEP-HFOs are sensitive to the action of AEDs on cortical excitability. This effect seems to affect mainly the cortical component of HFOs in the AH and it is related to the number of AEDs taken.SignificanceSEP-HFOs might be a viable tool to probe cortical excitability changes induced by AEDs.     

听觉诱发电位及体感诱发电位在颅脑外伤致昏迷患者的应用

严重颅脑损伤昏迷患者脑功能的监测是判断预后和指导治疗的重要手段。听觉诱发电位(BAEP)及体感诱发电位(SSEP)因其方便、无创并能连续实时监测昏迷患者相关神经传导通路电生理的变化,间接反映脑干上行激活系统、大脑皮层结构与功能的完整性,越来越成为临床对严重颅脑损伤昏迷患者预测预后和指导治疗的重要手段。本文就近年来相关研究进行综述,旨在指导临床实践。     

The effect of deep brain stimulation on the frontal N30 component of somatosensory evoked potentials in advanced Parkinson's disease patients.

OBJECTIVES: In the present study we investigated whether in advanced Parkinson's disease (PD) patients the frontal component of short somatosensory evoked potentials (SEPs) to median nerve stimulation may be modified by basal ganglia deep brain stimulation (DBS). METHODS: We recorded the SEPs in 6 PD patients undergoing bilateral functional neurosurgery in the internal globus pallidus (GPi) (4 patients) and in the nucleus subthalamicus (STN) (two patients) during ineffective and effective bilateral BDS. Pre-operatively, the SEPs were also recorded in off therapy and during apomorphine infusion. RESULTS: From the evaluation of the latency and the amplitude characteristics of the major parietal (N20 and P25) and frontal (N30) components, we observed that whereas the parietal waves did not vary in any condition, the N30 potential showed a remarkable amplitude increase during apomorphine as well as during effective bilateral GPi or STN DBS. Furthermore, after the stimulators were turned off we noticed that the N30 amplitude potential progressively faded almost in parallel with the attenuation of DBS clinical effects. CONCLUSIONS: Our results lead to the conclusion that the bilateral DBS of both GPi and STN is really effective in producing a selective increase of frontal N30 amplitude probably improving the supplementary motor area functional activity, but these results do not clarify whether this amelioration is due to a central or a 'long loop' mechanism.     

Differential gating of slow postsynaptic and high-frequency spike-like components in human somatosensory evoked potentials under isometric motor interference

Human cortical somatosensory evoked potentials (SEP) can be modified by concomitant motor tasks ('gating'), through peripheral occlusion and/or central mechanisms. The present study aimed (1) at refining earlier results concerning motor-gating of the primary cortical EPSP-related N20 response after electric median nerve stimulation, and (2) at providing first data on motor-gating of the 600 Hz SEP wavelet burst which occurs superimposed onto N20 and primarily reflects repetitive cerebral population spikes. In 12 healthy subjects median nerve SEP were elicited, using electrical stimuli with intensities below, at and above motor threshold, under either rest or an isometric fist clenching task. Amplitude and latency modifications were analysed for the peripheral compound action potential (CAP), low-frequency SEP components (N20, P25, N35 and P70) and the high-frequency burst. While the peripheral CAP remained unchanged, isometric motor innervation significantly attenuated N20, P25 and P70 amplitudes and shortened peak latencies progressively for all components after N20. In contrast, the high-frequency 600 Hz burst was modulated neither in amplitude nor in latency. Regular amplitude recruitment occurred for all components independent from the motor task, excluding channel saturation as an explanation for gating. We suggest that SEP gating under isometric motor innervation is a central process which selectively operates on specific SEP components and could partly reflect an "efference copy" mechanism.     

Changes in somatosensory evoked responses by repetition of the median nerve stimulation

OBJECTIVE: We investigate the synaptic factor for the recovery function of evoked responses using a repetitive stimulation technique. METHODS: Somatosensory evoked cortical magnetic field (SEF) was recorded following stimulation of the median nerve using single to 6-train stimulation in 8 healthy subjects. The SEF responses after each stimulus in the train stimulation were extracted by subtraction of the waveforms. RESULTS: An attenuation of the SEF components was recognized after the second of the stimuli, but there was no significant attenuation with the third or later stimulations. The root mean square (RMS) of the 1M (peak latency at 20 ms after stimulation) and 4M (70 ms) components were smaller than that of the single stimulation during the train stimulation, while the 2M (30 ms) and 3M (45 ms) components were not attenuated, but the 3M was facilitated at the fourth to sixth stimulation. CONCLUSION: The synaptic factor was not responsible for the attenuation of the SEF components during repetitive stimulation in healthy subjects. The SEF change disclosed a functional difference among the SEF components during the train stimulation, especially among the later components.     

Bulbocavernosus reflex latencies and somatosensory evoked potentials after pudendal nerve stimulation in the diagnosis of impotence

Summary The bulbocavernosus reflex (BCR) was examined in 39 normal potent men and in 252 patients with impaired potency of varying aetiology. For BCR evaluation minimum, maximum and mean latencies, the temporal dispersion in ten successive responses, together with minimum and maximum side differences from simultaneous recordings of the left and right bulbocavernosus muscles were determined. Pathological findings were deteced in 125 patients. Somatosensory evoked potentials (SSEPs) recorded from the scalp after stimulation of the penile dorsal nerves and the terminal branches of the pudendal nerve were investigated in 30 controls and in 246 patients. An abnormal SSEP was found in 63 patients.     

The subcortical generated somatosensory evoked potentials in non-cephalic,cephalic, and anterior neck referenced recordings in a patient with a cervico-medullary lesion: a clue to the identification of the P14/N14 and N13 generators

Summary Median nerve somatosensory evoked potentials (SEPs) were studied in a patient before and after the development of a cervico-medullary lesion. The first examination demonstrated normal subcortical generated potentials N13 and N14. The second examination, following a subarachnoid haemorrhage at the cervico-medullary junction, displayed a delayed and reduced amplitude P14/N14 peak on both sides. P14/N14 showed the same latency in all montages, using noncephalic, cephalic and anterior neck references. The N13 component was not significantly changed in latency compared with the first examination. The latencies of the N13 peak were variable in the different montages. They increased from the lower (C7) to the upper (C2) neck, whereas the latency of the N13 onset was identical in all montages. This alteration might be caused by a delayed near-field activity at C2 overlapping the N13 component. These results fit the hypothesis of two major generators responsible for subcortical SEPs; a near-field N13 component at the level of the lower neck and a far-field P14 component arising from the level of the cervico-medullary junction. An additional minor near-field activity generated by the cuneate nucleus is suspected.     

Subthalamic somatosensory evoked potentials in Parkinson's disease.

Deep brain stimulation (DBS) of subthalamic nucleus (STN) is an effective treatment for advanced Parkinson's disease. It also provides an opportunity to record neural activity from the human basal ganglia. In this study, to investigate the involvement of the human STN in sensory functions, we recorded somatosensory evoked potentials (SEPs) elicited by contralateral median-nerve stimulation, from STN electrodes implanted for DBS in patients with Parkinson's disease. We suggest that the STN N18 component of SEPs in Parkinson's disease is a mainly local field potential elicited by muscle afferent input to the nucleus.     

The effects of focal epileptic activity on the somatosensory evoked potentials in the rat

Summary The cortical somatosensory evoked potential (SEP) of the rat, evoked by contralateral forepaw stimulation, consisted of early (P 1 and N 1) and late components (P 2 and N 2). Microelectrode recording yielded evoked unitary responses of short latencies in the range of the early components and responses of longer latencies in the range of P 2. During the development of focal epilepsy after topical application of penicillin, the late components of SEP were enhanced and the enhanced late negativity corresponded to a surface negative cortical spike. The prominent enlargement of later components was associated with prolonged, often recurrent discharges of longer latency unitary responses and with enlarged local field potentials. Early components of SEP remained relatively unaffected and so did unitary responses with short latencies.Epileptic spike-conditioned SEPs in the cuneate nucleus, thalamic sensory relay nucleus and sensory cortex were depressed from 100 ms (cuneate nucleus) to about 300 ms (thalamus and cortex) subsequent to spike discharge. Transmission in the cuneate nucleus was least affected. Thalamic and cortical early components of SEP had similar time courses of recovery, which differed markedly from that of cortical late components. Our findings suggest that two different neuronal activities generate different components of SEP and are differentially involved in the epileptic activities, which results in the different amplitude recovery following spontaneous epileptic spike discharges.This work was supported by the Deutsche Forschungsgemeinschaft (German Research Council)     

Steady-state vibration somatosensory evoked potentials: physiological characteristics and tuning function.

OBJECTIVE: The steady-state somatosensory evoked potentials (S-SEPs) to vibratory stimulation were recorded to characterize their physiological properties. METHODS: Vibratory stimuli were applied to the right palmar surface in 10 normal subjects. A total of 200 responses were recorded from electrodes at 2 cm posterior to C3, Cz and C4 and 2 cm anterior to C3. All responses were Fourier analyzed and the amplitudes of the first (1F) and second (2F) harmonic components were thus obtained. The effects of modulation frequency (5-30 Hz) and stimulus intensity (0.001-0.1 Newton (N)) on S-SEPs were studied. RESULTS: The amplitudes of 1F and 2F were greatest at the electrode 2 cm posterior to C3, 1F being predominant. The mean 1F amplitudes as a function of modulation frequency showed a bimodal distribution with a trough at 14 Hz and a peak at 21 Hz. The mean 1F amplitudes showed a linear increase of up to 0.05 N and thereafter reached a plateau against the logarithmic stimulus intensity axis. CONCLUSION: Vibratory S-SEPs may originate from the primary somatosensory cortex and provide information on the fast-adapting mechanoreceptive afferents. The temporal resonance at 21 Hz places the somatosensory system between the visual and auditory systems.     

Reliability in the assessment of paediatric somatosensory evoked potentials post cardiac arrest

ObjectiveTo measure inter- and intra-rater agreement in the interpretation of cortical somatosensory evoked potential (SSEP) components following paediatric cardiac arrest (CA) in multi-professional neurophysiology teams.MethodsThirteen professionals blinded to patient outcome interpreted 96 SSEPs in paediatric patients 24-/48-/72-hours following CA. Of these, 34 were duplicates used to assess intra-rater agreement. Consistent interpretations (absent/present/indeterminate) between scientists (who record/identify SSEP components) and neurophysiologists (who provide prognostic SSEP interpretation) were expressed as percentages. Rates of agreement were calculated using Fleiss’ kappa coefficient (K).ResultsUnanimous agreement between professionals was present in 40% (95%CI: 28–54%) of the interpreted SSEPs, with a K value of 0.62 (95%CI: 0.55–0.70) based on average agreement. Agreement was similar between neurophysiologists (K = 0.67; 95%CI: 0.57–0.77) and scientists (K = 0.62; 95%CI: 0.54–0.70) but lower in patients < 2 years old (K = 0.23; 95%CI: 0.14–0.33) and in those with poor outcome (K = 0.21; 95%CI: 0.07–0.35). No SSEP was unanimously interpreted as absent and 92% (95%CI: 89–95%) of duplicate SSEPs were interpreted consistently.ConclusionDespite substantial agreement when interpreting prognostic SSEPs, this was significantly lower in children with poor outcome and of younger age.SignificanceClinicians using SSEPs in the intensive care unit should be aware of the inter-rater variability when interpreting SSEPs as absent.     

Loss and spontaneous recovery of forelimb evoked potentials in both the adult rat cuneate nucleus and somatosensory cortex following contusive cervical spinal cord injury

Varying degrees of neurologic function spontaneously recovers in humans and animals during the days and months after spinal cord injury (SCI). For example, abolished upper limb somatosensory potentials (SSEPs) and cutaneous sensations can recover in persons post-contusive cervical SCI. To maximize recovery and the development/evaluation of repair strategies, a better understanding of the anatomical locations and physiological processes underlying spontaneous recovery after SCI is needed. As an initial step, the present study examined whether recovery of upper limb SSEPs after contusive cervical SCI was due to the integrity of some spared dorsal column primary afferents that terminate within the cuneate nucleus and not one of several alternate routes. C5-6 contusions were performed on male adult rats. Electrophysiological techniques were used in the same rat to determine forelimb evoked neuronal responses in both cortex (SSEPs) and the cuneate nucleus (terminal extracellular recordings). SSEPs were not evoked 2 days post-SCI but were found at 7 days and beyond, with an observed change in latencies between 7 and 14 days (suggestive of spared axon remyelination). Forelimb evoked activity in the cuneate nucleus at 15 but not 3 days post-injury occurred despite dorsal column damage throughout the cervical injury (as seen histologically). Neuroanatomical tracing (using 1% unconjugated cholera toxin B subunit) confirmed that upper limb primary afferent terminals remained within the cuneate nuclei. Taken together, these results indicate that neural transmission between dorsal column primary afferents and cuneate nuclei neurons is likely involved in the recovery of upper limb SSEPs after contusive cervical SCI.     

Auditory evoked potentials recorded intracranially from the brain stem in man

Auditory evoked potentials were recorded in patients undergoing neurosurgical operations to manage cranial nerve dysfunctions. Recordings were made intra-operatively from the distal portion of the eighth nerve, from the entrance of the eighth nerve into the brain stem, and from a site overlying the superior olivary complex (rostral and medial to the entrance of the eighth nerve). The potentials at the three different loci showed characteristic differences: the responses recorded at the entrance of the eighth nerve into the brain stem showed three peaks about 1 ms apart. The earliest peaks had longer latencies than did those recorded at a distal locus on the eighth nerve, which is consistent with what we know about propagation of nerve impulses in the auditory nerve. The responses recorded on the brain stem, rostral-medial to the eighth nerve, also showed three peaks but the amplitude of the third peak was greater than those of the other two. It is assumed that the first peak originates in the auditory nerve, the second peak in the cochlear nucleus, and the third peak in the lateral superior olive. The latencies of these peaks match the latencies of peaks II, III, and IV of scalp-recorded brain stem evoked potentials.     

Parkinsonian rest tremor can be detected accurately based on neuronal oscillations recorded from the subthalamic nucleus

Objective

To investigate the possibility of tremor detection based on deep brain activity.