Somatosensory Evoked Potentials Components Research Articles

Tactile imagery affects cortical responses to vibrotactile stimulation of the fingertip

Mental imagery is a crucial cognitive process, yet its underlying neural mechanisms remain less understood compared to perception. Furthermore, within the realm of mental imagery, the somatosensory domain is particularly underexplored compared to other sensory modalities. This study aims to investigate the influence of tactile imagery (TI) on cortical somatosensory processing. We explored the cortical manifestations of TI by recording EEG activity in healthy human subjects. We investigated event-related somatosensory oscillatory dynamics during TI compared to actual tactile stimulation, as well as somatosensory evoked potentials (SEPs) in response to short vibrational stimuli, examining their amplitude-temporal characteristics and spatial distribution across the scalp. EEG activity exhibited significant changes during TI compared to the no-imagery baseline. TI caused event-related desynchronization (ERD) of the contralateral μ-rhythm, with a notable correlation between ERD during imagery and real stimulation across subjects. TI also modulated several SEP components in sensorimotor and frontal areas, showing increases in the contralateral P100 and P300, contra- and ipsilateral P300, frontal P200, and parietal P600 components. The results clearly indicate that TI affects cortical processing of somatosensory stimuli, impacting EEG responses in various cortical areas. The assessment of SEPs in EEG could serve as a versatile marker of tactile imagery in practical applications. We propose incorporating TI in imagery-based brain-computer interfaces (BCIs) to enhance sensorimotor restoration and sensory substitution. This approach underscores the importance of somatosensory mental imagery in cognitive neuroscience and its potential applications in neurorehabilitation and assistive technologies.

Effects of inter-stimulus and inter-trial intervals on somatosensory gating

Aim of the study Sensory gating is a human higher cognitive function that serves to suppress excessive sensory information and prevent brain overactivity. To elucidate this function, a paired-pulse stimulation paradigm has been used while recording electroencephalography (EEG), and evaluated as an amplitude ratio of responses to a second stimulus (S2) over responses to the first stimulus (S1). The present study investigated the effects of the inter-stimulus interval (ISI) and inter-trial interval (ITI) on somatosensory gating using somatosensory-evoked potentials (SEPs). Methods In Experiment 1, ISI was set at five conditions: 200, 400, 600, 800, and 1000 ms. In Experiment 2, ITI was set at four conditions: 1, 2, 4, and 8 s. Results ISI affected the S2/S1 amplitude ratios of P22 and N27 at C3’ and N30 at Fz, and these S2/S1 amplitude ratios decreased the most under the 200 and 400-ms conditions. ITI affected the S2/S1 amplitude ratios of P22, N27, and N60 at C3', and especially, the somatosensory gating did not work under the 1-s condition. These results suggest that not all SEP components are modulated in the same manner with changing ISI and ITI. The effects of ISI and ITI independently affected the somatosensory gating. Conclusions Based on our findings, preferable parameters are 200-400 ms for ISI and 4 s or longer for ITI to evaluate the functional mechanisms on somatosensory gating in SEPs.

Facilitation of Early and Middle Latency SEP after tDCS of M1: No Evidence of Primary Somatosensory Homeostatic Plasticity

Homeostatic plasticity is a mechanism that stabilizes cortical excitability within a physiological range. Most homeostatic plasticity protocols have primed and tested the homeostatic response of the primary motor cortex (M1). This study investigated if a homeostatic response could be recorded from the primary sensory cortex (S1) after inducing homeostatic plasticity in M1. In 31 healthy participants, homeostatic plasticity was induced over M1 with a priming and testing block of transcranial direct current stimulation (tDCS) in two different sessions (anodal and cathodal). S1 excitability was assessed by early (N20, P25) and middle-latency (N33-P45) somatosensory evoked potentials (SEP) extracted from 4 electrodes (CP5, CP3, P5, P3). Baseline and post-measures (post-priming, 0-min, 10-min, and 20-min after homeostatic induction) were taken. Anodal M1 homeostatic plasticity induction significantly facilitated the N20-P25, P45 peak, and N33-P45 early SEP components up to 20-min post-induction, without any indication of a homeostatic response (i.e., reduced SEP). Cathodal homeostatic induction did not induce any significant effect on early or middle latency SEPs. M1 homeostatic plasticity induction by anodal stimulation protocol to the primary motor cortex did not induce a homeostatic response in SEPs.

Inter-hemispheric somatosensory coherence and parental stress in hypersensitivity at 8 months old: An electroencephalography study

ObjectiveInfant hypersensitivity affects daily challenges and parental stress. Although the crucial role of tactile sensation in infants' brain function has been highlighted, hypersensitive infants and their families lack support. Electroencephalography may be useful for understanding hypersensitivity traits. We investigated the relationship between infant perceptual hypersensitivity and parental stress, somatosensory-evoked potential (SEP), and magnitude-squared coherence (MSC) in the general population. MethodsInfants aged 8 months (n = 63) were evaluated for hypersensitivity and parental stress using a questionnaire and for cortical activity using electroencephalography. Vibration stimuli were applied to the infant’s left foot. SEP components that peaked around 150 ms (N2) and at 200 ms (P2) after stimulus onset were evaluated by amplitude and latency at the midline electrode (Cz) and MSC between the midline electrodes (C3–C4). ResultsParental stress was associated with infant hypersensitivity. The latency of Cz was delayed, and C3–C4 delta MSC was high in infants with hypersensitivity. ConclusionsIncreasing inter-hemispheric MSC synchrony in the stimulated condition in infants with hypersensitivity suggested atypical somatosensory cortical function. SignificanceThese findings contribute to identifying, understanding the mechanisms of, and developing effective coping strategies for early-stage hypersensitivity.

Does movement preparation enhance attending to bodily sensations in the back in people with persistent low back pain?

Attention has been proposed to play an important role in persisting pain, with excessive attentional processes towards pain information leading to worse pain outcomes and maladaptive behaviors. Nevertheless, research on somatosensory attending during the anticipation of pain-related movements is still scarce. This study investigated if individuals with chronic and recurrent lower back pain compared to pain-free controls, show enhanced attending to somatosensory information in the back while anticipating back-recruiting movements. 43 healthy control, 33 recurrent (RLBP) and 33 chronic low back (CLBP) pain sufferers were asked to perform back-recruiting movements. Before the movement initiation cue, a task-irrelevant tactile stimulus was administered to participants' lower back to elicit somatosensory evoked potentials (SEPs), used as an index of somatosensory attending. In contrast to our hypothesis, most identified SEP components did not differ across groups. The only exception was the P175 amplitude which was larger for the CLBP group compared to individuals with RLBP and healthy controls. The current study did not find robust evidence of enhanced somatosensory attending to the back in people with persisting lower back pain. The finding that CLBP, but not RLBP individuals, had larger amplitudes to the P175 component, is discussed as possibly reflecting a higher state of emotional arousal in these patients when having to prepare the back-recruiting movements.

Movement predictability modulates sensorimotor processing.

An important factor for optimal sensorimotor control is how well we are able to predict sensory feedback from internal and external sources during movement. If predictability decreases due to external disturbances, the brain is able to adjust muscle activation and the filtering of incoming sensory inputs. However, little is known about sensorimotor adjustments when predictability is increased by availability of additional internal feedback. In the present study we investigated how modifications of internal and external sensory feedback influence the control of muscle activation and gating of sensory input. Co-activation of forearm muscles, somatosensory evoked potentials (SEP) and short afferent inhibition (SAI) were assessed during three object manipulation tasks designed to differ in the predictability of sensory feedback. These included manipulation of a shared object with both hands (predictable coupling), manipulation of two independent objects without (uncoupled) and with external interference on one of the objects (unpredictable coupling). We found a task-specific reduction in co-activation during the predictable coupling compared to the other tasks. Less sensory gating, reflected in larger subcortical SEP amplitudes, was observed in the unpredictable coupling task. SAI behavior was closely linked to the subcortical SEP component indicating an important function of subcortical sites in predictability related SEP gating and their direct influence on M1 inhibition. Together, these findings suggest that the unpredictable coupling task cannot only rely on predictive forward control and is compensated by enhancing co-activation and increasing the saliency for external stimuli by reducing sensory gating at subcortical level. This behavior might serve as a preparatory step to compensate for external disturbances and to enhance processing and integration of all incoming external stimuli to update the current sensorimotor state. In contrast, predictive forward control is accurate in the predictable coupling task due to the integrated sensory feedback from both hands where sensorimotor resources are economized by reducing muscular co-activation and increasing sensory gating.

Skin type and nerve effects on cortical tactile processing: a somatosensory evoked potentials study.

Somatosensory evoked potentials (SEP) studies typically characterize short latency components following median nerve stimulations of the wrist. However, these studies rarely considered 1) skin type (glabrous/hairy) at the stimulation site, 2) nerve being stimulated, and 3) middle latency (>30 ms) components. Our aim was to investigate middle latency SEPs following simple mechanical stimulation of two skin types innervated by two different nerves. 18 adults received 400 mechanical stimulations over four territories of the right hand (two nerves: radial/median; two skin types: hairy/glabrous skin) while their EEG was recorded. Four middle latency components were identified: P50, N80, N130 and P200. As expected, significantly shorter latencies and larger amplitudes were found over the contralateral hemisphere for all components. A skin type effect was found for the N80: glabrous skin stimulations induced larger amplitude than hairy skin stimulations. Regarding nerve effects, median stimulations induced larger P50 and N80. Latency of the N80 was longer after median nerve stimulation compared to radial nerve stimulation. This study showed that skin type and stimulated nerve influence middle latency SEPs, highlighting the importance of considering these parameters in future studies. These modulations could reflect differences in cutaneous receptors and somatotopy. Middle latency SEPs can be used to evaluate the different steps of tactile information cortical processing. Modulation of SEPs components before 100 milliseconds possibly reflects somatotopy and differential processing in SI cortex.

Clinical-immunological and neurophysiological correlations in paraneoplastic polyneuropathy caused by small cell lung cancer

Objective. To study the correlation between the neurological, immunological and neurophysiological signs of paraneoplastic polyneuropathy (PPNP) caused by small cell lung cancer (SCLC), to improve the quality of diagnosis of this pathology.Materials and methods. Clinical, immunological (anti-Hu) and neurophysiological (electromyography (EMG), electroneuromyography (ENMG), somatosensory evoked potentials (SSEP)) examination of 61 patients with PPNP caused by SCLC are presented.Results. It was established that sensory disorders in the limbs are the first and obligate clinical symptoms of PPNP, which precede the initial diagnosis of SCLC in 56% in 3-12 months, characterized by a predominance of a decrease in surface sensitivity in the form of distal hypoesthesia in 70% of cases. The motor form is characterized by an older age (67 years) than the sensory (60 years) and sensorimotor (58.0 years, p <0,05). Motor disorders in the limbs occur in 46% of cases, manifested by mild symmetrical distal paresis of the legs and subclinical damage to the motor nerves of the upper extremities according to the results of ENMG (p <0,001). Detection of anti-Hu in plasma is highly correlated with a significant increase in latency and a decrease in amplitudes component N22 in the conduct of SSEP, which indicates the defeat of the axons of the sensory nerves of the limbs (p <0,05). Changes in amplitude parameters, with preserved speed indicators of nerves according to the results of ENMG indicate an axonal type of lesion (p <0,05), which, in combination with the detection of anti-Hu in plasma, are pathognomonic signs of the paraneoplastic nature of the process.Conclusion. As a result of the study, clinical, immunological and neurophysiological features of various forms of PPNP were identified. The obtained correlations make it possible to diagnose the corresponding type of nerve pathology more accurately and in a timely manner and to suspect the development of oncological disease in time. The revealed changes in the indicators of the N22 component of SSEP can serve as a marker of axonal lesion of peripheral nerves, which with high diagnostic efficiency justifies the expediency of inclusion in the protocol of the ENMG study for verification of additional signs characteristic of PPNP.

Cutaneous information processing differs with load type during isometric finger abduction.

During submaximal isometric contraction, there are two different load types: maintenance of a constant limb angle while supporting an inertial load (position task) and maintenance of a constant force by pushing against a rigid restraint (force task). Previous studies demonstrated that performing the position task requires more proprioceptive information. The purpose of this study was to investigate whether there would be a difference in cutaneous information processing between the position and force tasks by assessing the gating effect, which is reduction of amplitude of somatosensory evoked potentials (SEPs), and cutaneomuscular reflex (CMR). Eighteen healthy adults participated in this study. They contracted their right first dorsal interosseous muscle by abducting their index finger to produce a constant force against a rigid restraint that was 20% maximum voluntary contraction (force task), or to maintain a target position corresponding to 10° abduction of the metacarpophalangeal joint while supporting a load equivalent to 20% maximum voluntary contraction (position task). During each task, electrical stimulation was applied to the digital nerves of the right index finger, and SEPs and CMR were recorded from C3' of the International 10-20 system and the right first dorsal interosseous muscle, respectively. Reduction of the amplitude of N33 component of SEPs was significantly larger during the force than position task. In addition, the E2 amplitude of CMR was significantly greater for the force than position task. These findings suggest that cutaneous information processing differs with load type during static muscle contraction.

Cortical Reorganization of Early Somatosensory Processing in Hemiparetic Stroke.

The cortical motor system can be reorganized following a stroke, with increased recruitment of the contralesional hemisphere. However, it is unknown whether a similar hemispheric shift occurs in the somatosensory system to adapt to this motor change, and whether this is related to movement impairments. This proof-of-concept study assessed somatosensory evoked potentials (SEPs), P50 and N100, in hemiparetic stroke participants and age-matched controls using high-density electroencephalograph (EEG) recordings during tactile finger stimulation. The laterality index was calculated to determine the hemispheric dominance of the SEP and re-confirmed with source localization. The study found that latencies of P50 and N100 were significantly delayed in stroke brains when stimulating the paretic hand. The amplitude of P50 in the contralateral (to stimulated hand) hemisphere was negatively correlated with the Fügl-Meyer upper extremity motor score in stroke. Bilateral cortical responses were detected in stroke, while only contralateral cortical responses were shown in controls, resulting in a significant difference in the laterality index. These results suggested that somatosensory reorganization after stroke involves increased recruitment of ipsilateral cortical regions, especially for the N100 SEP component. This reorganization delays the latency of somatosensory processing after a stroke. This research provided new insights related to the somatosensory reorganization after stroke, which could enrich future hypothesis-driven therapeutic rehabilitation strategies from a sensory or sensory-motor perspective.

Effects of short-term upper limb immobilization on sensory information processing and corticospinal excitability.

Several studies have reported the effects of short-term immobilization of the upper limb on the excitability of the primary motor cortex. In a report examining the effects of upper limb immobilization on somatosensory information processing using somatosensory-evoked potentials (SEPs), short-term upper limb immobilization reduced the amplitude and increased the latency of the P45 component recorded over the contralateral sensorimotor cortex of SEPs. However, the effects of upper limb immobilization on other regions involved in somatosensory information processing are unknown. Therefore, we investigated the effects of short-term right upper limb immobilization on sensory information processing, particularly in motor-related areas, by measuring the cortical components of SEPs. We also evaluated the excitability of the primary motor cortex and corticospinal tract as well as motor performance (visual simple reaction time and pinch force) related to these areas. All subjects were divided into two groups: the SEP group, in which the effects of upper limb immobilization on the excitability of somatosensory processing were investigated, and the transcranial magnetic stimulation (TMS) group, in which the effects of upper limb immobilization on the excitability of the corticospinal tract and primary motor cortex were investigated. Motor performance was evaluated in all subjects. We showed that 10-h right upper limb immobilization increased the cortical component of SEPs (N30) in the SEP group and decreased the excitability of the corticospinal tract, but not of the primary motor cortex, in the TMS group. The pinch force decreased after upper limb immobilization. However, the visual simple reaction time did not change between pre- and post-immobilization. The supplementary motor area and premotor cortex are believed to be the source of the N30. Therefore, these results suggest that upper limb immobilization affected somatosensory information processing in motor-related areas. Moreover, 10-h right upper limb immobilization reduced the excitability of corticospinal tracts but not that of the primary motor cortex, suggesting that circuits outside the M1, such as the intra- and inter-hemispheric inhibitory and facilitatory circuits rather than circuits within the M1, may be responsible for the reduced excitability of the central nervous system after restraint.

Corticospinal excitability and somatosensory information processing of the lower limb muscle during upper limb voluntary or electrically induced muscle contractions.

Neural interactions between upper and lower limbs underlie motor coordination in humans. Specifically, upper limb voluntary muscle contraction can facilitate spinal and corticospinal excitability of the lower limb muscles. However, little remains known on the involvement of somatosensory information in arm-leg neural interactions. Here, we investigated effects of voluntary and electrically induced wrist flexion on corticospinal excitability and somatosensory information processing of the lower limbs. In Experiment 1, we measured transcranial magnetic stimulation (TMS)-evoked motor evoked potentials (MEPs) of the resting soleus (SOL) muscle at rest or during voluntary or neuromuscular electrical stimulation (NMES)-induced wrist flexion. The wrist flexion force was matched to 10% of the maximum voluntary contraction (MVC). We found that SOL MEPs were significantly increased during voluntary, but not NMES-induced, wrist flexion, compared to the rest (P < .001). In Experiment 2, we examined somatosensory evoked potentials (SEPs) following tibial nerve stimulation under the same conditions. The results showed that SEPs were unchanged during both voluntary and NMES-induced wrist flexion. In Experiment 3, we examined the modulation of SEPs during 10%, 20% and 30% MVC voluntary wrist flexion. During 30% MVC voluntary wrist flexion, P50-N70 SEP component was significantly attenuated compared to the rest (P = .003). Our results propose that the somatosensory information generated by NMES-induced upper limb muscle contractions may have a limited effect on corticospinal excitability and somatosensory information processing of the lower limbs. However, voluntary wrist flexion modulated corticospinal excitability and somatosensory information processing of the lower limbs via motor areas.

Transcranial alternating current stimulation modulates cortical processing of somatosensory information in a frequency- and time-specific manner

Neural oscillations can be modulated by non-invasive brain stimulation techniques, including transcranial alternating current stimulation (tACS). However, direct evidence of tACS effects at the cortical level in humans is still limited. In a tACS-electroencephalography co-registration setup, we investigated the ability of tACS to modulate cortical somatosensory information processing as assessed by somatosensory-evoked potentials (SEPs). To better elucidate the neural substrates of possible tACS effects we also recorded peripheral and spinal SEPs components, high-frequency oscillations (HFOs), and long-latency reflexes (LLRs). Finally, we studied whether changes were limited to the stimulation period or persisted thereafter. SEPs, HFOs, and LLRs were recorded during tACS applied at individual mu and beta frequencies and at the theta frequency over the primary somatosensory cortex (S1). Sham-tACS was used as a control condition. In a separate experiment, we assessed the time course of mu-tACS effects by recording SEPs before (T0), during (T1), and 1 min (T2) and 10 min (T3) after stimulation. Mu-tACS increased the amplitude of the N20 component of SEPs compared to both sham and theta-tACS. No differences were found between sham, beta-, and theta-tACS conditions. Also, peripheral and spinal SEPs, P25, HFOs, and LLRs did not change during tACS. Finally, mu-tACS-induced modulation of N20 amplitude specifically occurred during stimulation (T1) and vanished afterwards (i.e., at T2 and T3). Our findings suggest that TACS applied at the individual mu frequency is able to modulate early somatosensory information processing at the S1 level and the effect is limited to the stimulation period.

Comparison of the therapeutic effects of erythropoietin and acetyl-l-carnitine on sciatic nerve injury in rats

ABSTRACT Aim We aimed to investigate the effects of erythropoietin, acetyl-l-carnitine, and their combination on nerve regeneration in experimental peripheral nerve injury. Methods Rats were randomly divided into five groups – sham-operated (S), sciatic nerve crush injury (C), C + acetyl-l-carnitine (ALCAR), C + erythropoietin (EPO), and C + EPO + ALCAR. ALCAR (50 mg/kg/day) was administered intraperitoneally, and EPO (5000 U/kg) was injected subcutaneously for 10 days. Functional recovery was evaluated using walking track analysis (sciatic functional index [SFI]), somatosensory evoked potentials (SEPs), thiobarbituric acid reactive substance (TBARS) assay, and caspase-3 and S100 immunoreactivities. Results In SFI analyses, delayed functional recovery was observed in the C group, whereas the functional recovery of rats treated with EPO and ALCAR significantly improved. The latencies of the SEP components were significantly prolonged in C group. In the treatment groups (C + EPO, C + ALCAR, and C + EPO + ALCAR), all recorded values of SEP components significantly decreased. TBARS levels in C group were significantly higher than those in the S group. EPO and ALCAR administration significantly decreased TBARS levels. Caspase-3 immunoreactivity was increased in the C group, whereas it was decreased in the treatment groups. S100 immunolabelling was significantly decreased in the C group. EPO and ALCAR administration caused an increase in the amount of S100-positive cells in all treatment groups. Conclusion EPO and ALCAR administration could accelerate sciatic nerve repair by reducing apoptosis and lipid peroxidation and promoting myelinization. Although both EPO and ALCAR had positive effects on nerve healing, their combined efficacy had no statistically significant effect on peripheral nerve regeneration.

Reconstructing subcortical and cortical somatosensory activity via the RAMUS inverse source analysis technique using median nerve SEP data

This study concerns reconstructing brain activity at various depths based on non-invasive EEG (electroencephalography) scalp measurements. We aimed at demonstrating the potential of the RAMUS (randomized multiresolution scanning) technique in localizing weakly distinguishable far-field sources in combination with coinciding cortical activity. As we have shown earlier theoretically and through simulations, RAMUS is a novel mathematical method that by employing the multigrid concept, allows marginalizing noise and depth bias effects and thus enables the recovery of both cortical and subcortical brain activity. To show this capability with experimental data, we examined the 14–30 ms post-stimulus somatosensory evoked potential (SEP) responses of human median nerve stimulation in three healthy adult subjects. We aim at reconstructing the different response components by evaluating a RAMUS-based estimate for the primary current density in the nervous tissue. We present source reconstructions obtained with RAMUS and compare them with the literature knowledge of the SEP components and the outcome of the unit-noise gain beamformer (UGNB) and standardized low-resolution brain electromagnetic tomography (sLORETA). We also analyzed the effect of the iterative alternating sequential technique, the optimization technique of RAMUS, compared to the classical minimum norm estimation (MNE) technique. Matching with our previous numerical studies, the current results suggest that RAMUS could have the potential to enhance the detection of simultaneous deep and cortical components and the distinction between the evoked sulcal and gyral activity.

A new, sensitive biomarker for abnormal cortical excitability: Single trial based synchronization and desynchronization with cortical myoclonus

Giant somatosensory evoked potentials (SEPs), i.e., enlarged cortical components of SEPs, represent abnormal cortical excitability such as cortical myoclonus (CM). Recently, we reported high-frequency oscillations (HFOs) with a part of giant SEPs specifically observed in benign adult familial myoclonus epilepsy (Tojima et al., 2021). However, no clear HFOs after N33 were observed. We herein hypothesized, in CM patients, late cortical abnormal excitability may be poorly synchronized in average method and thus only detectable by single trial, event-related synchronization (ERS) and desynchronization (ERD). We also compared ERS/ERD between CM patients and healthy controls (HCs).

Somatosensory Gating Is Modulated by Anodal Transcranial Direct Current Stimulation.

BackgroundAnodal transcranial direct current stimulation (tDCS) of the somatosensory cortex causes cerebral hyperexcitability and a significant enhancement in pain thresholds and tactile spatial acuity. Sensory gating is a brain mechanism to suppress irrelevant incoming inputs, which is elicited by presenting pairs of identical stimuli (S1 and S2) within short time intervals between stimuli (e.g., 500 ms).Objectives/HypothesisThe present study addressed the question of whether tDCS could modulate the brain correlates of this inhibitory mechanism.MethodsForty-one healthy individuals aged 18–26 years participated in the study and were randomly assigned to tDCS (n = 21) or SHAM (n = 20). Somatosensory evoked potentials (SEP) elicited by S1 and S2 pneumatic stimuli (duration of 100 ms, ISI 550 ± 50 ms) and applied to the index finger of the dominant hand were recorded before and after tDCS.ResultsBefore the intervention, the second tactile stimuli significantly attenuated the amplitudes of P50, N100, and the late positive complex (LPC, mean amplitude in the time window 150–350) compared to the first stimuli. This confirmed that sensory gating is a widespread brain inhibitory mechanism that can affect early- and middle-latency components of SEPs. Furthermore, our data revealed that this response attenuation or sensory gating (computed as S1 minus S2) was improved after tDCS for LPC, while no changes were found in participants who received SHAM.ConclusionAll these findings suggested that anodal tDCS might modulate brain excitability leading to an enhancement of inhibitory mechanisms elicited in response to repetitive somatosensory stimuli during late stages of information processing.

P-EP028. Low-dose perampanel improves refractory cortical myoclonus by the dispersed and suppressed paroxysmal depolarization shifts in the sensorimotor cortex

Introduction. Although low-dose perampanel (PER) is reportedly effective on cortical myoclonus in a limited number of patients, its underlying mechanisms remain unclear. We aimed to extract and elaborate the clinical effects of PER on refractory cortical myoclonus for dose, etiology and also somatosensory-evoked potential (SEP) findings. Method. We examined 18 epilepsy patients with seizure and cortical myoclonus (10 males; mean age, 48.4 ± 16.2 years; Unverricht-Lundborg disease = 7, benign adult familial myoclonus epilepsy = 6, dentatorubral-pallidoluysian atrophy = 2, Gaucher disease = 1, and Lance-Adams syndrome = 2). Based on data accumulated before and after PER treatment, activities of daily life [ADL]), short latency, cortical components of SEP, and PER blood concentration were analyzed. Results. PER (mean dose: 3.2 ± 2.1 mg/day) significantly improved seizure frequency, myoclonus and ADL scores. It also significantly decreased the amplitude of and prolonged correlate with clinical scores among all patients. In contrast, the degree of P25 prolongation ms) significantly correlated with improved ADL score (p = 0.019) and blood PER concentration (p = 0.011). The degree of N33 prolongation (32.1 ± 4.0 to 33.7 ± 3.4 ms) was positively correlated with ADL score and blood PER concentration (p = 0.025 and p = 0.025, respectively). Conclusion. Low-dose PER markedly improved myoclonus and ADL in patients with refractory cortical myoclonus. SEP, especially P25 latency, is a potentially good biomarker to assess the objective effects of PER on intractable cortical myoclonus. ( https://doi.org/10.1016/j.clinph.2019.07.006 ).

Heartbeat and somatosensory perception

Our perception of the external world is influenced by internal bodily signals. For example, we recently showed that timing of stimulation along the cardiac cycle and spontaneous fluctuations of heartbeat-evoked potential (HEP) amplitudes influence somatosensory perception and the associated neural processing (Al et al., 2020). While cardiac phase affected detection sensitivity and late components of the somatosensory-evoked potentials (SEPs), HEP amplitudes affected detection criterion and both early and late SEP components. In a new EEG study, we investigate whether these results are replicable in a modified paradigm, which includes two succeeding temporal intervals. In one of the intervals, subjects received a weak electrical finger stimulation and reported first whether they detected any stimulation and then allocated the stimulus to one of the two intervals. Our results confirm the previously reported cardiac cycle and prestimulus HEP effects on somatosensory perception and evoked potentials. In addition, we obtained two new findings. Source analyses in this and our original study show that the increased likelihood of conscious perception goes along with HEP fluctuations in parietal and posterior cingulate regions, known to play important roles in interoceptive processes. Furthermore, HEP amplitudes were shown to decrease when subjects engaged in the somatosensory task compared to a resting state condition. Our findings are consistent with the view that HEP amplitudes are a marker of interoceptive (versus exteroceptive) attention and provide a neural underpinning for this view.

Relative and absolute reliability of somatosensory evoked potentials in response to non-noxious electrical stimulation of the paraspinal muscles in healthy participants at an interval of 3-months

Background Somatosensory evoked potentials (SEPs) are used extensively to quantify cortical activity in response to noxious and/or non-noxious sensory stimuli. However, data demonstrating the reliability of SEP measures in response to non-noxious stimulation over time are scarce. Aim We investigated the relative and absolute reliability, and the smallest detectable change at 95% confidence (SDC95) for SEPs evoked by non-noxious electrical stimulation of the paraspinal muscles in thirty-nine healthy participants at a 3-month interval. Methods SEPs were evoked at an intensity three-times that of each participant's perceptual threshold and recorded from a single electrode placed over the primary somatosensory cortex (S1). Results Our analyses reveal that i) latency, as a measure of activity onset, has poor relative reliability but good absolute reliability; ii) area, as a measure of cortical activity, has good relative and absolute reliability (except for the N150 component) and iii) perceptual threshold and stimulation intensity was not reliable over time. Conclusion These findings suggest that the area of the N80 and P260 SEP components, and the area of the N80-N150-P260 SEP complex, can be utilised in future studies as reliable markers of cortical activity.