Synthesis and characterization of a (+)-catechin and L-(+)-ascorbic acid cocrystal as a new functional ingredient for tea drinks

Tea (Camellia Sinensis) is one of the most popular drink, consumed as infusion or bottled ready to drink beverages. Although tea leaves contain many antioxidants compounds, after processing they can drastically decrease, sometimes up to a full degradation, as in the case of catechin, a very healthy flavan-3-ol. In this context, the synthesis of a cocrystal between (+)-catechin and L-(+)-ascorbic acid, was proved to be a useful strategy to make a new ingredient able to ameliorate the antioxidant profile of both infusions and bottled teas. The obtained cocrystal showed a three-fold higher solubility than (+)catechin and its formation was elucidated unambiguously by FT-IR, thermal (DSC) and diffraction (PXRD) analyses. Antioxidant characteristics of the samples were evaluated by colorimetric assays. As expected, infusions showed much better antioxidant features than ready-to-use lemon and peach teas. The same trend was confirmed after the addition of the cocrystal at two concentration levels. In particular, supplementation at concentration of 2 mg mL-1 improved the bottled tea antioxidant values to the level showed by the not-added infusion tea.

Bioremediation of Food Industry Effluents: Recent Applications of Free and Immobilised Polyphenoloxidases

Enzymes are specific biological catalysts able to react under mild conditions of temperature and pH and their use in food industry for bioremediation is well known. Research in recent years has been intense, much of it elicited by the great number of different exploitable enzymes. Employment of enzymes in many bioremediation processes is made in order to protect the environment from damage caused by industrial polluting effluents. In particular, the food industry is one of the most important sectors among the manufacturing industries as far as production values are concerned; indeed, food industry processes involve large amounts of water and contribute to pollution loads discharged into water resources. In particular the presence of phenols in agroindustrial effluents has attracted interest for laccases and tyrosinases use in wastewater treatment and bioremediation. The presence of phenolic compounds in drinking and irrigation water or in cultivated land represents a significant health and/or environmental hazard and, therefore, the development of methods for their removal and transformation have received increased attention in recent years. The main purpose of this paper was to present the most recent results dealing with the fundamental and applied aspects of free and immobilised polyphenoloxidases for food industry wastewater processing.

Inhibitory effect of voluntary movement preparation on cutaneous heat pain and laser-evoked potentials

In our study, preparation of voluntary movement was used to physiologically activate the motor cortex areas and the effect of this activation on CO(2) laser-evoked potentials (LEPs) was explored. LEPs were recorded from 31 scalp electrodes in 10 healthy subjects after painful stimulation of the right C6-C7 skin dermatomes. LEP stimuli were delivered in the time interval between a visual warning stimulus followed after 1 s. by an imperative stimulus. The imperative stimulus triggered: (i) no task in the baseline condition (Pain); (ii) flexion-extension movements of the second finger of the right hand in the movement condition (Pain + Movement); (iii) cognitive task (mathematic computation) in the distraction condition (Pain + Cognition). The experimental conditions were also repeated during application of laser stimuli on the left C6-C7 skin dermatomes. Compared with the baseline condition (no task required), during preparation of right-hand voluntary movement there was a significant reduction in LEP amplitude and subjective pain rating after right- but not after left-hand stimulation, which suggests that the observed effect cannot be attributed to a nonspecific reduction in attention toward painful stimulus. During preparation of a cognitive task, LEP amplitude was reduced compared to baseline. Our results represent the first neurophysiological suggestion that physiological activation of the motor cortex, occurring during movement preparation, inhibits cortical pain processing by a centrifugal mechanism.

Modulation of laser-evoked potentials by experimental cutaneous tonic pain

The present study aimed to investigate whether tonic cutaneous pain exerts any effect on the cortical processing of nociceptive input and if this effect may involve only body parts in pain. Tonic cutaneous pain was obtained in nine healthy human subjects by infusion of a hypertonic saline (5%) in the s.c. tissue over the hypothenar muscles (10 ml/h for 20 min). Nociceptive cutaneous CO2 laser-evoked potentials were recorded after stimulation of the right hand dorsum, which was adjacent to the painful area, and the right perioral region, corresponding to the adjacent cortical sensory area. Laser-evoked potentials were obtained before saline injection, at the peak pain and 20 min after pain disappeared. During saline infusion, the laser-evoked pain to right hand stimulation was reduced and the vertex laser-evoked potentials (N2a-P2, mean latency 181 ms and 319 ms for the N2a and the P2 potentials, respectively), which are generated in the anterior cingulate cortex, were significantly decreased in amplitude compared with the baseline. Moreover, the topography of these potentials was modified by cutaneous pain, shifting from the central toward the parietal region. Dipolar modeling showed that the dipolar source in the anterior cingulate cortex moved backward during saline infusion. This result suggests that cutaneous pain may modify the relative activities of the anterior and posterior anterior cingulate cortex parts, which are thought to be devoted to encode different aspects of pain sensation. No laser-evoked potential change was observed after stimulation of the right perioral region, suggesting that functional changes in the nociceptive system are selective for the painful regions and not for areas with cortical proximity.

Tensor veli palatini electromyography with surface electrode applied transnasally

A new technique is proposed for paratubal electromyography, using a surface, non-invasive, electrode applied transnasally under nasopharyngoscope guidance. This electrode records activity of the tensor veli palatini muscle during swallowing. This technique is of interest for two reasons: endoscopic guidance offers the possibility to check correct positioning of the electrode recording at tensor veli palatini muscle level. Introduction of the non-invasive surface electrode is simple and not painful.

Segmental inhibition of cutaneous heat sensation and of laser-evoked potentials by experimental muscle pain

The aim of the study was to evaluate the effect of tonic muscle pain evoked by injection of 5% hypertonic saline in the right brachioradialis muscle on the somatosensory sensation of laser-evoked heat pain and laser-evoked potentials. The heat pain pathways were studied in 9 healthy human subjects by recording the scalp potentials evoked by CO(2) laser stimuli delivered on four sites: the skin above the right brachioradialis muscle (ipsilateral local pain), the wrist area where muscle pain was referred in all subjects (ipsilateral referred pain), and two areas on the left arm symmetrical to both local and referred pain (contralateral local pain and contralateral referred pain). Laser-evoked potentials were obtained from 31 scalp electrodes before saline injection, during saline infusion (bolus injection with 0.3 ml saline infused over 20 s, followed by a steady infusion rate of 30 ml/h for the next 25 min), and 20 min after muscle pain had disappeared. While the early N1/P1 component (around 130 ms and 145 ms of latency after stimulation of the skin over the brachioradialis muscle and the wrist, respectively) was not affected by muscle pain, the amplitudes of the later vertex laser-evoked potentials (N2 latency of around 175 ms and 210 ms after stimulation of the skin over the brachioradialis muscle and the wrist, respectively; P2 latency of around 305 ms and 335 ms after stimulation of the skin over the brachioradialis muscle and the wrist, respectively) evoked from ipsilateral local pain, ipsilateral referred pain, and contralateral local pain sites were significantly decreased during muscle pain compared with the baseline recording, while they recovered after pain had disappeared. At the same stimulation sites, the rating of the laser-evoked pain sensation was reduced significantly during muscle pain as compared with the baseline and it recovered after pain had disappeared. On the contrary, muscle pain did not show any effect on both laser-evoked pain and laser-evoked potential amplitude when the contralateral referred pain site was stimulated. The muscle pain inhibitory effect on both heat pain sensation and laser-evoked potential amplitude is probably mediated by an ipsilateral and contralateral segmental mechanism which acts also on the referred pain area, while more general inhibitory mechanisms, such as a distraction effect or a diffuse noxious inhibitory control, are excluded by the absence of any effect of muscle pain on laser-evoked pain and laser-evoked potentials obtained from a remote site, such as the contralateral referred pain area. Since muscle pain induced by hypertonic saline injection is very similar to clinical pain, our results can be useful in understanding the pathophysiology of the somatosensory modifications which can be observed in patients with musculoskeletal pain syndromes.

Parietal generators of low- and high-frequency MN (median nerve) SEPs: data from intracortical human recordings

OBJECTIVE

To identify low and high-frequency median nerve (MN) somatosensory evoked potential (SEP) generators by means of chronically implanted electrodes in the parietal lobe (SI and neighbouring areas) of two epileptic patients.

METHODS

Wide-pass short-latency and long-latency SEPs to electrical MN stimulation were recorded in two epileptic patients by stereotactically chronically implanted electrodes in the parietal lobe (SI and neighbouring areas). To study high-frequency responses (HFOs) an off-line digital filtering of depth short-latency SEPs was performed (500-800 Hz, 24 dB roll-off). Spectral analysis was performed by fast Fourier transform.

RESULTS

In both patients we recorded a N20/P30 potential followed by a biphasic N50/P70 response. A little negative response in the 100 ms latency range was the last detectable wide-pass SEP in both patients. Two HFOs components (called iP1 and iP2) were detected by mere visual analysis and spectral analysis, and were supposed to be originated within the parietal cortex.

CONCLUSIONS

This was the very first study that recorded wide bandpass and high frequency SEPs by electrodes, exploring both the lateral and the mesial part of the parietal lobe and particularly that of the post-central gyrus.

Reduced habituation to experimental pain in migraine patients: a CO2 laser evoked potential study

The habituation to sensory stimuli of different modalities is reduced in migraine patients. However, the habituation to pain has never been evaluated. Our aim was to assess the nociceptive pathway function and the habituation to experimental pain in patients with migraine. Scalp potentials were evoked by CO(2) laser stimulation (laser evoked potentials, LEPs) of the hand and facial skin in 24 patients with migraine without aura (MO), 19 patients with chronic tension-type headache (CTTH), and 28 control subjects (CS). The habituation was studied by measuring the changes of LEP amplitudes across three consecutive repetitions of 30 trials each (the repetitions lasted 5 min and were separated by 5-min intervals). The slope of the regression line between LEP amplitude and number of repetitions was taken as an index of habituation. The LEPs consisted of middle-latency, low-amplitude responses (N1, contralateral temporal region, and P1, frontal region) followed by a late, high-amplitude, negative-positive complex (N2/P2, vertex). The latency and amplitude of these responses were similar in both patients and controls. While CS and CTTH patients showed a significant habituation of the N2/P2 response, in MO patients this LEP component did not develop any habituation at all after face stimulation and showed a significantly lower habituation than in CS after hand stimulation. The habituation index of the vertex N2/P2 complex exceeded the normal limits in 13 out of the 24 MO patients and in none of the 19 CTTH patients (P<0.0001; Fisher's exact test). Moreover, while the N1-P1 amplitude showed a significant habituation in CS after hand stimulation, it did not change across repetitions in MO patients. In conclusion, no functional impairment of the nociceptive pathways, including the trigeminal pathways, was found in either MO or CTTH patients. But patients with migraine had a reduced habituation, which probably reflects an abnormal excitability of the cortical areas involved in pain processing.

Influence of cholinergic circuitries in generation of high-frequency somatosensory evoked potentials

OBJECTIVE

High-frequency oscillations (HFOs) evoked by upper limb stimulation reflect highly synchronised spikes generated in the somatosensory human system. Since acetylcholine produces differential modulation in subgroups of neurons, we would determine whether cholinergic drive influences HFOs.

METHODS

We recorded somatosensory evoked potentials (SEPs) from 31 scalp electrodes in 7 healthy volunteers, before and after single administration of rivastigmine, an inhibitor of central acetylcholinesterase. Right median nerve SEPs have been analysed after digital narrow bandpass filtering (500-700 Hz). Raw data were further submitted to Brain Electrical Source analysis (BESA) to evaluate the respective contribution of lemniscal, thalamic and cortical sources. Lastly, we analysed by Fast Fourier transform spectral changes after drug administration in the 10-30 ms latency range.

RESULTS

Rivastigmine administration caused a significant increase of HFOs in the 18-28 ms latency range. Wavelets occurring before the onset latency of the conventional N20 SEP did not show any significant change. A similar increase concerned the strength of cortical dipolar sources in our BESA model. Lastly, we found a significant power increase of the frequency peak at about 600 Hz in P3-F3 traces after drug intake.

CONCLUSIONS

Our findings demonstrate that the cortical component of HFOs is significantly enhanced by cholinergic activation. Pyramidal chattering cells, which are capable to discharge high-frequency bursts, are mainly modulated by cholinergic inputs; by contrast, acetylcholine does not modify the firing rate of fast-spiking GABAergic interneurons. We thus discuss the hypothesis that cortical HFOs are mainly generated by specialised pyramidal cells.

The human supplementary motor area-proper does not receive direct somatosensory inputs from the periphery: data from stereotactic depth somatosensory evoked potential recordings

Somatosensory evoked potentials to median nerve (MN) stimulation were recorded by stereotactically implanted electrodes in the frontal lobe of two epileptic patients in order to evaluate whether short-latency cortical responses could be generated in the supplementary motor area (SMA)-proper. In both patients two potentials, called P20 and N30 responses, showed a decreasing amplitude from the most superficial to the deepest contacts and were recorded in the white as well in the grey matter of the frontal lobe. Furthermore, no phase reversal of both P20 and N30 potentials was identifiable along electrode trajectories. Our results suggest that short-latency somatosensory evoked responses recorded in the SMA-proper contralateral to MN stimulation are volume conducted from remote cortical generators.

Cervical cord dysfunction during neck flexion in Hirayama's disease

Neck flexion may play a role in the pathogenesis of Hirayama disease. Upper limb somatosensory evoked potentials were recorded in five patients with Hirayama disease, six patients with ALS, and 14 healthy subjects. Neck flexion caused a significant amplitude decrease of the N13 cervical response only in patients with Hirayama disease. Direct cord compression or microvascular changes can in theory account for this position-related dysfunction.

Contribution of GABAergic cortical circuitry in shaping somatosensory evoked scalp responses: specific changes after single-dose administration of tiagabine

OBJECTIVES

To determine whether conventional as well as high-frequency somatosensory evoked potentials (SEPs) to upper limb stimulation are influenced by GABAergic intracortical circuitry.

METHODS

We recorded SEPs from 6 healthy volunteers before and after a single-oral administration of tiagabine. Conventional low-frequency SEPs have been obtained after stimulation of the median nerve, as well as after stimulation of the first phalanx of the thumb, which selectively involves cutaneous finger inputs. Median nerve SEPs have been further analyzed after digital narrow-bandpass filtering, to selectively examine high-frequency responses. Lastly, in order to explain scalp SEP distribution before and after tiagabine administration, we performed the brain electrical source analysis (BESA) of raw data.

RESULTS

After tiagabine administration, conventional scalp SEPs showed a significant amplitude increase of parietal P24, frontal N24 and central P22 components. Similarly, BESA showed a significant strength increase of the second peak of activation of the first two perirolandic dipoles, which are likely to correspond to the N24/P24 and P22 generators. By contrast, no significant changes of high-frequency SEPs were induced by drug intake.

CONCLUSIONS

Our findings support the view that both N24/P24 and P22 SEP components are probably generated by deep spiny cell hyperpolarization, which is strongly increased by inhibitory inputs from GABAergic interneurons. By considering the clear influence of inhibitory circuitry in shaping these SEP components, conventional scalp SEP recording could be useful in the functional assessment of the somatosensory cortex in different physiological and pathological conditions. By contrast, intrinsic firing properties of the cell population generating high-frequency SEP responses are unaffected by the increase of recurrent GABAergic inhibition.

Source generators of the early somatosensory evoked potentials to tibial nerve stimulation: an intracerebral and scalp recording study

OBJECTIVE

To investigate the location of the cerebral generators of the early scalp somatosensory evoked potentials (SEPs) after tibial nerve stimulation.

METHODS

Tibial nerve SEPs were recorded in 15 patients, suffering from Parkinson's disease, who underwent implantation of intracerebral (IC) electrodes in the subthalamic nucleus, in the globus pallidum or in the thalamic ventralis intermediate nucleus. SEPs were recorded both from the scalp surface and from the IC leads.

RESULTS

The lemniscal P30 response was recorded by all the electrodes. The IC waveforms included a negative N40IC response, followed by a positive (P50IC) and a negative (N60IC) potential. The N40IC, the P50IC and the N60IC potentials did not differ in latency from the P40, the N50 and the P60 responses recorded by the Cz electrode. In 6 patients, in which SEPs were recorded also during the voluntary movement of the stimulated foot (active gating), an amplitude reduction of the SEP components following the P30 potential was observed during movement at the vertex and in the IC traces. Instead, in the contralateral temporal traces the SEP components (N40temp and P50temp) were not modified by active gating, and in the ipsilateral parietal traces only the positive potentials at about 60ms of latency was decreased.

CONCLUSIONS

Two differently oriented generators are active in the contralateral hemisphere at both 40 and 50ms of latency after tibial nerve stimulation. One source is oriented perpendicularly to the mesial hemispheric surface and generates the potentials recorded by the contralateral temporal and the ipsilateral parietal leads; the other dipolar source is radial to the hemispheric convexity, and generates the potentials at the vertex and those recorded by the IC electrodes.

Inhibition of biceps brachii muscle motor area by painful heat stimulation of the skin

ract This study aimed to evaluate whether painful cutaneous stimuli can affect specifically the excitability of the arm proximal muscle motor area. The motor evoked potentials (MEPs), recorded from the right biceps brachii muscle after either transcranial magnetic or electrical anodal stimulation of the left primary motor (MI) cortex, were conditioned by painful CO2 laser stimuli delivered either on the right hand dorsum or on the lateral surface of the right arm. Painful CO2 laser stimuli delivered on the hand skin reduced significantly the amplitude of MEPs evoked by the transcranial magnetic stimulation of the contralateral MI area, while the MEP amplitude was not significantly modified by CO2 laser pulses delivered on the arm skin. The inhibitory effect followed the arrival of the nociceptive inputs to the cerebral cortex. The amplitude of MEPs evoked by anodal electrical stimulation of the motor cortex was not decreased by conditioning painful stimuli delivered on the hand dorsum. Since the magnetic stimulation led to transynaptic activation of pyramidal neurons, while the anodal stimulation activated directly corticospinal axons, our findings suggest that CO2 laser pulses delivered on the hand are able to inhibit the arm proximal muscle motor area.

Functional changes of the primary somatosensory cortex in patients with unilateral cerebellar lesions

Although cerebellar lesions do not cause evident sensory deficits, it has been suggested recently that the cerebellum might play a role in sensory acquisition and discrimination. To determine whether the cerebellum influences the early phases of cortical somatosensory processing, we recorded cortical somatosensory evoked potentials after median nerve stimulation in five patients with unilateral cerebellar damage. We also performed a dipolar source analysis of traces by means of brain electrical source analysis. In all patients, the amplitude of the frontal N24 and parietal P24 components, as well as the strength of the corresponding dipolar sources, were significantly smaller after stimulation of the symptomatic side. These neurophysiological findings indicate that the primary somatosensory cortical processing is altered after contralateral cerebellar damage. They represent the first indication of a possible substrate for the reduction in cerebral blood flow observed in the parietal cortex after cerebellar lesion. Furthermore, the present data allow characterization of the functional influence of the cerebellar input to the primary somatosensory cortex as specifically acting over the inhibitory components of somatosensory processing.

Unmasking of an early laser evoked potential by a point localization task

OBJECTIVES

The investigation of the CO(2) laser evoked potential (LEP) modifications following a point localization task.

METHODS

LEPs were recorded from 10 healthy subjects in two different conditions. (1) Task condition: laser stimuli were shifted among 3 different locations on the right hand dorsum, and the subjects were asked to identify the stimulated area. The mean error rate in point localization was 4.5%. (2) Non-task condition: laser pulses were delivered on the first intermetacarpal space, and the subject was asked to count the number of stimuli. The mean error rate in counting was 5.8%.

RESULTS

In the task condition, the temporal traces contralateral to the stimulation showed an early positive component (eP, mean peak latency 83 ms) preceding the N1 negativity (mean peak latency 144 ms). At the eP peak latency, topographic maps showed a positivity highly focused on the contralateral temporal region. In the non-task recordings no reliable response was identifiable before the N1 potential.

CONCLUSIONS

While no LEP component earlier than the middle-latency N1 potential can be recorded in the non-task condition, a positive response (eP) preceding the N1 component is identifiable in the contralateral temporal region during the spatial localization of painful stimuli. The eP scalp distribution is compatible with its origin from a radial source in the second somatosensory (or insular) area, thus suggesting that the opercular cortex is involved not only in the middle-latency (N1 potential), but also in early pain processing.

Scalp distribution of the earliest cortical somatosensory evoked potential to tibial nerve stimulation: proposal of a new recording montage

OBJECTIVE

To investigate the most reliable method to record the earliest cortical somatosensory evoked potential (SEP) after tibial nerve stimulation. The 'gating' phenomenon was used to dissociate the overlapping cortical SEP components.

METHODS

In 11 subjects we recorded the scalp SEPs at rest, during the voluntary (active gating) and passive (passive gating) foot movement and during the isometric calf muscle contraction (isometric gating).

RESULTS

At the vertex the P40 amplitude was reduced in all the gating conditions. Instead, both the P40 response recorded in the parietal region ipsilateral to the stimulation (indicated as P40par) and the fronto-temporal N37 potential were reduced in amplitude only during the passive foot movement.

CONCLUSIONS

The same behaviour of the N37 and P40par potentials suggests that they can represent the opposite counterparts of the same dipolar generator. Instead, the real P40 amplitude, which is affected in all the gating conditions, is recorded at the vertex and might be generated by a different source. We conclude that the montage obtained by referring a temporal electrode contralateral to the stimulation to an ipsilateral parietal lead can reliably record the earliest cortical component (N37/P40par) after tibial nerve stimulation.

Somatosensory evoked potentials after multisegmental lower limb stimulation in focal lesions of the lumbosacral spinal cord

OBJECTIVES

Recording techniques permit the separate analysis of the response from cauda equina roots and the spinal potential that is probably generated by the activation of dorsal horn cells. To improve the functional assessment of focal lesions of the lumbosacral cord, lower limb somatosensory evoked potentials (SEPs) were measured by multisegmental stimulation.

METHODS

Common peroneal and tibial nerves SEPs were recorded in 14 patients in whom MRI demonstrated compressive cord damage ranging from T9 to L1 levels. SEPs were recorded in each patient at the lumbar level (cauda equina response), lower thoracic level (spinal response), and from the scalp (cortical response).

RESULTS

Abnormalities in spinal response occurred in 50% and 70% of tibial and common peroneal nerve SEPs respectively; these findings were well explained by the radiological compression level, involving in most of the patients lumbar rather than sacral myelomeres. The SEPs were often more effective than the clinical examination in showing the actual extension of damage.

CONCLUSIONS

The recording of spinal SEPs after multisegmental lower limb stimulation proved useful in assessing cord dysfunction and determining the cord levels mainly involved by the compression.

Sources of cortical responses to painful CO(2) laser skin stimulation of the hand and foot in the human brain

OBJECTIVES

To investigate whether the same dipolar model could explain the scalp CO(2) laser evoked potential (LEP) distribution after either hand or foot skin stimulation.

METHODS

LEPs were recorded in 14 healthy subjects after hand and foot skin stimulation and brain electrical source analysis of responses obtained in each individual was performed.

RESULTS

A 5 dipolar sources model explained the scalp LEP topography after both hand and foot stimulation. In particular, we showed that the co-ordinates of the two earliest activated dipoles were compatible with source locations in the upper bank of the Sylvian fissure on both sides. These sources did not change their location when the stimulation site was moved from the upper to the lower limb. The other 3 dipoles of our model were activated in the late LEP latency range with a biphasic profile and a location compatible with activation of the cingulate gyrus and deep temporo-insular structures.

CONCLUSIONS

The dipolar model previously proposed for the hand stimulation LEPs can also satisfactorily explain the LEP distribution obtained after foot stimulation. The earliest activated Sylvian dipolar sources did not change their location when the upper or lower limb was stimulated, as expected from the close projections of hand and foot in the second somatosensory area. No source in the primary somatosensory area was necessary to model the scalp topography of LEPs to hand and foot stimulation.

Anatomic origin of P13 and P14 scalp far-field potentials

After median nerve stimulation, noncephalic or earlobe reference montages enable one to record over the scalp a well-defined, positive far-field response, which has been labeled the P14 or P13-P14 complex. It has been ascertained that this wave is generated in the caudal brainstem. Its use is reliable and sometimes mandatory in assessing a number of diseases that affect primarily the brainstem, such as multiple sclerosis or coma. Because of its complex shape as well as discrepant findings in the literature, it is still debated whether this potential is produced by a single or by multiple serial generators. The authors present these different views and summarize the different recording methods, while bearing in mind that some recording techniques are more suitable for routine purposes and others are preferred in selected cases, when more information regarding caudal brainstem function is required.

Central scalp projection of the N30 SEP source activity after median nerve stimulation

Conflicting results have been reported about abnormalities of the N30 somatosensory evoked potential (SEP) in movement disorders. In these studies, the N30 amplitude was measured in the frontal scalp region. Our aim was to identify the scalp electrodes recording the genuine activity of the N30 generator. In 18 subjects, we recorded the scalp SEPs from 19 electrodes and found a negative potential around 30 ms reaching its maximal amplitude in the frontal region. However, neither simple visual inspection of the frontal traces nor topographic analysis could distinguish the N24 from the N30 component of the frontal negativity. Brain electrical source analysis of SEPs showed that a four dipolar source model could well explain the scalp SEP distribution. We calculated the scalp field distributions of the source activities as modeled from the scalp recordings and observed that the maximal field distribution reflecting the activity of the N30 source was in the central region, whereas that reflecting the N24 source activity was frontal. We conclude that the negative response recorded around 30 ms in the central traces represents "genuine" N30 source activity, whereas the frontal negativity, which is higher in amplitude, is a mixture of the activities of both the N30 and N24 sources.

Open-door laminoplasty for cervical stenotic myelopathy: surgical technique and neurophysiological monitoring

OBJECT

A modified technique of open-door laminoplasty for cervical stenotic myelopathy (CSM) is described, and the role of evoked potential monitoring in selecting patients for surgery and evaluating results is discussed.

METHODS

Between October 1992 and October 1996, 33 patients with CSM underwent open-door laminoplasty. After surgery, in 27 patients (81.8%) different levels of clinical improvement were demonstrated, and in five of them (15%) full recovery was observed. The Japanese Orthopaedic Association score increased from 5 to 12 (mean 9.8) preoperatively to 8 to 14 (mean 11.6) postoperatively. At 1-year follow up, the N13 cervical response was restored in nine (75%) of 12 patients with isolated presurgical abnormality and in 57.1% of those with combined abnormalities of both N13 and P14 response. Although significant clinical improvement was observed in 82% of the cases, in 24 of 33 patients motor evoked potential abnormalities persisted at least at one explored level.

CONCLUSIONS

Of several laminoplasty techniques, the one described here offers some advantages: preservation of biomechanical function of posterior muscular-ligamentous complex, prevention of laminar collapse, smaller degrees in reduction of range of cervical motion, stabilization of the spine with no postoperative malalignment, and maintenance of decompressive effect that avoids recurrent stenosis. Neurophysiological studies sometimes clarified neurological disorders that were only suspected on the basis of history and/or clinical examination, leading to early diagnosis.

Effect of movement on dipolar source activities of somatosensory evoked potentials

The early scalp somatosensory evoked potentials (SEPs) to median and tibial nerve stimulation were recorded at rest and during voluntary movement of the stimulated hand and foot, respectively. Both tibial and median nerve SEP distributions at rest could be explained by four-dipole models, in which one dipole was activated at the same latency as the subcortical far field and the three remaining dipolar sources were located in the perirolandic region contralateral to the stimulated side. Voluntary movement reduced all cortical dipoles in strength, while the subcortical one remained unchanged, suggesting that the effect of movement occurs above the cervicomedullary junction. In animals, cutaneous inputs are suppressed during movement and we therefore interpreted the depression of activity in the primary somatosensory cortex induced by movement as due to selective "gating" of cutaneous afferents. Because the reduction in strength of the cortical dipoles was generally lower during passive than active movement, both centrifugal and centripetal mechanisms probably contribute to the phenomenon of "gating."

Inhibition of the human primary motor area by painful heat stimulation of the skin

OBJECTIVE

To prove whether painful cutaneous stimuli can affect specifically the motor cortex excitability.

METHODS

The electromyographic (EMG) responses, recorded from the first dorsal interosseous muscle after either transcranial magnetic or electric anodal stimulation of the primary motor (MI) cortex, was conditioned by both painful and non-painful CO2 laser stimuli delivered on the hand skin.

RESULTS

Painful CO2 laser stimuli reduced the amplitude of the EMG responses evoked by the transcranial magnetic stimulation of both the contralateral and ipsilateral MI areas. This inhibitory effect followed the arrival of the nociceptive inputs to cerebral cortex. Instead, the EMG response amplitude was not significantly modified either when it was evoked by the motor cortex anodal stimulation or when non-painful CO2 laser pulses were used as conditioning stimuli.

CONCLUSIONS

Since the magnetic stimulation leads to transynaptic activation of pyramidal neurons, while the anodal stimulation activates directly cortico-spinal axons, the differential effect of the noxious stimuli on the EMG responses evoked by the two motor cortex stimulation techniques suggests that the observed inhibitory effect has a cortical origin. The bilateral cortical representation of pain explains why the painful CO2 laser stimuli showed a conditioning effect on MI area of both hemispheres. Non-painful CO2 laser pulses did not produce any effect, thus suggesting that the reduction of the MI excitability was specifically due to the activation of nociceptive afferents.

Different contribution of joint and cutaneous inputs to early scalp somatosensory evoked potentials

To elucidate whether the frontal components of scalp somatosensory evoked potentials (SEPs) depend on the type of peripheral input, we compared scalp SEPs in response to electrical stimuli applied to: (i) the proximal phalanx of the thumb, involving both deep and cutaneous afferents; and (ii) the distal phalanx of the thumb, involving cutaneous afferents, but excluding joint inputs coming from the interphalangeal articulation. We applied the same dipolar model that we built to explain the scalp SEP distribution to median nerve stimulation in previous investigations. Cortical SEPs after proximal stimulation were generated by three dipolar sources, one of which was likely to account for the frontal scalp N30. When we analyzed SEPs for distal (purely cutaneous) stimulation, the frontal and central recordings showed a clear reduction in amplitude of the negative responses having a latency of about 30 ms. Moreover, when applying the dipole model derived from analysis of responses to proximal stimulation to SEPs to distal stimulation, the source corresponding to the N30 distribution showed no activity, suggesting a strong relationship between joint and tendinous inputs and the activity of the N30 generator.

Clinical and neurophysiological abnormalities before and after reconstruction of the anterior cruciate ligament of the knee

OBJECTIVES

We aimed to study knee proprioception and somatosensory evoked potentials (SEPs) to stimulation of the common peroneal nerve (CPN) in 7 patients with lesion of the anterior cruciate ligament (ACL) before and after ACL reconstruction.

MATERIALS AND METHODS

We recorded the spinal N14 and scalp P27 potentials in 5 patients, while in the remaining 2 patients we calculated scalp SEP maps by 20 electrodes. The knee proprioception was tested by comparing the sensitivity to movement of both the knees.

RESULTS

Before surgery, all patients showed decreased knee position sense and lack of the cortical P27 potential on the side of the ACL lesion. Arthroscopic reconstruction of the ligament improved neither the knee proprioception nor the somatosensory central conduction.

CONCLUSION

We suggest that the loss of the knee mechanoreceptors can be followed by modifications of the central nervous system, which are not compensated by other nervous structures.

Neurophysiologic follow-up of long-term dietary treatment in adult-onset adrenoleukodystrophy

OBJECTIVE

To monitor the effects of dietary treatment in adult-onset adrenoleukodystrophy (ALD) by means of somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs).

BACKGROUND

SEPs and MEPs have proved useful in revealing signs of progressively severe, central dying-back axonopathy in early stages of adult-onset ALD.

METHODS

Eight patients with adult-onset ALD underwent clinical examination, brain and spine MRI, and SEP and MEP studies before and after 3 years of Lorenzo's oil dietary therapy.

RESULTS

Before treatment, brain MRI was normal in five patients. Three of these patients had pure spinal SEP abnormalities and in the remaining two patients SEPs showed signs of involvement of both the spinal and cerebral somatosensory tracts. After treatment, the three patients with pure spinal abnormalities showed clinical and neurophysiologic worsening, whereas the two patients with a more advanced stage of disease (exhibited by SEPs) showed substantially unchanged clinical and neurophysiologic features. The patients with abnormal brain MRI at the onset of treatment showed clinical and neurophysiologic worsening.

CONCLUSIONS

Lorenzo's oil therapy had no effect on patients with evidence of inflammatory brain lesions. Moreover, in patients without clear signs of inflammatory damage, this treatment does not modify significantly the natural course of the disease. However, because effective treatments should begin before the onset of severe neurologic symptoms, SEPs and MEPs should be considered to evaluate the effectiveness of other experimental treatments in the patient with a negative brain MRI.

Anterior cervical epidural abscess treated by endoscopy-assisted minimally invasive microsurgery via posterior approach

This is a report of clinical manifestation, physical findings, neurophysiological data, magnetic resonance imaging, and results after surgery in a 71-years-old man with cervical abscess. Magnetic resonance imaging after two weeks of empiric antibiotic therapy demonstrated the persistence of an anterior cervical epidural collection and signs of spondylodiscitis at the C5-C6 and C6-C7 levels. Surgery was performed by posterior endoscopy assisted key-hole approach at the C2-C3 level to drain the abscess and to decompress the spinal cord. Postoperative specific medical treatment was then administered. A successful outcome, at 24 months follow-up, was achieved by surgery with complete clinical recovery, resolution of the abscess and healing of the spondylodiscitis. After unsuccessful blind medical therapy the minimally invasive microsurgical technique allowed us to keep the surgical injury of the healthy tissue to a minimum while producing the maximum therapeutic effect.

The scalp to earlobe montage as standard in routine SEP recording. Comparison with the non-cephalic reference in patients with lesions of the upper cervical cord

We compared scalp somatosensory evoked potential (SEP) recordings by non-cephalic and earlobe reference in 14 healthy subjects and in 5 patients with lesions of the upper cervical cord. In healthy subjects, the scalp to earlobe montage tended to cancel all far-field potentials preceding the scalp P14. On the contrary, the P14 far-field was more difficult to identify in scalp to non-cephalic recordings, because in 12/14 cases it followed another far-field (P13), which was very close in latency to the P14. In 4 patients, the scalp to non-cephalic traces showed a single positive wave (P13/P14 complex) in the P14 latency range. If this complex had been labelled as P14, the somatosensory dysfunction would have been localised above the foramen magnum. On the other hand, the scalp to earlobe recording allowed correct localisation of the lesion since it showed the 'real' and delayed P14 in two patients and no far-field response in the remaining two. Therefore, we propose the use of the scalp to earlobe montage as standard in routine examinations.

Selective abnormality of the N13 spinal SEP to dermatomal stimulation in patients with cervical monoradiculopathy

Scalp somatosensory evoked potentials (SEP) to dermatomal stimulation have so far proved to be only partially useful in the diagnosis of monoradiculopathy, mostly in cases without motor impairment. The aim of our study was to test the sensitivity of the spinal N13 potential in uncovering lesions of single cervical roots. We studied five patients suffering from cervical monoradiculopathy, using a recording technique allowing specific recording of the genuine N13 potential which is probably generated by dorsal horn cells. No patient showed signs of muscle impairment and needle EMG was always normal. In four patients, the N13 SEP was absent following stimulation of the dermatome corresponding to the damaged root, while both the lemniscal P14 and the cortical N20 components were normal. SEP recorded after stimulation of upper limb troncular nerves showed no abnormality in all patients. Our findings suggest that the N13 potential, the loss of which after dermatomal stimulation could be due to deafferentation of dorsal horn neurones, is particularly sensitive to initial root compression. Therefore, our montage allowing analysis of the genuine N13 SEP can improve the sensitivity of dermatomal SEP recording in patients with cervical monoradiculopathies.

Dipolar sources of the early scalp somatosensory evoked potentials to upper limb stimulation. Effect of increasing stimulus rates

Brain electrical source analysis (BESA) of the scalp electroencephalographic activity is well adapted to distinguish neighbouring cerebral generators precisely. Therefore, we performed dipolar source modelling in scalp medium nerve somatosensory evoked potentials (SEPs) recorded at 1.5-Hz stimulation rate, where all the early components should be identifiable. We built a four-dipole model, which was issued from the grand average, and applied it also to recordings from single individuals. Our model included a dipole at the base of the skull and three other perirolandic dipoles. The first of the latter dipoles was tangentially oriented and was active at the same latencies as the N20/P20 potential and, with opposite polarity, the P24/N24 response. The second perirolandic dipole showed an initial peak of activity slightly earlier than that of the N20/P20 dipolar source and, later, it was active at the same latency as the central P22 potential. Lastly, the third perirolandic dipole explaining the fronto-central N30 potential scalp distribution was constantly more posterior than the first one. In order to evaluate the effect of an increasing repetition frequency on the activity of SEP dipolar sources, we applied the model built from 1.5-Hz SEPs to traces recorded at 3-Hz and 10-Hz repetition rates. We found that the 10-Hz stimulus frequency reduced selectively the later of the two activity phases of the first perirolandic dipole. The decrement in strength of this dipolar source can be explained if we assume that: (a) the later activity of the first perirolandic dipole can represent the inhibitory phase of a "primary response"; (b) two different clusters of cells generate the opposite activities of the tangential perirolandic dipole. An additional finding in our model was that two different perirolandic dipoles contribute to the centro-parietal N20 potential generation.

Functional involvement of cerebral cortex in Duchenne muscular dystrophy

Transcranial stimulation was performed in 4 patients with Duchenne muscular dystrophy and 4 control subjects. The patients' central motor conduction time was normal. The threshold for evoking electromyographic responses using electrical anodal stimulation was the same in both groups, but the threshold for stimulation with a circular magnetic coil at the vertex was higher in the patients. This is compatible with reduced cortical excitability that may be related to the deficiency of brain synaptic dystrophin.

Effects of voluntary contraction on descending volleys evoked by transcranial stimulation in conscious humans

1. The spinal volleys evoked by single transcranial magnetic or electric stimulation over the cerebral motor cortex were recorded from a bipolar electrode inserted into the cervical epidural space of three conscious human subjects. These volleys were termed direct (D) and indirect (I) waves according to their latency. 2. We measured the size and number of volleys elicited by magnetic stimulation at various intensities with subjects at rest and during 20 or 100 % maximum contraction of the contralateral first dorsal interosseous muscle (FDI). Surface EMG activity was also recorded. 3. Electrical stimulation evoked a D-wave volley. Magnetic stimulation at intensities up to about 15 % of stimulator output above threshold evoked only I-waves. At higher intensities, a D-wave could be seen in two of the three subjects. 4. At all intensities tested, voluntary contraction increased the number and size of the I-waves, particularly during maximum contractions. However, there was only a small effect on the threshold for evoking descending activity. Voluntary contraction produced large changes in the size of EMG responses recorded from FDI. 5. Because the recorded epidural activity is destined for muscles other than the FDI, it is impossible to say to what extent increased activity contributes to voluntary facilitation of EMG responses. Indeed, our results suggest that the main factor responsible for enhancing EMG responses in the transition from rest to activity is likely to be increased excitability of spinal motoneurones, rather than increases in the corticospinal volley. The latter may be more important in producing EMG facilitation at different levels of voluntary contraction.

Dissociation induced by voluntary movement between two different components of the centro-parietal P40 SEP to tibial nerve stimulation

Whether the two earliest cortical somatosensory evoked potentials (SEPs) to tibial nerve stimulation (N37 and P40) are generated by the same dipolar source or, instead, originate from different neuronal populations is still a debated problem. We recorded the early scalp SEPs to tibial nerve stimulation in 10 healthy subjects at rest and during voluntary movement of the stimulated foot. We found that the P40, which reached its highest amplitude on the vertex at rest, changed its topography during movement, since its amplitude was reduced much more in the central than in the parietal traces. These findings suggest that two different components contribute to the centro-parietal positivity at rest: (1) the P37 response, which is parietally distributed and is not modified by movement, and (2) the 'real' P40 SEP, which is focused on the vertex and is reduced in amplitude during voluntary movement. Since, also, the N37 response did not vary its amplitude under interference condition, it is possible that the N37 and P37 potentials are generated by the same dipolar source. Other later components, namely P50 and N50 were significantly reduced in amplitude during foot movement. Lastly, the subcortical P30 far-field remained unchanged and this suggests that the phenomenon of amplitude reduction during movement (i.e. gating) occurs above the cervico-medullary junction.

Magnetic transcranial stimulation at intensities below active motor threshold activates intracortical inhibitory circuits

A magnetic transcranial conditioning stimulus given over the motor cortex at intensities below threshold for obtaining electromyographical (EMG) responses in active hand muscles can suppress responses evoked in the same muscles at rest by a suprathreshold magnetic test stimulus given 1-5 ms later. In order to define the mechanism of this inhibitory effect, we recorded descending volleys produced by single and paired magnetic transcranial stimulation of motor cortex through high cervical, epidural electrodes implanted for pain relief in two conscious subjects with no abnormality of the central nervous system. The conditioning stimulus evoked no recognisable descending activity in the spinal cord, whilst the test stimulus evoked 3-4 waves of activity (I-waves). Conditioning stimulation suppressed the size of both the descending spinal cord volleys and the EMG responses evoked by the test stimulus. Inhibition of the descending spinal volleys was most pronounced at ISI 1 ms and had disappeared by ISI 5 ms. It was evident for all components following the I1-wave, while the I1-wave itself was not inhibited at all. We conclude that a small conditioning magnetic stimulus can suppress the excitability of human motor cortex, probably by activating local corticocortical inhibitory circuits.

Dipolar generators of the early scalp somatosensory evoked potentials to tibial nerve stimulation in human subjects

We performed the brain electrical source analysis (BESA) of the early scalp somatosensory evoked potentials (SEPs) to tibial nerve stimulation. A four-dipole model could well explain the scalp SEP distribution. One dipole showing a subcortical location was activated at the latency of the lemniscal P30. The three remaining dipoles were located near the sagittal fissure in the hemisphere contralateral to the stimulation. Two of these dipoles showed a biphasic activity and contributed to the signal evoked in the N37-P40 latency range. Also in the N50-P50 latency range two different source activities were involved in SEP building. This finding suggests that one of two possible N50 subcomponents represents the negative counterpart of the N50/P50 dipolar field and the other is originated by a radial source.

Abnormalities of somatosensory and motor evoked potentials in adrenomyeloneuropathy: comparison with magnetic resonance imaging and clinical findings

We studied 6 patients with adrenomyeloneuropathy (AMN) showing mild signs of central nervous system involvement. All patients underwent brain and spinal magnetic resonance imaging (MRI) and somatosensory (SEP) and motor (MEP) evoked potential study. Whereas SEPs and MEPs were abnormal in all patients, only 1 patient showed brain MRI abnormalities; spinal MRI showed hypotrophy without focal abnormalities in 4 of 6 patients. Median nerve SEPs, which were recorded with noncephalic reference montage, revealed delayed or absent scalp P14 far-field potential in all patients and abnormal spinal N13 in 2. Moreover, tibial nerve SEPs revealed abnormalities of the subcortical P30 response in all 4 patients in whom scalp-to-ear recording was employed. These findings strongly suggest that in the early stages of disease neurological dysfunction is localized in the spinal cord, where it is difficult to assess using MRI. However, SEPs and MEPs, which show a typical pattern of abnormality in these patients, could be useful in disclosing signs of long tract involvement and in monitoring treatment.

Ischaemic myelopathy associated with cocaine: clinical, neurophysiological, and neuroradiological features

Two patients with spinal infarction and one patient with the previously unreported complication of spinal transient ischaemic attack associated with cocaine misuse are reported. Spinal MRI documented an infarction in the territory of the anterior spinal artery in the first two patients and was completely normal in the patient with a transient ischaemic attack. Motor evoked potentials were abnormal in all three patients.

Neurophysiological abnormalities in adrenoleukodystrophy carriers. Evidence of different degrees of central nervous system involvement

We studied 19 women, heterozygous for adrenoleukodystrophy (ALD) in whom the carrier status was demonstrated by abnormally high plasma levels of very-long-chain fatty acids. Clinical examination revealed slight neurological signs in two patients. Clear-cut neurological deficits in three, and it was fully normal in the remaining 14. All subjects underwent motor evoked potential (MEP) and somatosensory evoked potential (SEP) studies. Seventeen out of 19 subjects underwent brain MRI which demonstrated various degrees of abnormality in one asymptomatic and five symptomatic subjects; SEPs and MEPs revealed CNS involvement in 12 and 8 out of the 19 subjects, respectively. Symptomatic patients showed severe neurophysiological abnormalities, whereas milder but unequivocal EP abnormalities were found in seven of the 14 patients with normal clinical examination. Our data thus suggest CNS involvement in the majority of the ALD carriers, evident also in preclinical stages and progressively severe. The possibility of assessing different degrees of neurological involvement could be relevant for therapeutical purposes. Moreover, neurophysiological studies could provide the only objective marker of functional nervous system involvement, e.g. in order to monitor the efficacy of treatment, and in clinically and radiologically silent cases.

Functional involvement of central nervous system in mitochondrial disorders

Thirty-nine patients with mitochondrial diseases were studied with somatosensory and motor evoked potentials. Sixteen patients (41%) had clinical and 12 (31%) had neuroradiological evidence of central nervous system involvement. The overall incidence of electrophysiological abnormalities was 64%. Abnormal evoked potentials were also found in a significant percentage (33%) of patients with pure myopathic forms of mitochondrial diseases and in an asymptomatic carrier of MERRF mutation. Of the individual tests, somatosensory evoked potentials were abnormal in 49% of the patients and motor evoked potentials were abnormal in 46% of the patients. The outcome is that electrophysiological evidence of central nervous system involvement is present in a high percentage of patients with mitochondrial disorders, and that the threshold for central nervous system electrophysiological abnormalities is well below that for clinical and/or radiological manifestations.

The pathophysiology of giant SEPs in cortical myoclonus: a scalp topography and dipolar source modelling study

Somatosensory evoked potential (SEP) recordings in patients suffering from cortical myoclonus (CM) are characterised by evidence of abnormally enhanced scalp components. Our aim was to verify whether enhanced activity in giant SEPs arises from the same generators as in healthy subjects. We used the brain electrical source analysis (BESA) to compare scalp SEP generators of healthy subjects to those calculated in 3 patients with CM of varying causes. Firstly, we built a 4-dipole model explaining scalp distribution of early SEPs in normal subjects and then applied it to traces recorded from CM patients. Our model, issued from the right median nerve grand average and applied also to recordings from single individuals, included a dipole at the base of the skull and three other perirolandic dipoles. The first of the latter dipoles was tangentially oriented and was active at the same latencies as the N20/P20 potentials and, with opposite polarity, the P24/ N24 responses; the second dipole explained the central P22 distribution and the third had a peak of activity corresponding to the N30 component. When we applied our 4-dipole model to CM recordings, the first perirolandic dipole had a third peak of activity in all patients at the same latency as a parietal negativity and a frontal positivity, both following giant P24/N24 components; on the other hand, in one patient the second perirolandic dipole showed a later activation corresponding to a high central negativity, following a giant P22 response. We suggest that only the initial giant SEPs correspond to physiological potentials evoked in healthy subjects. The occurrence of late giant SEPs could be explained by hyperpolarization, following the postsynaptic excitatory potentials responsible for the early giant components.

Giant central N20-P22 with normal area 3b N20-P20: an argument in favour of an area 3a generator of early median nerve cortical SEPs?

Generators of early cortical somatosensory evoked potentials (SEPs) still remain to be precisely localised. This gap in knowledge has often resulted in unclear and contrasting SEPs localisation in patients with focal hemispheric lesions. We recorded SEPs to median nerve stimulation in a patient with right frontal astrocytoma, using a 19-channel recording technique. After stimulation of the left median nerve, N20 amplitude was normal when recorded by the parietal electrode contralateral to the stimulation, while it was abnormally enhanced in traces obtained by the contralateral central electrode. The amplitude of the frontal P20 response was within normal limits. This finding suggests that two dipolar sources, tangential and radial to the scalp surface, respectively, contribute concomitantly to N20 generation. The possible location of the N20 radial source in area 3a is discussed. The P22 potential was also recorded with increased amplitude by the central electrode contralateral to the stimulation, while N30 amplitude was normal in frontal and central traces. We propose that the radial dipolar source of P22 response is independent from both N20 and N30 generators and can be located either in 3a or in area 4. This report illustrates the usefulness of multichannel recordings in diagnosing dysfunction of the sensorimotor cortex in focal cortical lesions.

Changes in spinal cord excitability in a patient with rhythmic segmental myoclonus

Paired stimulation of the common peroneal and posterior tibial nerve was used to study the recovery cycle of lumbosacral somatosensory evoked potentials in 10 control subjects and in one patient with rhythmic segmental myoclonus of the leg involving the L2-L4 myotomes. In normal subjects the peripheral nerve volley in the cauda equina had recovered at an interstimulus interval of 3 ms whereas the postsynaptic dorsal horn potential was reduced to about 60% of its control size. Similar results were found in the patient after posterior tibial nerve but not common peroneal nerve stimulation. The second, which evokes afferent input to the affected lumbar segments, produced facilitation of the postsynaptic response at 3 ms. This finding suggests that the physiological suppression of dorsal horn interneurons which usually takes place after paired stimulation fails to occur in segmental myoclonus. This may indicate that dorsal horn interneurons are abnormally hyperactive and are involved in the pathophysiology of spinal myoclonus.