Generalisability of sensory gating during passive movement of the legs

Movement-related gating of somatosensory evoked potentials in the upper limb is restricted mainly to nerve stimulation supplying the moved limb segment. In the lower limb, this principle may not be followed. Tibial nerve (stimulation at the knee) somatosensory evoked potentials (SEPs) and soleus H reflexes exhibit quite similar patterns of modulation during movement. We hypothesised that movement-related gating of initial SEPs in the leg would be generalised from ipsilateral to contralateral leg movement and that such sensory gating would not be generalised to modalities with no functional relevance to the movement. Somatosensory, visual, and auditory evoked potentials (SEPs, VEPs, and AEPs) were recorded from scalp electrodes during unilateral passive movement. Short-latency tibial nerve SEPs, representing the first cortical components, and soleus H reflexes in both the moved leg and the stationary leg were attenuated compared to non-movement controls (p<0.05). Neither VEPs nor middle latency AEPs were modulated (p>0.05). We conclude that sensory gating occurs during contralateral movement. This gating is absent in other sensory modalities with no apparent functional relationship to the imposed movement.     

Assessing the role of the biomaterial Aquavene in patient reactions to Landmark midline catheters

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.     

Facilitation of somatosensory evoked potentials by exploratory finger movements

Modification of somatosensory processing depending on the behavioral setting was studied. Active alternating movements of the fingers, passive tactile stimuli to the hand, and active exploration of objects were performed during recording of somatosensory evoked potentials (SEPs). SEPs were elicited by compound electrical median nerve stimulation and electrical stimulation at detection threshold of cutaneous median nerve fascicles identified by microneurography. Electrical stimulation was not time-locked to the studied condition. In comparison with SEPs at rest there was attenuation of early cortical potentials up to 25 ms post-trigger in all nonresting conditions. In stimulation of the compound median nerve as well as of isolated cutaneous fascicles of a hand actively exploring an object there was an additional increased negativity, peaking at 28 ms. This facilitory effect was independent of attentional focusing and was absent during exploration using the ipsilateral, non-electrically stimulated hand. In patients with parietal lesions the facilitatory effect was diminished on the affected side. Spline interpolated brain maps at this latency based on 32-channel recordings in healthy volunteers showed a shift of local contralateral positive maximum from frontal to parietal during exploration, indicating enhancement of a tangential dipole. It is suggested that in conditions involving close sensorimotor interaction such as exploratory hand movements there is preactivation of a cortical area which is located in the central sulcus and receives cutaneous somatosensory inputs.     

Crossed and direct effects of digital nerves stimulation on motor evoked potential: a study with magnetic brain stimulation

We studied the influence of contralateral and ipsilateral cutaneous digital nerve stimulation on motor evoked potentials (MEPs) elicited in hand muscles by transcranial magnetic stimulation (TMS). We tested the effect of different magnetic stimulus intensities on MEPs recorded from the thenar eminence (TE) muscles of the right hand while an electrical conditioning stimulus was delivered to the second finger of the same hand with an intensity four times above the sensory threshold. Amplitude decrement of conditioned MEPs as a function of magnetic stimulus intensity was observed. The lowest TMS stimulus intensity produced the largest decrease in conditioned MEPs. Moreover, we investigated the effects of ipsilateral and contralateral electrical digital stimulation on MEPs elicited in the right TE and biceps muscle using an intensity 10% above the threshold. Marked MEP inhibition in TE muscles following both ipsilateral and contralateral digital stimulation is the main finding of this study. The decrease in conditioned MEP amplitude to ipsilateral stimulation reached a level of 50% of unconditioned MEP amplitude with the circular coil and 30% with the focal coil. The amplitude of conditioned MEPs to contralateral digital stimulation showed a decrease of 60% with the circular coil and more than 50% with the focal coil. The onset of the inhibitory effect of contralateral stimulation using the focal coil occurred at a mean of 15 ms later than that of ipsilateral stimulation. No MEP inhibition was observed when recording from proximal muscles. Ipsilateral and contralateral digital stimulation had no effect on F wave at appropriate interstimulus intervals, where the main MEP suppression was noted. We stress the importance of selecting an appropriate test stimulus intensity to evaluate MEP inhibition by digital nerves stimulation. Spinal and cortical sites of sensorimotor integration are adduced to explain the direct and crossed MEP inhibition following digital nerves stimulation.     

Effects of stimulus intensity on signals from human somatosensory cortices

We recorded somatosensory evoked magnetic fields (SEFs) to left median nerve electric stimulation from seven healthy subjects. The stimulus intensity was varied in three sessions: sensory stimuli evoked a clear tactile sensation without any movement, weak motor stimuli exceeded the motor threshold, and strong motor stimuli caused a vigorous movement. Responses were modelled with sources in the contralateral primary somatosensory cortex (SI), the contralateral and ipsilateral secondary somatosensory cortices (SIIs) and the contralateral posterior parietal cortex (PPC). The amplitude of the 20 ms response from the SI cortex and the subjective magnitude estimations followed the stimulus intensity whereas signals from the three other areas saturated already at the level of the motor threshold. The results implicate differential roles for various somatosensory cortices in intensity coding.     

Neurotransmitter background of the anti-inflammatory effect evoked by activation of sensory nerve fibers

Intra-operative cortical and subcortical SEPs from the cerebral convexity and from the inter-hemispheric fissure were recorded following posterior tibial nerve (PTN) stimulation. Cortical and subcortical SEPs from the cerebral convexity after contra-lateral PTN stimulation consisted of N38 and P46, and their polarity reversed when the ipsi-lateral site was stimulated. On the other hand, cortical SEPs from the inter-hemispheric fissure always showed P38 and N46, whether the right or the left PTN was stimulated. Cortical and subcortical SEPs from the inter-hemispheric fissure showed clear cut polarity reversals. These findings provide good evidence for the existence of a tangential dipole oriented perpendicular to the inter-hemispheric fissure in the foot sensory area of the primary sensory cortex. SEPs recorded from the superficial part of the inter-hemispheric fissure showed smaller amplitudes and longer latencies than those of SEPs from the deeper regions. These findings suggest the existence of another dipole responsible for the generation of SEPs after PTN stimulation.     

Neoadjuvant chemotherapy for extremity osteosarcoma--preliminary results of the Rizzoli''s 4th study

OBJECTIVES: Our study was designed to clarify the role of the thalamus in the generation of the electrically elicited long-latency reflexes (LLR) in voluntarily activated hand muscles. MATERIALS AND METHODS: EMG responses of the thenar muscles were evoked by electrical stimulation of the median nerve at the wrist at motor threshold intensity in 10 patients with acute pure sensory stroke due to thalamic infarction. Concomitant recording of somatosensory evoked potentials (SEPs) was performed. The subjects were asked to steadily abduct the thumb at 20-30% of maximal force against a force transducer. Rectified and averaged EMG activities were recorded. RESULTS: The LLR II was missing completely or significantly attenuated in the majority of the patients (9 of 10), of whom 3 also had delayed latency. Abnormal SEPs were documented in 7 patients (7 of 10). In the follow-up, 5 patients had partial reversal of LLR II. LLR II was still pathological in 1 fully recovered patient. CONCLUSION: Our results further confirm the transcortical generation of LLR II and imply that a thalamic relay is present in the afferent limb of the LLR.     

Abnormal sensory nerve conduction in multifocal demyelinating neuropathy with persistent conduction block

Two patients exhibited chronic, slightly asymmetric weakness and wasting with fasciculations of the upper limb and hand muscles. Motor nerve conduction studies showed features of multifocal conduction block in nerve segments other than those usually involved in entrapment syndromes. The F wave was markedly delayed in the median and ulnar nerves. Transcranial cortical and cervical root magnetic stimulation showed bilaterally delayed thenar responses with normal central conduction time. Needle electromyography demonstrated a chronic denervation pattern with large polyphasic motor units in several muscles of the upper limbs. Sensory symptoms were mild and limited to paresthesias in the fingertips. Sensory nerve conduction velocity and sensory nerve action potential amplitudes were normal in elbow-to-wrist and wrist-to-finger segments of the median and ulnar nerves, but there was a delayed cortical response and unrecognizable Erb's point and cervical responses in the somatosensory evoked potentials to median nerve electrical stimulation. Electrophysiologic examination was normal in most nerves of the lower limbs. These two patients, meeting clinical and electrophysiologic criteria of multifocal neuropathy with conduction block, demonstrate that sensory fibers may also be involved in this syndrome.     

NF-kappaB2 is a putative target gene of activated Notch-1 via RBP-Jkappa

Cutaneous stimulation of the face and hand with a CO2 laser in three awake patients evoked potentials (LEPs) recorded from the dominant left parasylvian cortex. These were recorded by means of a subdural grid of electrodes implanted for evaluation of epilepsy. Stimulation of the contralateral face resulted in waveforms consisting of a negative potential (N2, 162 +/- 5 ms; mean +/- SE) followed by a positive potential (P2, 340 +/- 18 ms). Both waves occurred at longer latency after hand than after facial stimulation. N2 and P2 potentials recorded from the grid correspond well in morphology to those recorded from the scalp in four additional patients tested with the same stimulation paradigm. The N2 waves recorded from the subdural grid occurred at significantly shorter latencies than did those recorded from the scalp (184 +/- 6 ms), but the P2 waves at the grid occurred at significantly longer latencies than did those recorded at the scalp (281 +/- 13 ms). The amplitudes of the potentials recorded from the grid were maximal over the parietal operculum both for contralateral stimulation of the face or hand and for ipsilateral stimulation of the face. Potentials also were recorded in this area after stimulation of the ipsilateral hand. The cortical distributions of these potentials suggest that their generators are located in the parietal operculum or in the insula, or in both, consistent with previous PET, magnetoencephalographic, and scalp LEP source analyses. These previous analyses provide indirect evidence of nociceptive input to parasylvian cortex because the interpretation of each analysis incorporates multiple assumptions. The present results are the first direct evidence of nociceptive input to the human parasylvian cortex.     

Isochronic mapping of the auditory brainstem response: normative results

Isochronic mapping involves recording multi-channel evoked potentials from scalp electrodes and plotting contours of peak latencies. In this study, auditory brainstem responses were recorded from 20 electrode sites for left, right and binaural stimulation of each ear of 10 male and 10 female, normally hearing, young adults. Analysis of the data showed that the stimulus parameters of intensity, polarity and rate had no significant effect on the maps. On monaural stimulation, wave V was recorded first at the contralateral mastoid and ipsilaterally frontally and last at the ipsilateral mastoid some 350, mu s later. Binaural stimulation gave a symmetrical map, with wave V recorded first frontally and last at the occiput. In contrast, wave III was recorded first ipsilaterally and frontally and last at the contralateral mastoid. Wave II was recorded first at the rear of the contralateral mastoid and last forward of the ipsilateral mastoid. Comparisons between these results and human physiological studies are in agreement for waves V and III but do not support the concept of the VIIth nerve alone as the generator for wave II. These results suggest that this technique is a potentially useful diagnostic tool and it is intended to evaluate it by testing patients with a range of sensory, peripheral-neural and central-neural pathologies.     

Giant somatosensory evoked potentials in a patient with the anterior spinal artery syndrome

We studied a previously healthy 25-year-old woman with the anterior spinal artery syndrome, a rare thoracocervical myelopathy with multiple potential etiologies. Quantitative and clinical sensory examination showed dissociated loss of pin-prick and temperature discrimination below the level of the lesion, with normal light touch, vibratory, and position sense. Magnetic resonance imaging was consistent with cervical spinal cord infarction. Median SEPs showed normal Erb's potential with absent spinal N13- and normal scalp N20- latency. Tibial SEPs showed normal lumbosacral responses and normal scalp P30- latency. Both median and tibial nerve stimulation produced cortical responses of unusually large amplitude (median 38 microV, tibial 17 microV). We hypothesize that large SEP amplitudes in this patient resulted from loss of anterolateral inhibitory influences on the dorsal column-medial lemniscal system.     

The clinical link between migraine and cluster headaches

We describe seven patients with vascular headaches. Five of them had cluster headaches, which were preceded by migrainous scotamata (two patients), weakness contralateral to the pain (one), accompanied by ipsilateral photopsias (one), or by contralateral paresthesias (one). The other two patients had "clusters" of daily common migraine headaches separated by long free intervals. The symptoms of these patients suggest a common root for cluster and migraine headaches.     

Scalp and direct cortical recordings of somatosensory evoked potentials in man (circa 1967).

Studied the temporo-spatial aspects of normal somatosensory evoked potentials (SEPs) and cortical SEPs to clarify the multiple neural origins of SEP components. The SEP to median nerve stimulation at the wrist (inducing minimal thumb twitch) was analyzed in 12 males (16–40 yrs). Probable neural origins were proposed, including a subthalamic origin for P15. Cortex SEP recordings in the unanesthetized temporal lobes of 12 epileptics (12–45 yrs) showed an absence of P15 but otherwise showed all major scalp components with, however, increased latencies (cortical cooling). N19 and P25 were regularly present on the postcentral gyrus where direct electrical cortical stimulation produced sensation referred to the contralateral thumb/index finger. Cortex-to-scalp transfer involved amplitude reduction, spatial averaging, and relative suppression of localized waveforms. (French abstract) (80 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

High frequency oscillations in early cortical somatosensory evoked potentials

OBJECTIVE: To evaluate the characteristics of high frequency (HF) components of the early cortical somatosensory evoked potentials (SEPs). METHODS: We recorded 8-channel SEPs from the frontal and left centro-parietal scalp after right median nerve stimulation with a wide band-pass (0.5-2000 Hz) and digitized at 40 kHz sampling rate in 12 healthy subjects. HF components were analyzed after digital band-pass filtering (300-1000 Hz). The power spectrum was obtained by a maximum entropy method. RESULTS: HF oscillations (maximum power at 600-800 Hz) consisting of 5 to 8 peaks were discriminated from the preceding P14 far-field in all cases and their phases were reversed between the frontal and contralateral parietal regions. In addition, in subjects with a high amplitude central P22 potential in original wide-band recordings, a single HF oscillation with a maximum at the central region was present. Furthermore, this component showed no phase reversal over the centro-parietal area. CONCLUSION: We therefore conclude that HF oscillations are superimposed not only on the tangential N20-P20 but on the radial P22 potential, and are generated from both tangential (area 3b) and radial (area 1) current sources.     

Simplified preformed chelate protein radiolabeling with technetium-99m mercaptoacetamidoadipoylglycylglycine (N3S-adipate)

The precentral P22/N30 cortical component of the median nerve somatosensory evoked potentials (SEPs) was recorded in 16 patients (11 women and five men) suffering from cervical dystonia before and after botulinum toxin therapy. Cervical dystonia was diagnosed as idiopathic in all patients: 13 patients suffered from right-sided torticollis, and three suffered from left-sided torticollis. The amplitude of the P22/N30 component and the side-to-side ratio of amplitude values were measured. Normal values were obtained by acquiring measurements in two groups of healthy volunteers (n1 = 20 and n2 = 20). The recordings in the first control group were done with the patient's head in a normal position, whereas, in the second control group, the patient kept the head intentionally rotated 60 degrees to the right. Patients were treated with local injections of botulinum toxin A (BTX-A). The mean duration of treatment was 8.3 months, and the mean total amount of BTX injected was 295 U. The P22/N30 precentral component was repeatedly recorded in patients after head posture had been corrected to the normal plane by BTX-A treatment. The recordings showed that the amplitude of the P22/N30 precentral component recorded contralaterally to the direction of head deviation was significantly higher in patients before treatment than after treatment. Contralateral pretreatment amplitudes were also significantly higher (p < 0.01 and p < 0.05, respectively) than amplitudes in both groups of healthy volunteers. The mean side-to-side ratio of precentral P22/N30 component amplitudes was significantly higher in patients before treatment compared with after treatment and also compared with both control groups. These changes in dystonic patients probably reflect the direction of head rotation, the muscle pattern of torticollis, and the change in force of dystonic contraction after the treatment. The changes presumably could be the result of higher excitability of the precentral cortex contralateral to head rotation in patients with cervical dystonia and its change after successful BTX-A treatment.     

Peripheral nerve repair in the hand with and without motor sensory differentiation

To investigate the value of motor sensory differentiated nerve repair, we examined a group of 9 patients with motor sensory differentiated nerve repair and a group of 13 patients without motor sensory differentiated nerve repair. The clinical and electroneurographic findings were compared. For the clinical examination, Millesi's scoring system was used. The hand function after motor sensory differentiated median nerve repair was 72% +/- 16% compared with 57% +/- 14% without motor sensory differentiation. The hand function after motor sensory differentiated median and ulnar nerve repair was 53% +/- 12% compared with 43% +/- 24% without motor sensory differentiation. After ulnar nerve repair the achieved values for hand function were high even without motor sensory differentiation. Our results indicate that intraoperative motor sensory differentiation of injured nerves is helpful to reestablish particularly the sensory function in median nerve injuries.     

Intra-operative localization of sensorimotor cortex by cortical somatosensory evoked potentials: from analysis of waveforms to dipole source modeling

Intra-operative localization of sensorimotor cortex is of increasing importance as neurosurgical techniques allow safe and accurate removal of lesions around the central sulcus. Although direct cortical recordings of somatosensory evoked potentials (SEPs) are known to be helpful for cortical localization, source localization models can provide more precise estimates than subjective visual analysis. In addition to intra-operative analysis of waveforms and amplitudes of SEPs to median nerve stimulation in 20 neurosurgical patients, we used a spatiotemporal dipole model to determine the location of the equivalent dipoles consistent with the cortical distribution of the SEPs. The early cortical SEPs were modeled by 2 equivalent dipoles located in the postcentral gyrus. The first dipole was primarily tangentially oriented and explained N20 and P20 peaks. The second dipole was primarily radially oriented and explained P25 activity. We found consistent localization of the first dipole in the postcentral gyrus, which was always located within 8 mm of the central sulcus, with an average distance of 3 mm. This finding provides an objective basis for using the SEP phase reversal method for cortical localization. We conclude that dipole source modeling of the cortical SEPs can be considered as an objective way of localizing the cortical hand sensory area.     

Dermatomal and mixed nerve somatosensory evoked potentials in the diagnosis of neurogenic thoracic outlet syndrome

To evaluate the diagnostic utility of dermatomal and mixed nerve somatosensory evoked potentials (SEPs) in patients with thoracic outlet syndrome (TOS) and to compare their value with routine electrodiagnostic methods, we studied a group of 44 patients with neurogenic TOS and 30 healthy controls. In addition to bilateral median and ulnar SEPs, evoked potentials were recorded after stimulation of C6 and C8 dermatomes from the first and fifth digits, respectively. The patients were classified into 3 groups according to the nature of their clinical condition. The abnormality rate for both ulnar and C8 dermatomal SEPs was 100% in a small group of patients with severe neurological signs like atrophy. In groups of patients with lesser degrees of neurogenic damage, abnormality rates for ulnar and C8 dermatomal SEPs on affected limb(s) were 67 and 50%, respectively. Same abnormality rates were 25 and 18% in patients with only subjective symptoms. In patients with objective neurological signs, the major increase in sensitivity was with electromyography (EMG). Abnormalities of routine nerve conduction studies and F-wave latency were observed in patients with severe neurogenic damage. We concluded that the most useful tests in the diagnosis of neurogenic TOS are needle EMG and ulnar SEPs.     

Temporal and binaural properties in dorsal cochlear nucleus and its output tract

The dorsal cochlear nucleus (DCN) is one of three nuclei at the terminal zone of the auditory nerve. Axons of its projection neurons course via the dorsal acoustic stria (DAS) to the inferior colliculus (IC), where their signals are integrated with inputs from various other sources. The DCN presumably conveys sensitivity to spectral features, and it has been hypothesized that it plays a role in sound localization based on pinna cues. To account for its remarkable spectral properties, a DCN circuit scheme was developed in which three inputs converge onto projection neurons: auditory nerve fibers, inhibitory interneurons, and wide-band inhibitors, which possibly consist of Onset-chopper (Oc) cells. We studied temporal and binaural properties in DCN and DAS and examined whether the temporal properties are consistent with the model circuit. Interneurons (type II) and projection (types III and IV) neurons differed from Oc cells by their longer latencies and temporally nonlinear responses to amplitude-modulated tones. They also showed evidence of early inhibition to clicks. All projection neurons examined were inhibited by stimulation of the contralateral ear, particularly by broadband noise, and this inhibition also had short latency. Because Oc cells had short-latency responses and were well driven by broadband stimuli, we propose that they provide short-latency inhibition to DCN for both ipsilateral and contralateral stimuli. These results indicate more complex temporal behavior in DCN than has previously been emphasized, but they are consistent with the recently described nonlinear behavior to spectral manipulations and with the connectivity scheme deduced from such manipulations.     

Glutathione reductase, selenium-dependent glutathione peroxidase, glutathione levels, and lipid peroxidation in freshwater bivalves, Unio tumidus, as biomarkers of aquatic contamination in field studies

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.